plum pudding model experiment name

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Thomson atomic model

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• Academia - J. J. Thomson's plum-pudding atomic model: The making of a scientific myth

Thomson atomic model , earliest theoretical description of the inner structure of atoms , proposed about 1900 by William Thomson (Lord Kelvin) and strongly supported by Sir Joseph John Thomson , who had discovered (1897) the electron , a negatively charged part of every atom . Though several alternative models were advanced in the 1900s by Kelvin and others, Thomson held that atoms are uniform spheres of positively charged matter in which electrons are embedded. Popularly known as the plum pudding model, it had to be abandoned (1911) on both theoretical and experimental grounds in favour of the Rutherford atomic model , in which the electrons describe orbits about a tiny positive nucleus. See also atomic model .

What Is J.J. Thomson’s Plum Pudding Model?

The discovery of the electron, the plum pudding model, the plum pudding model’s failing.

The electrons were the negative plums embedded in a positive pudding. The name stuck, and the model is still commonly referred to as the Plum Pudding Model.

Knowledge can either be derived by acquaintance, such as the color of a tree, or — if the phenomenon is impossible to “become acquainted with” — by description. This would include how an eye detects color or how the colors themselves are created. We call these descriptions models.

However, descriptive knowledge is itself based on other descriptions. For instance, to understand how a color is created, we must first understand the structure of an atom, which itself — being an object a million times thinner than a strand of human hair – can be comprehended only through descriptions. J.J. Thomson’s Plum Pudding Model was one such description of an atom, which was at that time deemed the most fundamental constituent of matter.

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When a voltage is applied between a positive and negative electrode placed in a completely evacuated or vacuumed chamber, the glass or the region of the chamber behind the positive electrode gradually begins to glow. Physicists call this fluorescence. What travels between the electrodes and speckles the glass is invisible. The rays baffled physicists for years, who — given that the rays emanated from the cathode or the negative electrode — simply called them cathode rays.

Earlier, Dalton had proposed that atoms are the fundamental constituent of matter; they are indivisible and indestructible. In the day, physicists believed that the Universe was permeated by a material they called ether, which acted as the medium to propagate light. The rationale was that if waves cannot travel without a medium, how can sunlight reach Earth? Space, they declared, wasn’t empty, but suffused with ether through which light could seamlessly flow. Physicists believed that atoms too were disturbances in this supple ether; they believed that atoms were literally permanent vortices whirling interminably in it.

However, J.J. Thomson was a vehemently practical man, someone well-versed in the principles of science. In view of the poverty of evidence for the existence of ether, Thomson was incredulous. Thus, Thomson decided to look for atoms himself. When Thomson performed the cathode ray experiment, but with a magnet in between, he managed to penetrate reality a bit deeper.

Formerly, it was believed that cathode rays, like light, were distinct and immaterial. However, when Thomson forced them to travel between magnets, he observed that they deflected towards one. He later observed that they were deflected by electric fields as well. Thomson inferred that the particles that constitute cathode rays are charged, and from the deflection, he inferred that the charge was negative.

According to calculations, the particle was found to be tremendously tiny, at least 1000 times smaller than an atom itself. Thomson had discovered the electron. The name, however, was coined by G.J. Stoney. Thomson, in fact, referred to this object as “the negative corpuscle”. As for the ether, it became unnecessary once James Clerk Maxwell successfully proved that light is an electromagnetic wave and therefore doesn’t require a medium to travel.

The discovery was profound. The electron was more fundamental than anything yet discovered. It was the first of the several minuscule objects now called sub-atomic particles to be discovered. However, atoms can’t simply confine a negative charge, because they are, of course, electrically neutral. Thomson immediately realized that there existed a source of positive charge that negated the negative charges and rendered the atom completely neutral.

Thomson, in the prestigious Philosophical Magazine ’s March edition of 1904, proposed a model of the atom according to which the atom was a bounded region of positive charge that was occupied by negative charges. In his own words: “the atoms of the elements consist of a number of negatively charged corpuscles enclosed in a sphere of uniform positive electrification.” The qualifier “uniform” is crucial here. The magnitude of the positivity of the space was equal to the net negative charge generated by the electrons, thus making the atom neutral.

The model, British physicists recognized, was reminiscent of a plum pudding, a dessert adored by the British. The electrons were the negative plums embedded in a positive pudding. The name stuck, and the model is still commonly referred to as the Plum Pudding Model. However, it is also often called the Watermelon Model. I’m sure the connotation is obvious.

However, it’s strange that the name stuck. In Thomson’s model, electrons aren’t stationary like plums or seeds in their pulps. He proposed that they constantly move, or more precisely, rotate very rapidly. The orbits were stable because, as the electrons moved away from the center of the sphere, they were subjected to an even greater positive force, for their orbit now encompassed “more” positive charge. The orbits were further stabilized as the electrons interacted with other electrons. The pushing and pulling negated, thus allowing the electrons to rapidly rotate in circles. However, these very circles proved to be the model’s failing.

In the early 1850s, physicists discovered that elements imparted with energy, for example, by means of heat, emit a distinct pattern of colors. The colors seem discontinuous, but when viewed with what is called a spectroscope, a device that separates colors by their wavelengths, it is seen that the colors are emitted intermittently: the lines of colors are separated by lines of complete darkness. Such a pattern is called an emission spectrum and every element generates a unique pattern. In fact, because every element generates a unique spectrum, scientists use these spectrums to identify known elements or discover new ones.

To determine the accuracy of an atomic model, scientists compare the spectrum that the model predicts for an element with the actual spectrum that the element emits. If every element’s (or at least a substantial number) spectrum is exactly replicated by its model, the checkbox is marked correct. Of course, the checklist is quite extensive, but this is surely a good start. Thomson proposed that the electrons orbiting the center were responsible for the spectrum. However, Thomson’s model couldn’t successfully predict the spectrum of even a single element, not even hydrogen, the element that comprises only a single electron. To achieve the expected results, Thomson tinkered with his model, but it was all in vain. His attempts were unsuccessful.

Then, in 1911, Ernest Rutherford interpreted what is now famously called  The Gold Foil Experiment conducted by Hans Geiger and Ernest Marsden in 1909. Rutherford successfully predicted the existence of an immensely dense concentration of positive charge in the center of atoms. This was called the atom’s nucleus. The atom wasn’t a cloud of positive charge specked with electrons; in fact, it was found to be almost entirely empty. For perspective, if the atom is the stadium, the nucleus would be the baseball.

Despite being proved embarrassingly wrong, Thomson – remember a man well-versed in the principles of science – was rather proud of Rutherford, for he was Thomson’s most prized student. In fact, ironically, it was Thomson’s very own son, George Thomson, who subsequently demonstrated that electrons do not merely behave like “corpuscles”, as his father had described, but also like ripples in a pond. He was the first physicist to experimentally prove the wave nature of electrons.

Each won a Nobel Prize for their revolutionary contributions, for unveiling the strange but true nature of Nature. However, Rutherford’s success seems fortuitous, it was the clenched fist that Thomson decided should not be tapped and asked to be twisted and opened. After performing the cathode ray experiment, Thomson actually made three propositions: 1) each negative charge inhabiting the atom is paired with a positive charge; 2) an atom is a “soup” of uniform positive charge in which negatively charged particles encircle the center like sharks; or 3) the negatively charged particles orbit a central region of positive charge, which has the same magnitude as the net negative charge generated by the “corpuscles”. Thomson had to make a choice. The rest, as they say, is history.

• The Yale-New Haven Teachers Institute - teachersinstitute.yale.edu
• Chapter 6 The Rutherford-Bohr Model of the Atom.
• atomic structure activities for secondary science.

Akash Peshin is an Electronic Engineer from the University of Mumbai, India and a science writer at ScienceABC. Enamored with science ever since discovering a picture book about Saturn at the age of 7, he believes that what fundamentally fuels this passion is his curiosity and appetite for wonder.

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What Is The Plum Pudding Atomic Model?

Ever since it was first proposed by Democritus in the 5th century BCE, the atomic model has gone through several refinements over the past few thousand years. From its humble beginnings as an inert, indivisible solid that interacts mechanically with other atoms, ongoing research and improved methods have led scientists to conclude that atoms are actually composed of even smaller particles that interact with each other electromagnetically.

This was the basis of the atomic theory devised by English physicist J.J. Thompson in the late 19th an early 20th centuries. As part of the revolution that was taking place at the time, Thompson proposed a model of the atom that consisted of more than one fundamental unit. Based on its appearance, which consisted of a “sea of uniform positive charge” with electrons distributed throughout, Thompson’s model came to be nicknamed the “Plum Pudding Model”.

Though defunct by modern standards, the Plum Pudding Model represents an important step in the development of atomic theory. Not only did it incorporate new discoveries, such as the existence of the electron, it also introduced the notion of the atom as a non-inert, divisible mass. Henceforth, scientists would understand that atoms were themselves composed of smaller units of matter and that all atoms interacted with each other through many different forces.

Atomic Theory to the 19th century:

The earliest known examples of atomic theory come from ancient Greece and India, where philosophers such as Democritus postulated that all matter was composed of tiny, indivisible and indestructible units. The term “atom” was coined in ancient Greece and gave rise to the school of thought known as “atomism”. However, this theory was more of a philosophical concept than a scientific one.

It was not until the 19th century that the theory of atoms became articulated as a scientific matter, with the first evidence-based experiments being conducted. For example, in the early 1800s, English scientist John Dalton used the concept of the atom to explain why chemical elements reacted in certain observable and predictable ways.

Dalton began with the question of why elements reacted in ratios of small whole numbers and concluded that these reactions occurred in whole-number multiples of discrete units – i.e. atoms. Through a series of experiments involving gases, Dalton went on to develop what is known as Dalton’s Atomic Theory . This theory expanded on the laws of conversation of mass and definite proportions – formulated by the end of the 18th century – and remains one of the cornerstones of modern physics and chemistry.

The theory comes down to five premises: elements, in their purest state, consist of particles called atoms; atoms of a specific element are all the same, down to the very last atom; atoms of different elements can be told apart by their atomic weights; atoms of elements unite to form chemical compounds; atoms can neither be created or destroyed in chemical reaction, only the grouping ever changes.

By the late 19th century, scientists also began to theorize that the atom was made up of more than one fundamental unit. However, most scientists ventured that this unit would be the size of the smallest known atom – hydrogen. By the end of the 19th century, the situation would change drastically.

Thompson’s Experiments:

Sir Joseph John Thomson (aka. J.J. Thompson) was an English physicist and the Cavendish Professor of Physics at the University of Cambridge from 1884 onwards. During the 1880s and 1890s, his work largely revolved around developing mathematical models for chemical processes, the transformation of energy in mathematical and theoretical terms, and electromagnetism.

However, by the late 1890s, he began conducting experiments using a cathode ray tube known as the Crookes’ Tube . This consists of a sealed glass container with two electrodes that are separated by a vacuum. When voltage is applied across the electrodes, cathode rays are generated (which take the form of a glowing patch of gas that stretches to the far end of the tube).

Through experimentation, Thomson observed that these rays could be deflected by electric and magnetic fields. He concluded that rather than being composed of light, they were made up of negatively charged particles he called “corpuscles”. Upon measuring the mass-to-charge ration of these particles, he discovered that they were 1ooo times smaller and 1800 times lighter than hydrogen.

This effectively disproved the notion that the hydrogen atom was the smallest unit of matter, and Thompson went further to suggest that atoms were divisible. To explain the overall charge of the atom, which consisted of both positive and negative charges, Thompson proposed a model whereby the negatively charged corpuscles were distributed in a uniform sea of positive charge.

These corpuscles would later be named “electrons”, based on the theoretical particle predicted by Anglo-Irish physicist George Johnstone Stoney in 1874. And from this, the Plum Pudding Model was born, so named because it closely resembled the English desert that consists of plum cake and raisins. The concept was introduced to the world in the March 1904 edition of the UK’s Philosophical Magazine , to wide acclaim.

Problems With the Plum Pudding Model:

Unfortunately, subsequent experiments revealed a number of scientific problems with the model. For starters, there was the problem of demonstrating that the atom possessed a uniform positive background charge, which came to be known as the “Thomson Problem”. Five years later, the model would be disproved by Hans Geiger and Ernest Marsden, who conducted a series of experiments using alpha particles and gold foil.

In what would come to be known as the “ gold foil experiment “, they measured the scattering pattern of the alpha particles with a fluorescent screen. If Thomson’s model were correct, the alpha particles would pass through the atomic structure of the foil unimpeded. However, they noted instead that while most shot straight through, some of them were scattered in various directions, with some going back in the direction of the source.

Geiger and Marsden concluded that the particles had encountered an electrostatic force far greater than that allowed for by Thomson’s model. Since alpha particles are just helium nuclei (which are positively charged) this implied that the positive charge in the atom was not widely dispersed, but concentrated in a tiny volume. In addition, the fact that those particles that were not deflected passed through unimpeded meant that these positive spaces were separated by vast gulfs of empty space.

By 1911, physicist Ernest Rutherford interpreted the Geiger-Marsden experiments and rejected Thomson’s model of the atom. Instead, he proposed a model where the atom consisted of mostly empty space, with all its positive charge concentrated in its center in a very tiny volume, that was surrounded by a cloud of electrons. This came to be known as the Rutherford Model of the atom.

Subsequent experiments by Antonius Van den Broek and Neils Bohr refined the model further. While Van den Broek suggested that the atomic number of an element is very similar to its nuclear charge, the latter proposed a Solar-System-like model of the atom, where a nucleus contains the atomic number of positive charge and is surrounded by an equal number of electrons in orbital shells (aka. the Bohr Model ).

Though it would come to be discredited in just five years time, Thomson’s “Plum Pudding Model” would prove to be a crucial step in the development of the Standard Model of particle physics. His work in determining that atom’s were divisible, as well as the existence of electromagnetic forces within the atom, would also prove to be major influence on the field of quantum physics.

We have written many interesting articles on the subject of atomic theory here at Universe Today. For instance, here is How Many Atoms Are There In The Universe? , John Dalton’s Atomic Model , What Are The Parts Of The Atom? , Bohr’s Atomic Model ,

For more information, be sure to check out Physic’s Worlds pages on 100 years of the electron: from discovery to application and Proton and neutron masses calculated from first principles

Astronomy Cast also has some episodes on the subject: Episode 138: Quantum Mechanics , Episode 139: Energy Levels and Spectra, Episode 378: Rutherford and Atoms and Episode 392: The Standard Model – Intro .

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The History of the Atomic Model: Thomson and the Plum Pudding

J.J Thomson contributed massively to the model of the atom and the modern day theory. His work involved the use of cathode ray tubes and identifying a particle lighter than the atom itself, the electron.

Refresher : The atomic model originated in the 5th century BC when Greek philosophers hypothesized that all matter was composed of indivisible particles. The modern atomic model started to take shape with the work of Lavoisier and Dalton who formulated the concept of elements as unique iterations of atoms which can be combined in multiple ways to create a variety of substances. This work was later expanded upon by chemists throughout the 19th century and beyond to create the modern model of the atom, which arose after the rise and fall of many partial theories. 

1. Who came up with the plum pudding model?

J. J. Thomson created the plum pudding model. 

2. Is the plum pudding model correct?

While the plum pudding model was the first to suggest that atoms are made up of charged particles, the plum pudding model is not entirely correct. Instead of a sea of positive charges surrounding negative charged particles, atoms are actually organized with positive and neutral particles at their core (the nucleus) surrounded by orbitals of electrons. 

3. What did the plum pudding model suggest about atoms?

The plum pudding model was the first model to suggest that atoms were not the smallest unit of matter, and that they may be made up of both positive and negatively charged subatomic particles. 

How the Plum Pudding Model Came to Be

For a long time, atoms were thought to be the smallest unit of matter. This theory was established by Dalton and the atomists who stated that matter was made up of small indivisible particles known as elements which varied in their nature. The work of Avogadro on the volumes of gases and Robert Brown on Brownian motion further supported this hypothesis. However, in 1897, the English physicist J. J. Thomson discovered that there was a particle smaller than an atom -  the electron - through his work with cathode ray tubes. 

To create a cathode ray tube, Thomson applied a voltage to one side of a sealed glass container with two electrodes. Most of the air was removed from the tube, but when the voltage is applied, the remaining particles flowed from the cathode to the anode. Chemists called this particle flow “cathode rays,” and they were able to detect them by placing a material called phosphors in the tube. Thomson decided to set up additional electric plates around the cathode ray to determine whether the cathode beams were charged. When the cathode ray was attracted toward the positively charged plate, he realized that the rays must be made up of negatively charged particles. 

Thomson concluded that these rays were not light but instead made of negatively charged particles. He measured the mass of the particles and discovered they were 1800 times smaller than that of the element hydrogen. This led him to conclude that these particles were a smaller piece of matter than the atom itself. He further concluded that these small particles were building blocks of larger particles. He theorised that to balance out this negative charge present in these small particles, they must be surrounded by a positively charged matter that made up the matrix of the atom. This led him to hypothesise the plum pudding model of the atom, where a sea of negative particles (electrons, as we now call them) were surrounded by a cloud of positive charge to balance them out. The model was named after a common english dessert which has raisins dispersed throughout a matrix of cake.

About the Author

Nathan has a degree in BSc Biomedical Chemistry at Warwick University and a degree in PGCE Science at Wolverhampton University, UK. Nathan's subject matter ranges from general chemistry and organic chemistry. Nathan also created the curriculum on Breaking Atom in the course page.

Terms in section

Corpuscularism was a theory proposed by Descartes that all matter was composed of tiny particles.

Rene Descartes was a famous mathematician and philosopher of the 16th century who hypothesised the theory of corpuscularism about the atom

Luster is a term for a reflective surface that reflects light giving a shiny appearance.

Semi conductors is a term to describe metalloids that are able to conduct a current when electrical energy is applied due to the movement of electrons but the conductivity measurements are not as high as metals due to fewer electrons to carry a charge or a less ordered structure.

An ionic compound is a bond that forms between metals and non metals to form a large ionic lattice

Nuclear fusion is a process which occurs in. the sun. Hydrogen atoms under a lot of heat and pressure are forced together to make a larger atom of helium

Heisenberg’s uncertainty principle is used to describe the relationship between the momentum and position of an electron. Where by if the exact position of the electron is known the momentum will be uncertain.

Werner Heisenberg was a German physicist who was a pioneer in the field of quantum mechanics. He devised the principle of uncertainty relating to the momentum and position of an electron.

Lobes refers to the shape of electron waves and the area of highest probability of where that electron as a particle would be found.

The Pauli Exclusion refers to the theory that each electron can only have a unique set of the 4 quantum numbers and no two electrons can have the same quantum numbers

Quantum numbers is a term used to describe the assigning of numbers to electrons as a mathematical function to describe their momentum and energy.

The Bohr model refers to the treatment of electrons as particles that orbit the nucleus.

The term quantum mechanics refers to energy levels and the theoretical area of physics and chemistry where mathematics is used to explain the behaviour of subatomic particles.

A trough is the lowest point on a transverse wave.

A peak is the highest point on a transverse wave.

Vibrational modes is a term used to describe the constant motion in a molecule. Usually these are vibrations, rotations and translations.

Erwin Schrodinger was an Austrian physicist who used mathematical models to enhance the Bohr model of the electron and created an equation to predicted the likelihood of finding an electron in a given position.

The alkali metals, found in group 1 of the periodic table (formally known as group IA), are so reactive that they are generally found in nature combined with other elements. The alkali metals are shiny, soft, highly reactive metals at standard temperature and pressure.

Alkaline earth metals is the second most reactive group of elements in the periodic table. They are found in group 2 of the periodic table (formally known as group IIA).

Unknown elements (or transactinides) are the heaviest elements of the periodic table. These are meitnerium (Mt, atomic number 109), darmstadtium (Ds, atomic number 110), roentgenium (Rg, atomic number 111), nihonium (Nh, atomic number 113), moscovium (Mc, atomic number 115), livermorium (Lv, atomic number 116) and tennessine (Ts, atomic number 117).

The post-transition metals are the ones found between the transition metals (to the left) and the metalloids (to the right). They include aluminium (Al), gallium (Ga), indium (In), thallium (Tl), tin (Sn), lead (Pb) and bismuth (Bi).

Oganesson (Og) is a radioactive element that has the atomic number 118 in the periodic table, its appearance is not fully known due to the minuscule amounts produced of it. It is in Group 18. It has the symbol Og.

Tennessine (Ts) is a radioactive element that has the atomic number 117 in the periodic table, its appearance is not fully known due to the minuscule amounts produced of it. It is in Group 17. It has the symbol Ts.

Livermorium (Lv) is a radioactive element that has the atomic number 116 in the periodic table, its appearance is not fully known due to the minuscule amounts produced of it. It is in Group 16. It has the symbol Lv.

Moscovium (Mc) is a radioactive metal that has the atomic number 115 in the periodic table, its appearance is not fully known due to the minuscule amounts produced of it. It is in Group 15. It has the symbol Mc.

Flerovium (Fl) is a radioactive metal that has the atomic number 114 in the periodic table, its appearance is not fully known due to the minuscule amounts produced of it. It is in Group 14. It has the symbol Fl.

Nihonium (Nh) is a radioactive metal that has the atomic number 112 in the periodic table, its appearance is not fully known due to the minuscule amounts produced of it. It is in Group 13. It has the symbol Nh.

Copernicium (Cr) is a radioactive metal that has the atomic number 112 in the periodic table, its appearance is not fully known due to the minuscule amounts produced of it. It is a Transition metal in Group 11. It has the symbol Rg.

Roentgenium (Rg) is a radioactive metal that has the atomic number 111 in the periodic table, its appearance is not fully known due to the minuscule amounts produced of it. It is a Transition metal in Group 11. It has the symbol Rg.

Darmstadtium (Ds) is a radioactive metal that has the atomic number 110 in the periodic table, its appearance is not fully known due to the minuscule amounts produced of it. It is a Transition metal in Group 10. It has the symbol Ds

Meitnerium (Mt) is a radioactive metal that has the atomic number 109 in the periodic table, its appearance is not fully known due to the minuscule amounts produced of it. It is a Transition metal in Group 9. It has the symbol Mt.

Hassium (Hs) is a radioactive metal that has the atomic number 108 in the periodic table, its appearance is not fully known due to the minuscule amounts produced of it. It is a Transition metal in Group 8. It has the symbol Hs.

Bohrium (Bh) is a radioactive metal that has the atomic number 107 in the periodic table, its appearance is not fully known due to the minuscule amounts produced of it. It is a Transition metal in Group 7. It has the symbol Bh.

Seaborgium (Sg) is a radioactive metal that has the atomic number 106 in the periodic table, its appearance is not fully known due to the minuscule amounts produced of it. It is a Transition metal in Group 6. It has the symbol Sg.

Dubnium (Db) is a radioactive metal that has the atomic number 105 in the periodic table, its appearance is not fully known due to the minuscule amounts produced of it. It is a Transition metal in Group 5. It has the symbol Db.

Rutherfordium (Rf) is a radioactive metal that has the atomic number 104 in the periodic table, its appearance is not fully known due to the minuscule amounts produced of it. It is a Transition metal in Group 4. It has the symbol Rf.

Lawrencium (Lr) is a silvery-white colored radioactive metal that has the atomic number 103 in the periodic table. It is an Actinoid Metal with the symbol Lr.

Nobelium (No) is a radioactive metal that has the atomic number 102 in the periodic table, its appearance is not fully known due to the minuscule amounts produced of it. It is an Actinoid Metal with the symbol No.

Mendelevium (Md) is a radioactive metal that has the atomic number 101 in the periodic table, its appearance is not fully known due to the minuscule amounts produced of it. It is an Actinoid Metal with the symbol Md.

Fermium (Fm) is a silvery-white colored radioactive metal that has the atomic number 100 in the periodic table. It is an Actinoid Metal with the symbol Fm.

Einsteinium (Es) is a silvery-white colored radioactive metal that has the atomic number 99 in the periodic table. It is an Actinoid Metal with the symbol Es.

Californium (Cf) is a silvery-white colored radioactive metal that has the atomic number 98 in the periodic table. It is an Actinoid Metal with the symbol Cf.

Berkelium (Bk) is a silvery colored radioactive metal that has the atomic number 97 in the periodic table. It is an Actinoid Metal with the symbol Bk.

Curium (Cm) is a silvery-white colored radioactive metal that has the atomic number 96 in the periodic table. It is an Actinoid Metal with the symbol Cm.

Americium (Am) is a silvery colored radioactive metal that has the atomic number 95 in the periodic table. It is an Actinoid Metal with the symbol Am.

Plutonium (Pu) is a silvery colored radioactive metal that has the atomic number 94 in the periodic table. It is an Actinoid Metal with the symbol Pu.

Neptunium (Np) is a silvery colored radioactive metal that has the atomic number 93 in the periodic table. It is an Actinoid Metal with the symbol Np.

Protactinium (Pa) is a shiny silver colored radioactive metal that has the atomic number 91 in the periodic table. It is an Actinoid Metal with the symbol Pa.

Thorium (Th) is a silvery-white colored radioactive metal that has the atomic number 90 in the periodic table. It is an Actinoid Metal with the symbol Th.

Actinium (Ac) is a silvery colored radioactive metal that has the atomic number 89 in the periodic table. It is an Actinoid Metal with the symbol Ac.

Radium (Ra) is a silvery-white colored metal that has the atomic number 88 in the periodic table. It is an Alkaline earth Metal with the symbol Ra and is located in Group 2 of the periodic table.

Francium (Fr) is thought to be a gray colored metal that has the atomic number 87 in the periodic table. It is an Alkali Metal with the symbol Fr and is located in Group 1 of the periodic table.

Radon (Rn) is a colourless, odourless, radioactive gas non-metal that has the atomic number 86 in the periodic table in Group 18. It has the symbol Rn.

Astatine (At) is a radioactive non-metal that has the atomic number 85 in the periodic table in Group 17. It has the symbol At.

Polonium (Po) is a silvery-gray metal that has the atomic number 84 in the periodic table in Group 16. It has the symbol Po.

Bismuth (Bi) is a hard steel-gray metal that has the atomic number 83 in the periodic table in Group 15. It has the symbol Bi.

Lead (Pb) is a soft gray metal that has the atomic number 82 in the periodic table in Group 14. It has the symbol Pb.

Thallium (Tl) is a soft gray metal that has the atomic number 81 in the periodic table in Group 13. It has the symbol Tl.

Mercury (Hg) is a liquid silver coloured metal that has the atomic number 80 in the periodic table. It is a Transition metal in Group 12. It has the symbol Hg.

Gold (Au) is a soft gold coloured metal that has the atomic number 79 in the periodic table. It is a Transition metal in Group 11. It has the symbol Au.

Platinum (Pt) is a heavy white metal that has the atomic number 78 in the periodic table. It is a Transition metal in Group 10. It has the symbol Pt.

Iridium (Ir) is a heavy white metal that has the atomic number 77 in the periodic table. It is a Transition metal in Group 9. It has the symbol Ir.

Osmium (Os) is a hard fine black powder or blue-white metal that has the atomic number 76 in the periodic table. It is a Transition metal in Group 8. It has the symbol Os.

Rhenium (Re) is a silvery-white coloured metal that has the atomic number 75 in the periodic table. It is a Transition metal in Group 7. It has the symbol Re.

Tungsten (W) is a steel-gray coloured metal that has the atomic number 74 in the periodic table. It is a Transition metal in Group 6. It has the symbol W.

Tantalum (Ta) is a gray coloured metal that has the atomic number 73 in the periodic table. It is a Transition metal in Group 5. It has the symbol Ta.

Hafnium (Hf) is a silvery coloured metal that has the atomic number 72 in the periodic table. It is a Transition metal in Group 4. It has the symbol Hf.

Lutetium (Lu) is a silvery-white coloured metal that has the atomic number 71 in the periodic table. It is a Lanthanide metal. It has the symbol Lu.

Ytterbium (Yb) is a silvery coloured metal that has the atomic number 70 in the periodic table. It is a Lanthanide metal. It has the symbol Yb.

Thulium (Tm) is a silvery coloured metal that has the atomic number 69 in the periodic table. It is a Lanthanide metal. It has the symbol Tm.

Erbium (Er) is a silvery coloured metal that has the atomic number 68 in the periodic table. It is a Lanthanide metal. It has the symbol Er.

Holmium (Ho) is a silvery coloured metal that has the atomic number 67 in the periodic table. It is a Lanthanide metal. It has the symbol Ho.

Dysprosium (Dy) is a silvery coloured metal that has the atomic number 66 in the periodic table. It is a Lanthanide metal. It has the symbol Dy.

Terbium (Tb) is a silvery-gray coloured metal that has the atomic number 65 in the periodic table. It is a Lanthanide metal. It has the symbol Tb.

Gadolinium (Gd) is a silvery-white coloured metal that has the atomic number 64 in the periodic table. It is a Lanthanide metal. It has the symbol Gd.

Europium (Eu) is a silvery-white coloured metal that has the atomic number 63 in the periodic table. It is a Lanthanide metal. It has the symbol Eu.

Samarium (Sm) is a silvery coloured metal that has the atomic number 62 in the periodic table. It is a Lanthanide metal. It has the symbol Sm.

Promethium (Pm) is a rare metal that has the atomic number 61 in the periodic table. It is a Lanthanide metal. It has the symbol Pm.

Neodymium (Nd) is a silvery white coloured metal that has the atomic number 60 in the periodic table. It is a Lanthanide metal. It has the symbol Nd.

Praseodymium (Pr) is a silvery white coloured metal that has the atomic number 59 in the periodic table. It is a Lanthanide metal. It has the symbol Pr.

Cerium (Ce) is a iron-gray coloured metal that has the atomic number 58 in the periodic table. It is a Lanthanide metal. It has the symbol Ce.

Lanthanum (La) is a soft silvery white coloured metal that has the atomic number 57 in the periodic table. It is a Lanthanide metal. It has the symbol La.

Barium (Ba) is a soft silvery white coloured metal that has the atomic number 56 in the periodic table. It is an Alkaline earth metal and is located in Group 2 of the periodic table. it has the symbol Ba.

Caesium (Cs) is a soft gray coloured metal that has the atomic number 55 in the periodic table. It is an Alkali Metal and is located in Group 1 of the periodic table. it has the symbol Cs.

Xenon (Xe) exists as a colourless, odourless gas and is chemically inert. It has the atomic number 54 in the periodic table and belongs in Group 18, the Noble Gases. It is a non metal with the symbol Xe.

Iodine (I) is a purple grey solid non metal. It has the atomic number 53 in the periodic table. It is located in Group 17, the Halogens. It has the symbol I.

Tellurium (Te) is a silver-white semi metal that has the atomic number 52 in the periodic table. It is located in Group 16 of the periodic table. It has the symbol Te.

Antimony (Sb) is a hard brittle silver-white semi metal that has the atomic number 51 in the periodic table. It is located in Group 15 of the periodic table. It has the symbol Sb.

Tin (Sn) is a silver-white metal that has the atomic number 50 in the periodic table. It is located in Group 14 of the periodic table. It has the symbol Sn.

Indium (In) is a silver-white metal that has the atomic number 49 in the periodic table. It is located in Group 13 of the periodic table. It has the symbol In.

Cadmium (Cd) is a blue-white metal that has the atomic number 48 in the periodic table. It is a Transition metal and located in Group 12 of the periodic table. It has the symbol Cd.

Silver (Ag) is a silver metal that has the atomic number 47 in the periodic table. It is a Transition metal and located in Group 11 of the periodic table. It has the symbol Ag.

Palladium (Pd) is a silver-white metal that has the atomic number 46 in the periodic table. It is a Transition metal and located in Group 10 of the periodic table. It has the symbol Pd.

Rhodium (Rh) is a brittle silver-white metal that has the atomic number 45 in the periodic table. It is a Transition metal and located in Group 9 of the periodic table. It has the symbol Rh.

Ruthenium (Ru) is a brittle silver-gray metal that has the atomic number 44 in the periodic table. It is a Transition metal and located in Group 8 of the periodic table. It has the symbol Ru.

Technetium (Tc) is a silvery-gray metal that has the atomic number 43 in the periodic table. It is a Transition metal and located in Group 7 of the periodic table. It has the symbol Tc.

Molybdenum (Mo) is a silvery-white metal that has the atomic number 42 in the periodic table. It is a Transition metal and located in Group 6 of the periodic table. It has the symbol Mb.

Niobium (Nb) is a shiny white metal that has the atomic number 41 in the periodic table. It is a Transition metal and located in Group 5 of the periodic table. It has the symbol Nb.

Zirconium (Zr) is a gray white metal that has the atomic number 40 in the periodic table. It is a Transition metal and located in Group 4 of the periodic table. It has the symbol Zr.

Yttrium (Y) is a silvery metal that has the atomic number 39 in the periodic table. It is a Transition metal and located in Group 3 of the periodic table. It has the symbol Y.

Robert Brown was a Scottish scientist who observed small particles in solution moving randomly. His theory came to be known as Brownian motion

Brownian motion is a term used to describe the movement of small particles in random directions and was used as evidence to show that atoms existed due to their ability to collide with each other.

Amadeo Avogado was an Italian scientist who discovered the relationship between gases and the number of particles in a volume of a gas. He also discovered the mole as a quantity to describe the number of particles in a given quantity that could be exchanged between a solid, liquid and gas.

J Thomson was an English physicist who is credited with discovering the electron and theorising the first model of the atom to use sub atomic particles. He proposed the plum pudding model.

The electron is the smallest sub atomic particle that make up the atom. Has a negative charge and is located in shells that orbit the nucleus

The Cathode ray tube is a device which uses electrons being fired through a vacuum onto a screen. J.J Thomson used this to predict the mass of an electron and its existence as a particle smaller than the atom.

An electrode is a conductive part of an electrical circuit that is usually in contact with a non-metallic substance.

A vacuum exists when all particles have been removed from a container creating a space with no particles in.

The plum pudding model was suggested as the first atomic model by J.J Thomson where he suggested that the atom was a sea of positive charge that surrounded small negative electrons

The History of the Atomic Model: Rutherford and Bohr

The History of the Atomic Model: Lavoiser and Dalton

Periodic tables.

• Structure of Atom
• Thomsons Model

Thomson's Atomic model

Thomson model introduction.

Thomson atomic model was proposed by William Thomson in the year 1900. This model explained the description of an inner structure of the atom theoretically. It was strongly supported by Sir Joseph Thomson, who had discovered the electron earlier.

During cathode ray tube experiment, a negatively charged particle was discovered by J.J. Thomson. This experiment took place in the year 1897. Cathode ray tube is a vacuum tube. The negative particle was called an electron.

Table of Contents

• Limitations

Recommended Videos

• Frequently Asked Questions – FAQs

Thomson assumed that an electron is two thousand times lighter than a proton and believed that an atom is made up of thousands of electrons. In this atomic structure model, he considered atoms surrounded by a cloud having positive as well as negative charges. The demonstration of the ionization of air by X-ray was also done by him together with Rutherford. They were the first to demonstrate it. Thomson’s model of an atom is similar to a plum pudding.

Postulates of Thomson’s atomic model

Postulate 1: An atom consists of a positively charged sphere with electrons embedded in it

Postulate 2: An atom as a whole is electrically neutral because the negative and positive charges are equal in magnitude

Thomson atomic model is compared to watermelon. Where he considered:

• Watermelon seeds as negatively charged particles
• The red part of the watermelon as positively charged

Limitations of Thomson’s atomic model

• It failed to explain the stability of an atom because his model of atom failed to explain how a positive charge holds the negatively charged electrons in an atom. Therefore, This theory also failed to account for the position of the nucleus in an atom
• Thomson’s model failed to explain the scattering of alpha particles by thin metal foils
• No experimental evidence in its support

Although Thomson’s model was not an accurate model to account for the atomic structure, it proved to be the base for the development of other atomic models. Find the atomic structure pdf here. The study of the atom and its structure has paved the way for numerous inventions that have played a significant role in the development of humankind. To follow more download BYJU’S – the learning app.

Frequently Asked Questions – FAQs

Why was thomson’s atomic model discarded.

It was discarded because he was unable to precisely account for the stability of the atom. He proposed that electrons are distributed in the atom in the same way that seeds are distributed in a watermelon or dry fruits are distributed in a Christmas pudding.

What is the important feature of Thomson atomic model?

The following are the characteristics of the Thomson model of an atom: (i) An atom is made up of a positively charged sphere in which electrons are embedded. (ii) The magnitudes of the negative and positive charges are the same. As a result, the atom is electrically neutral as a whole.

Which model best explains the atom’s neutrality?

According to Thomson’s atomic model, an atom is made up of a positively charged sphere into which negatively charged electrons are implanted. Because electrons and protons have the same magnitude, an atom as a whole is electrically neutral.

To which fruit has Thomson’s model been compared to?

The model was compared to a watermelon because the red edible part of a watermelon was compared to the sphere with a positive charge, and the black seeds filling the watermelon resembled the electrons inside the sphere.

What was missing from Thomson’s atomic model?

His model lacked a nucleus, protons, and neutrons.

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Thompson Atomic Model

Limitations, significance.

Following his discovery of the electron in 1897, British Physicist J.J. Thomson proposed a model of the atom in 1904 after doing a series of cathode tube experiments. According to his hypothesis, an atom consists of positive and negative charges present in equal amounts so that it is electrically neutral. He proposed that the atom was a sphere with charges embedded within it. This model became known as Thomson Atomic Model [1-4] .

Later models established that the atom consists of a nucleus having positively-charged protons and neutral neutrons, with negatively-charged electrons surrounding the nucleus. Nevertheless, Thomson’s model is significant because it introduced the idea that an atom consists of charged particles.

Thomson’s model became known as the “plum pudding model” or “chocolate chip cookie model”. It envisioned electrons being enclosed within a uniform sphere of positive charge, similar to blueberries inserted into a muffin. The positive substance was likened to jelly or a thick soup, and the electrons were believed to possess some degree of mobility. When the electrons approach the outer part of the atom, the positive charge at the center exceeds the nearby negative charges, causing the electron to be attracted back toward the central region of the atom.

Thomson’s atomic model had numerous limitations that were ultimately overcome by further experiments and research by various scientists. Some of the limitations of Thomson’s Atomic Model are: [1-4]

• It failed to consider the existence of positively charged particles within the atom, a discovery attributed later to Ernest Rutherford, who identified them as protons. Instead, the model presumed a uniform positive charge distribution throughout the atom.
• It did not explain how the positive charge contained the negatively charged electrons. In other words, it could not justify the atom’s stability.
• It could not account for the outcomes of Rutherford’s gold foil experiment. Rutherford’s experiment revealed that most of an atom’s mass and positive charge is concentrated in a minute, dense nucleus at the center of the atom. Thomson’s model did not state the presence of a nucleus in the atom.
• It could not explain atomic spectra, which are the emission and absorption of specific wavelengths of light by atoms.
• It could not explain the presence of isotopes.

Though the Thomson Atomic Model may have proven inaccurate, it was significant in advancing atomic theory and modern physics. Based on scientific evidence and logical reasoning, it transformed subsequent research and experimentation [1-4] .

Moreover, the model’s significance extended beyond its limitations. It challenged the idea that atoms are indivisible and unchangeable entities, a belief held by ancient philosophers. Instead, it revealed the existence of internal structures and subatomic particles within atoms, steering new areas of exploration into the nature of matter and energy.

Furthermore, the model’s impact was not confined to physics alone. It acted as a source of inspiration for Niels Bohr, who developed his quantum model of the atom, successfully integrating classical and quantum mechanics.

Despite its eventual replacement by more accurate models, Thomson Atomic Model retains historical and scientific significance. Its influence echoed throughout other scientific and cultural spheres, engraving its place in the annals of atomic theory’s history.

Ans. Rutherford disproved the Plum Pudding Model of the atom by presenting his gold foil experiment.

Ans. Thomson’s experiments with cathode ray tubes helped him to discover the electron, which Dalton did not know.

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The Plum Pudding Model: An Early Attempt to Explain the Atom

What is the Plum Pudding Model?

How did thomson come up with the plum pudding model, what were the limitations of the plum pudding model, what is the significance of the plum pudding model.

About Electrical4U

Thomson’s Atomic Model: Plum Pudding Model of Atom

• Updated by Scienly
• On September 9, 2024

In this chapter, you will understand Thomson’s atomic model , also known as plum pudding model of atom and its drawbacks or limitations. After the discovery of sub-atomic particles, such as electron and proton, the scientists were faced several major challenges:

• to understand the stability of atom.
• to compare the behaviour of elements based on their physical and chemical properties.
• to explain the formation of different kinds of molecules by the combination of different atoms.
• to understand the origin and nature of the characteristics of electromagnetic radiation absorbed or emitted by atoms.

Scientists proposed various atomic models to explain the arrangement and distribution of charged particles (electrons and protons) within an atom. While some of these models failed to explain the stability of atoms, two notable models that made significant contributions were:

• J.J. Thomson’s Atomic Model (1904)
• Ernest Rutherford’s Model (1911)

J. J. Thomson’s Atomic Model

After the discovery of electrons and protons within an atom, the next question was to know how these particles are arranged in an atom. In 1898, J. J. Thomson was proposed the first scientific model to explain the internal structure of an atom. This atomic model is also popularly known as plum pudding model of the atom. He proposed his model of an atom before the discovery of the neutron.

J. J. Thomson proposed that an atom consists of a uniform sphere, with a radius of approximately 10 -10 m or 10 -8 cm in which the positive charge is uniformly distributed over the entire sphere. The negatively charged particles (electrons) are embedded within this sphere in such a way that they create the most stable electrostatic arrangement.

At equilibrium, the total positive charge inside the atom is equal to the total negative charge possessed by the electrons. As a result, the net charge in the system is zero, making every atom is electrically neutral.

Positive charge = negative charge (at equilibrium)

An important feature of Thomson’s atomic model is that the mass of the atom is considered to be uniformly distributed throughout the atom. This model of atom has given many different names, such as plum pudding model, or raisin pudding model or watermelon model. It successfully described the phenomenon of thermionic emission, photoelectric emission, and ionization.

Why Is Thomson’s Atomic Model Called Plum Pudding Model?

J. J. Thomson’s model is called the “plum pudding model” because he compared the atom to a British Christmas cake known as plum pudding. In this model, the atom is visualized as a soft, round pudding that represents the positive charge, and electrons like small plums scattered throughout over the pudding.

According to the plum pudding model, the positive charge and the electrons are mixed together inside the atom, similar to how plums are mixed into a pudding. Hence, the plum pudding model of the atom describes an atom as a sphere of positive charge with electrons embedded within it, much like plums into pudding.

Drawbacks or Limitations of Thomson’s Model of Atom

Although this atomic model was able to explain the overall neutrality of the atom, but over the development of new concepts, this model was discarded because of the following reasons:

• This model failed to explain the origin of the spectral lines in the form of series observed in atomic spectra. For example, hydrogen atom. Niels Bohr’s model and quantum mechanics explained it later.
• It failed to explain the scattering of alpha particles through the large angles in the Ernest Rutherford’s gold foil experiment in 1909.

Thomson’s atomic model was an earlier step in the development of atomic theory because it introduced the concept of the electron. He was awarded by Nobel Prize for physics in 1906, for his theoretical and experimental researches on the conduction of electricity by gases.

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Home → Features → Natural Sciences → Physics → Matter and Energy

The Plum Pudding Model: how a flawed idea was instrumental in our understanding of the atom

The tale of how an old British cake influenced leading physicists.

The Thomson model, most commonly called the “Plum Pudding” model, was an early attempt to explain what the structure of the atom was like. While the attempt did not really describe the atomic structure accurately, it got a few things right, which set the stage for further developments in atomic research. The plum pudding model was an important departure from earlier atomic models that deserves its place in history.

The JJ Thompson model

In 1904, British physicist J. J. Thomson proposed his idea of what the atom looked like. It was an unusual, but plausible construction that was well-received in the scientific community. Whereas early atom models said that atoms were indivisible and had no internal structure, Thomson argued that the atom must have a structure consisting of some things that are positively charged and other things that are negatively charged.

A few years earlier, Thomson had discovered the electron — a small, subatomic, negatively charged particle. Thomson was trying to reconcile two of the known properties of the atom: that electrons have a negative charge, and the overall atom is neutral.

If electrons are negative and the atom is neutral, then something must be positive. So Thomson came up with a distribution that made sense at the time — in quaint British fashion, he called it the Plum Pudding Model.

The Plum Pudding Model has electrons surrounded by a volume of positive charge in which negative-charge electrons are embedded. It was relatively short-lived: in 1911, Ernest Rutherford published results showing a small nucleus of positive charge, instead of a large mass around the electrons.

So just to clarify: we now know that the plum pudding model is inaccurate. But it’s useful to learn about it, see how it was developed, and how scientists realized that something else was happening.

An atomic model

The idea that matter is made of atoms goes back a long time, but for two thousand years, it fell out of the spotlight.

The Greek philosopher Democritus, born around the year 460 BC, promoted what was regarded by many as a crazy idea: everything we see around us is made of small, individual constituents. He called these constituents “atomos”, or atoms, as we’d call them in English.

Some of the ideas Democritus had turned out to be remarkably correct, showing just how good the intuitive understanding of the Greek philosopher was. He believed that atoms are invisible to the human eye, but they do have a geometry and an internal structure. They are always in motion, are separated by void, and individual atoms are indestructible — we now know atoms are not indestructible, but much of what Democritus said is on point.

Although some philosophers still considered it, the atomic idea of Democritus was largely abandoned for centuries, particularly as it was disregarded by his followers Plato and Aristotle. Plato, who believed that all matter is made of the four elements (earth, fire, wind, and water), reportedly hated Democritus so much that he wished all his books were burned.

Nevertheless, Democritus is considered by some the “ father of modern science “, his approach being closer to science than to philosophy, as was the case of Plato, who is widely cherished to this day.

But while Democritus was close to the truth, his idea was largely ignored for centuries because it was not possible to prove it. However, that changed dramatically in the 20th century, as new scientific discoveries were being made. At some point, philosopher and polymath Bertrand Russel wrote that this atomic theory “was remarkably like that of modern science, and avoided most of the faults to which Greek speculation was prone.”

The atomic theory had once again come to attention.

The Thomson model

Near the end of the 18th century, English researcher John Dalton was struggling to explain some experimental results. Dalton, who also studied color blindness (hence the term “daltonism”), found that no matter how you combine chemical elements, the total mass in the reaction remains the same. He and other chemists also noted that water absorbs different gases in different proportions — for example, water absorbs carbon dioxide far better than it absorbs nitrogen.

He proposed that each chemical element is composed of atoms of a single, unique type. These atoms cannot be altered or destroyed by chemical means, but they can combine to form more complex structures — strikingly similar to what Democritus had proposed.

This was the dominant school of thought for about one century — until one J. J. Thomson came along.

Plum pudding model

Rather ironically, the ‘Plum Pudding Model’ is actually a misnomer. It uses an archaic meaning of the British ‘plum pudding’, which is actually a cake made with raisins (in pre-Victorian times, ‘plum’ was a term used for raisins). But this old-school cake would take yet another meaning.

By the early 1900s, famous researchers such as Amadeo Avogadro, Robert Brown, and even Albert Einstein had explored the flaws of the Dalton model — but couldn’t quite come up with a better alternative. Thomson himself continued to explore the components of the atom and was actively looking for answers.

Atoms were still thought to be the smallest possible division of matter until Thomson’s experiments in 1897. Through experimentation, Thomson found that a cathode ray can be deflected by an electric field. This means that instead of being light, this cathode ray had to be something else, which Thomson correctly deduced to be a flow of electrons. In other words, he had found one of the building blocks of atoms: a negatively charged electron. It was a particle unlike any previously known, and Thomson took this time before he could prove his discovery beyond the shadow of a doubt.

He even measured the mass-to-charge ratio of electrons, finding that they are 1800 times smaller than hydrogen, the smallest atom. There was no doubt about it: atoms were divisible, and these electrons were negative in charge. Which means something must also be positive in atoms.

If you want to bake a plum cake, you must first invent the universe

Atoms are neutral in electric charge. Sure, there are ions that are positively or negatively charged, but technically speaking, atoms are neutral. So if electrons are negative, they must have a positive counterpart.

Since Thomson found electrons to be so small, whatever that positive thing must be should be relatively big. So he considered three scenarios:

• Each negatively charged electron has a positively charged particle that follows it everywhere;
• Electrons orbit a region of positive charge with the same magnitude as the total charge of all electrons;
• The negative electrons occupy a space that is uniformly and positively charged.

He selected the latter as the most likely of the three. He submitted his ideas to the 1904 edition of the  Philosophical Magazine , where Thomson wrote:

… the atoms of the elements consist of a number of negatively electrified corpuscles enclosed in a sphere of uniform positive electrification, …

This theory was embraced by physicists, who started devising experiments to learn even more about atoms, based on this configuration.

Ironically, it was these exact experiments that ended up disproving the Plum Pudding model.

Disproving the cake, and raisin’ a new theory

Funny enough, Thomson’s model was disproved by one of his students, Ernest Rutherford. This just goes to show how influential Thomson’s work and lab were at the time.

Rutherford’s experiments showed that the positive charge is concentrated towards the center of the atom, in what seemed to be an atomic nucleus. This would mean that the negative charge (the electrons) would be concentrated outside of the atom.

Rutherford immediately suspected a planetary model of the atom, where the nucleus is like a star and the electrons orbit around it like planets. But there was a problem, and a big one at that: it contradicted classical mechanics.

In Rutherford’s envisioned model, the electron would release electromagnetic radiation while orbiting a nucleus. This means it would lose energy in the process, spiraling closer to the nucleus, and collapsing on the atom in no time.

This model is a disaster because it would suggest that all atoms are unstable, which is clearly not the case. So the planetary atom model is tempting, but it lacks something fundamental, and was initially disregarded.

It was only when Niels Bohr’s explanation came along that this model could find its ground.

According to Both, the electron is able to revolve in certain stable orbits around the nucleus without radiating any energy, contrary to what classical electromagnetism suggests. Rutherford and Bohr presented their model together, and although our understanding of the atom has changed several times and we’ve learned far more about atomic and subatomic particles, this model is still widely used, at least in non-academic circles.

Bohr’s model was not perfect. Fast forward to modern times and we have a substantially better understanding of atoms, but we’re still trying to reconcile various aspects of atom structure (particularly quantum physics ).

Why bother learning about the Plum Pudding model

It’s easy to disregard the Plum Pudding model as flawed or imperfect and never look at it again. But there’s a reason why physics classes still feature this model, and it’s not just for historical reference.

The idea is that if we want to truly learn something, and not just memorize it, it helps to build a process. If we go through the stages of how physicists first learned about atoms, what theories they had, and how these theories were proven or disproven, we gain a much better understanding. That’s why we learn about the Plum Pudding model, because there can be value even in discredited ideas.

Rest assured: as science and technology progress, no doubt some of the models we use today will turn out to be flawed, and people will still learn about them.

We’re still learning new things about the atoms’ constituents and their structure, and we’ll be learning more for the foreseeable future. Science is rarely about finding an ultimate, finite truth — instead, science is about adding more and more layers of understanding and building approximate models. Thomson’s model was one of these approximations: it was far from perfect, in fact, it was thoroughly disproven — and yet, it played an important role, as it paved the way for more, better discoveries to be made.

This is what science is all about.

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Browse Course Material

Course info.

• Prof. Donald Sadoway

Departments

• Materials Science and Engineering

As Taught In

• Chemical Engineering

Learning Resource Types

Introduction to solid state chemistry, 3. atomic models: rutherford & bohr.

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Session Overview

Prerequisites

Before starting this session, you should be familiar with:

• Session 2: The Periodic Table

Looking Ahead

Prof. Sadoway discusses the atomic spectra of hydrogen ( Session 4 ).

Learning Objectives

After completing this session, you should be able to:

• Understand Thomson’s “plum pudding” model .
• Understand Rutherford’s “nuclear” model .
• Explain the Bohr model of hydrogen .
• Understand Bohr’s quantization condition.

Archived Lecture Notes #1 (PDF) , Sections 1-3

Lecture Video

• Download video
• Download transcript

Lecture Slides (PDF - 9.3MB)

Periodic Table and Table of Constants

Lecture Summary

Prof. Sadoway talks about the principles of modern chemistry and how that led to the understanding of the structure of the atom . He details Bohr’s postulates for the hydrogen atom and discusses how the Planck-Einstein relationship applies to electron transitions. He defines the different isotopes of hydrogen.

This lecture includes the following:

• Electrons are distributed uniformly throughout the atom
• Conclusions from the gold foil experiment
• Majority of the mass is found in the nucleus
• Electrons orbit around the nucleus
• Explanation of blackbody radiation and atomic spectra
• Electrons follow circular orbits around a nucleus
• Orbital angular momentum is quantized hence only certain orbits are possible
• Electrons in stable orbits do not radiate
• Electrons change orbits by radiating or absorbing photons

Problems (PDF)

Solutions (PDF)

Textbook Problems

For Further Study

Supplemental readings.

Ottaviani, J. Suspended in Language: Niels Bohr’s Life, Discoveries, and the Century He Shaped . GT Labs: Ann Arbor, MI, 2004. ISBN: 9780978803728.

Rozental, S. Niels Bohr: His Life and Work as Seen by His Friends and Colleagues . New York, NY: Wiley, 1967.

Bohr, Niels H. D. On the Constitution of Atoms and Molecules . New York, NY: W.A. Benjamin, 1963.

Bohr, Niels H. D. Atomic Physics and Human Knowledge . New York, NY: Wiley, 1958.

Bohr, Niels. “ On the Constitution of Atoms and Molecules. ” Philosophical Magazine Series 6 26 (July 1913): 1-15.

Cathcart, B. The Fly in the Cathedral: How a Small Group of Cambridge Scientists Won the Race to Split the Atom . New York, NY: Penguin, 2005. ISBN: 9780670883219.

Andrade, E. N. Rutherford and the Nature of the Atom . Garden City, NY: Doubleday, 1964.

Frayn, M. Copenhagen: A Play in Two Acts . New York, NY: S. French, 2000.

Miller, D. P. Discovering Water: James Watt, Henry Cavendish and the Nineteenth Century Water Controversy . Burlington, VT: Ashgate, 2004. ISBN: 9780754631774.

Cavendish Laboratory

How Atoms Work

Joseph Thompson - 1906 Nobel Prize in Physics

Ernest Rutherford - 1908 Nobel Prize in Chemistry

Johannes Geiger

Ernest Marsden

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Henry Cavendish

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How does the plum pudding model work?

The ‘plum pudding’ model of the atom was proposed by JJ Thomson, who had also discovered the electron. It was put forth before the discovery of the nucleus. According to this model, the atom is a sphere of positive charge, and negatively charged electrons are embedded in it to balance the total positive charge.

Table of Contents

What did the plum pudding experiment prove?

J.J. Thomson’s experiments with cathode ray tubes showed that all atoms contain tiny negatively charged subatomic particles or electrons. Thomson proposed the plum pudding model of the atom, which had negatively-charged electrons embedded within a positively-charged “soup.”

How JJ Thomson’s plum pudding model disproved Dalton’s atomic theory?

Upon measuring the mass-to-charge ration of these particles, he discovered that they were 1ooo times smaller and 1800 times lighter than hydrogen. This effectively disproved the notion that the hydrogen atom was the smallest unit of matter, and Thompson went further to suggest that atoms were divisible.

Why was the plum pudding experiment inaccurate?

We’ve been looking at how Ernest Rutherford showed that Thomson’s plum pudding (think of Christmas pudding or fruit cake) model of the atom was incorrect by firing alpha particles at a piece of thin gold foil. Although most alpha particles passed straight through, some were scattered at large angles, or even came back.

What is the plum pudding model simple?

The plum pudding model (also known as Thomson’s plum pudding model) is a historical scientific models of the atom. The plum pudding model is defined by electrons surrounded by a volume of positive charge, like negatively-charged “plums” embedded in a positively-charged “pudding” (hence the name).

Is the plum pudding model accurate?

He argued that the plum pudding model was incorrect. The symmetrical distribution of charge would allow all the α particles to pass through with no deflection. Rutherford proposed that the atom is mostly empty space. The electrons revolve in circular orbits about a massive positive charge at the centre.

What disproved plum pudding model?

Answer and Explanation: Rutherford disproved the Plum Pudding Model of the atom by conducting his gold foil experiment. In this experiment, Rutherford tested Thomson’s Plum Pudding Model by attempting to pass a beam of alpha particles through a thin gold foil.

What causes the alpha particles to deflect backwards?

A tiny number of alpha particles, traveling at 10% of the speed of light, hit a dense atomic center right in its middle. The collision and the repulsion cause the alpha particle to “bounce” backwards and move on a very different path. These are the reflected rays .

Why do we no longer use the plum pudding model of atom?

2) Rutherford’s model also showed that there is a very dense positively charged area in the center of atom which was later discovered as the nucleus. And according to Thomson’s model there is no scope for nucleus. These were the reasons which led to rejection of Thomson’s model of atom.

What’s the difference between Dalton’s model and JJ Thomson’s model?

The difference between Dalton’s model of the atom and Thomson’s model was that Dalton’s model had different elements that consist of different atoms and Thomson’s model had atoms that have smaller particles called electrons.

Which of Dalton’s principles were contradicted by JJ Thomson?

Which of Dalton’s principles was contradicted by the work of JJ Thomson? His model realized electrons were interspersed within the atom with positive particles, but didn’t discover that there was a core nucleus with electrons outside it.

What did Thomson’s model of the atom include that Dalton’s didn t?

The Thomson’s model include Electron clouds that ‘Dalton’s model’ did not have. Explanation: Thomson’s Model: The atom has been composed of several electrons that are surrounded by a collection of positive charge in order to balance the negative charged electrons.

How was Rutherford’s gold foil experiment inconsistent with the plum pudding model of the atom?

The results of the experiment were inconsistent with the plum-pudding model of the atom, in which the atom was viewed as tiny electrons embedded in a dispersed pudding of positive charge. Rutherford proposed that the positive charge must really be localized, concentrated in a small nucleus.

Is the plum pudding model neutral?

Thomson’s model (1897) J.J. Thomson discovered the electron . Atoms are neutral overall, so in Thomson’s ‘plum pudding model’: atoms are spheres of positive charge.

How did JJ Thomson discover electrons?

In the year 1897 J.J. Thomson invented the electron by playing with a tube that was Crookes, or cathode ray. He had shown that the cathode rays were charged negatively. Thomson realized that the accepted model of an atom did not account for the particles charged negatively or positively.

Why is it called a plum pudding?

This goes back to the Victorian practice of substituting dried plums with other dried fruits, such as raisins. Dried plums or prunes were so popular that any goods which contained dried fruits were referred to ‘plum cakes’ or ‘plum puddings’.

Why did JJ Thomson Use plum pudding?

Thomson realized that the accepted model of an atom did not account for negatively or positively charged particles. Therefore, he proposed a model of the atom which he likened to plum pudding. The negative electrons represented the raisins in the pudding and the dough contained the positive charge.

What is also called plum pudding?

The plum pudding model (also known as Thomson’s plum pudding model) is a historical scientific model of the atom. The plum pudding model is defined by electrons surrounded by a volume of positive charge, like negatively-charged “plums” embedded in a positively-charged “pudding” (hence the name).

What’s the difference between plum pudding model and atom?

So the plum pudding model is different from the hard-sphere model of the atom because in the hard sphere model of the atom, the atom is the smallest division of matter. But in the plum pudding model, there is a negatively charged electron which is smaller than an atom.

What are the differences between the plum pudding model and the nuclear model?

The plum pudding model is an early attempt to show what an atom looks like. Bombardment of gold foil with alpha particles showed that some particles were deflected. The nuclear model of the atom consists of a small and dense positively charged interior surrounded by a cloud of electrons.

What is the hypothesis of Thomson’s atomic model?

The Plum Pudding Model He hypothesized that the rest of the atom must be positively charged in order to cancel out the negative charge of the electrons.

Does light pass through gold?

Transmitted color of gold Gold is so malleable that it can be beaten into gold leaf less than 100 nm thick, revealing a bluish-green color when light is transmitted through it. Gold reflects yellow and red, but not blue or blue-green.

Why can alpha particles penetrate gold?

Why did Rutherford use gold as his target?

Why did Rutherford select a gold foil in his α–ray scattering experiment? Answer: Rutherford used gold for his scattering experiment because gold is the most malleable metal and he wanted the thinnest layer as possible. Therefore, Rutherford selected a Gold foil in his alpha scattering experiment.

Why was Thomson’s model not accepted?

But after performing Rutherford’s gold foil experiment, it was concluded that most of the space inside an atom is empty because most of the alpha particles pass straight through without getting deflected which was contrary to what has been predicted by Thomson’s model. Hence, Thomson’s model of an atom was rejected.

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Thomson’s Atomic Model

Thomson’s Atomic Model is one of the fundamental models of the atom that tries to explain the working and structure of the atom. this model was proposed by famous Scientist JJ Thomson in 1904. Thomson during his cathode ray experiment proved the existence of a negatively charged particle called electron that exists inside the atom. And after complaining about his result he prosed the Thomson atomic model also called Pulm Pudding Model. 

In this article, we will learn more about, Thomson Atomic Model, its postulate, and its limitations in detail. 

Thomson’s Atomic Model was proposed by J.J. Thomson in 1904, following his discovery of the electron in 1897 after his famous cathode ray experiment. The model is also known as the Plum Pudding Model. In this model, Thomson proposed that atoms are composed of a positively charged sphere with negatively charged electrons embedded within it. The positive charge of the sphere was thought to be uniformly distributed to balance out the negative charge of the electrons. The electrons were held in place by electrostatic attraction to the positive sphere.

The model explained certain experimental observations of that time that atoms were electrically neutral and that cathode rays were negatively charged. The atomic model was later discarded as it was unable to explain the various results concluded by various scientists after their experiments such as it was unable to explain the existence of the nucleus whose existence was confirmed by Rutherford in his experiment.

Plum Pudding Model

Thomson Atomic Model is also called the Plum Pudding model as it represents the Plum Pudding. According to Thomson, an atom represents a sphere of radius of magnitude in Angstrom. (10 -10 ). In this sphere, the positive charge is spread uniformly and the negative charge is embedded in this positive charge due to electrostatic attraction between the charge. The magnitude of the positive and the negative charge in the sphere is equal according to Plum Pudding Model.

Observations of Thomson’s Atomic Model

Thomson’s Atomic Model, also called the Plum Pudding Model states that an atom can be compared to a plum pudding where electrons are like dry fruits in a sphere of positive charge, representing the pudding. We can also compare this with a watermelon where the positive charge is comparable to the edible part of the watermelon, and electrons are like seeds that are embedded in that sphere.

The diagram explaining the Plum Pudding Model or the Thomson Atomic model is added below which shows that positive charge is spread throughout the atom and negative charge is embedded in the atom maintaining the electrical neutrality of the atom.

Postulates of Thomson’s Atomic Model

Various Postulates of Thomson’s Atomic Model are mentioned below:

An atom consists of a positively charged sphere or cloud in which negatively charged electrons are embedded. The positive charge of the sphere is uniformly distributed to balance the negative charge of the electrons. An atom is an electrically neutral quantity and the total positive charge of the atom is balanced by the total negative charge in the atom.

Thomson’s model is also called Plum Pudding Model or Watermelon Model.

Limitations of Thomson’s Atomic Model

Thomson’s atomic model had several limitations that were eventually overcome by further research and the experiments of various scientists later on. Some of the limitations of Thomson’s Atomic Model are:

This model did not account for the presence of positively charged particles in the atom, which were later identified as protons by Ernest Rutherford. The model assumed that the positive charge was distributed uniformly throughout the atom. The model could not explain the results of the gold foil experiment conducted by Rutherford, which showed that most of the mass and positive charge of an atom is concentrated in a small, dense nucleus at the centre of the atom. The model could not explain the phenomenon of atomic spectra, which is the emission and absorption of specific wavelengths of light by atoms. The model did not explain the presence of Isotopes.

Despite these limitations, Thomson’s Atomic Model is an important step in the development of Atomic Theory and only after this theory, there came various theories that provide a better understanding of Atoms.

Background of Thomson’s Atomic Model

The first scientific discussion about the structure of atoms was started by famous scientist JJ Thompsom in 1897. He stated that atoms are spherical shape objects in which electrons are embedded in a jelly-like substance and the jelly-like substance is called protons. Initially, scientists are of the view that atoms are indivisible and they did not believe the explanation of Thomson stating that atoms are made up of smaller particles. This was proved later by his cathode ray experiment which proved that atoms are made up of negatively charged particles called Electrons.

Thomson Atomic Model is not the most accurate model to explain the structure of an atom as it has various drawbacks but it was the first model to explain the basic structure of an atom that atom as a whole is neutral and it consists of positive and negative charge in equal magnitude. After Thomson, various scientists proposed the atomic structure which was further enhanced to get the idea of the atom which prevails today.

Bohr’s Model of an Atom Rutherford’s Atomic Model Dalton’s Atomic Theory

FAQs on Thomson’s Atomic Model

Q1: what is thomson’s atomic model.

Thomson’s Atomic Model was the first model to explain the basic structure of the atom. It was given by famous scientist JJ Thomson after the discovery of electrons from his cathode ray experiment. He claimed that atoms are made up of electrons and protons and the electrons are embedded in the continuous spread of protons as the pulm is spread in the pudding. Hence this model is also called the Pulm-Pudding model, according to him atom is electrically neutral and the magnitude of positive and negative charges are equal.

Q2: Which Model best explains Atom’s Neutrality?

Thomson’s Atomic Model was the one which first explains that as a whole an atom is an electrically neutral entity. He states that the magnitude of the negative charge (electrons) and the magnitude of the positive charge (protons) are equal in an atom.

Q3: What are the major Drawbacks of Thomson’s Model?

Various drawbacks of Thomson’s Atomic Model are, It fails to explain the existence of the neutrons that were discovered by Chadwick. It fails to explain the finding of Rutherfor’s Gold Foil experiment. It does not explain the existence of isoelectric species, etc.

Q4: What are the Important Features of Thomson Atomic Model?

The important features of the Thomson Atomic model are, It was the first model to think that atom is like a sphere. It successfully explains the neutrality of the atom. It explains that the magnitude of positive and negative charges in an atom is equal.

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