Jj thomson atomic theory year

First modern model of the atom

The plum pudding model is an obsolete scientific model of the atom. It was first proposed by J. J. Thomson in 1904 following his discovery of the electron in 1897, and was rendered obsolete by Ernest Rutherford's discovery of the atomic nucleus in 1911. The model tried to account for two properties of atoms then known: that there are electrons, and that atoms have no net electric charge. Logically there had to be an equal amount of positive charge to balance out the negative charge of the electrons. As Thomson had no idea as to the source of this positive charge, he tentatively proposed that it was everywhere in the atom, and that the atom was spherical. This was the mathematically simplest hypothesis to fit the available evidence, or lack thereof. In such a sphere, the negatively charged electrons would distribute themselves in a more or less even manner throughout the volume, simultaneously repelling each other while being attracted to the positive sphere's center.

Despite Thomson's efforts, his model couldn't account for emission spectra and valencies. Based on experimental studies of alpha particle scattering (in the gold foil experiment), Ernest Rutherford developed an alternative model for the atom featuring a compact nucleus where the positive charge is concentrated.

Thomson's model is popularly referred to as the "plum pudding model" with the notion that the electrons are distributed uniformly like raisins in a plum pudding. Neither Thomson nor his colleagues ever used this analogy. It seems to have been coined by popular science writers to make the model easier to understand for the layman. The analogy is perhaps misleading because Thomson likened the positive sphere to a liquid rather than a solid since he thought the electrons moved around in it.

Significance

Thomson's model was the first atomic model to describe an internal structure. Before this, a

English physicist (1856–1940)

This article is about the Nobel laureate and physicist. For the moral philosopher, see Judith Jarvis Thomson.

Sir Joseph John Thomson (18 December 1856 – 30 August 1940) was an English physicist who received the Nobel Prize in Physics in 1906 "in recognition of the great merits of his theoretical and experimental investigations on the conduction of electricity by gases."

In 1897, Thomson showed that cathode rays were composed of previously unknown negatively charged particles (now called electrons), which he calculated must have bodies much smaller than atoms and a very large charge-to-mass ratio. Thomson is also credited with finding the first evidence for isotopes of a stable (non-radioactive) element in 1913, as part of his exploration into the composition of canal rays (positive ions). His experiments to determine the nature of positively charged particles, with Francis William Aston, were the first use of mass spectrometry and led to the development of the mass spectrograph.

Thomson was awarded the 1906 Nobel Prize in Physics for his work on the conduction of electricity in gases. Thomson was also a teacher, and seven of his students went on to win Nobel Prizes: Ernest Rutherford (Chemistry 1908), Lawrence Bragg (Physics 1915), Charles Barkla (Physics 1917), Francis Aston (Chemistry 1922), Charles Thomson Rees Wilson (Physics 1927), Owen Richardson (Physics 1928) and Edward Victor Appleton (Physics 1947). Only Arnold Sommerfeld's record of mentorship offers a comparable list of high-achieving students.

Education and personal life

Joseph John Thomson was born on 18 December 1856 in Cheetham Hill, Manchester, Lancashire, England. His mother, Emma Swindells, came from a local textile family. His father, Joseph James Thomson, ran an antiquarian bookshop founded by Thomson's great-grandfather. He had a brother, Frederick Vernon T

On April 30, 1897, British physicist J.J. Thomson announced his discovery that atoms were made up of smaller components. This finding revolutionized the way scientists thought about the atom and had major ramifications for the field of physics. Though Thomson referred to them as "corpuscles," what he found is more commonly known today as the electron.

Mankind had already discovered electric current and harnessed it to great effect, but scientists had not yet observed the makeup of atoms. Thomson, a highly-respected professor at Cambridge, determined the existence of electrons by studying cathode rays. He concluded that the particles making up the rays were 1,000 times lighter than the lightest atom, proving that something smaller than atoms existed. Thomson likened the composition of atoms to plum pudding, with negatively charged "corpuscles" dotted throughout a positively-charged field.

The plum pudding analogy was disproved by Ernest Rutherford, a student and collaborator of Thomson’s, in Thomson's lab at Cambridge in 1910. Rutherford's conclusion that the positive charge of an atom resides in its nucleus established the model of the atom as we know it today. In addition to winning his own Nobel Prize, Thomson employed six research assistants who went on to win Nobel Prizes in physics and two, including Rutherford, who won Nobel Prizes for chemistry. His son, George Paget Thomson, also won a Nobel Prize for his study of electrons. Combined with his own research, the network of atomic researchers Thomson cultivated gave humanity a new and detailed understanding of the smallest building blocks of the universe.

Sir Joseph John Thomson or J.J. Thomson is best known as the man who discovered the electron.

J.J. Thomson Biographical Data

Tomson was born December 18, 1856, Cheetham Hill, near Manchester, England. He died August 30, 1940, Cambridge, Cambridgeshire, England. Thomson is buried in Westminster Abbey, near Sir Isaac Newton. J.J. Thomson is credited with the discovery of the electron, the negatively charged particle in the atom. He is known for the Thomson atomic theory.

Many scientists studied the electric discharge of a cathode ray tube. It was Thomson's interpretation that was important. He took the deflection of the rays by the magnets and charged plates as evidence of "bodies much smaller than atoms." Thomson calculated these bodies had a large charge-to-mass ratio and he estimated the value of the charge itself. In 1904, Thomson proposed a model of the atom as a sphere of positive matter with electrons positioned based on electrostatic forces. So, he not only discovered the electron but determined it was a fundamental part of an atom.

Notable awards Thomson received include:

• Nobel Prize in Physics (1906) "in recognition of the great merits of his theoretical and experimental investigations on the conduction of electricity by gases" 
• Knighted (1908)
• Cavendish Professor of Experimental Physics at Cambridge (1884–1918)

Thomson Atomic Theory

Thomson's discovery of the electron completely changed the way people viewed atoms. Up until the end of the 19th century, atoms were thought to be tiny solid spheres. In 1903, Thomson proposed a model of the atom consisting of positive and negative charges, present in equal amounts so that an atom would be electrically neutral. He proposed the atom was a sphere, but the positive and negative charges were embedded within it. Modern scientists understand atoms consist of a nucleus of positively-charged protons and neutral neutrons, with nega