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Scientists Who Developed Atomic Theory

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on 25 March 2014

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Transcript of Scientists Who Developed Atomic Theory

Ernest Rutherford
He discovered that an atom has a very tiny, and dense, positively charged nucleus in its center, with electrons orbiting around the outside of the nucleus. He did so during his famous gold foil experiment. In this experiment, Rutherford shot very small alpha particles into an extremely thin piece of gold, and by using special equipment, was able to tell if the particles went through the gold, or bounced off of it. Since most of the particles went through, and very few particles bounced off, he was able to come to the conclusion that there is a tiny, positive nucleus in each atom, with electrons moving around the nucleus. He also realized that between the electrons and nucleus is empty space.
H.G.J. Moseley
Using x-ray tubes, he was able to find the charges of the nuclei in most of the atoms on the periodic table. He also wrote that the atomic number of an element is equal to the number of protons in the nucleus of that atom. This information was used to reorganize the periodic table so that it was based on the atomic number of an element rather than its atomic mass. This meant that the elements were more accurately positioned on the table. Many people believe that if he had not died so early in his life (he was only 27), then he would have been able to contribute a lot more to atomic theory.
Niels Bohr
He discovered that electrons travel in separate orbits around the nucleus which are sometimes called shells. He also found out that the number of electrons that orbit the nucleus determine the properties of an atom. Bohr also realized that each shell has a specific number of electrons depending of how close or far a shell is from the nucleus. These shells can also called "electron clouds". He developed the Bohr-Rutherford diagram which is a model that is still used today when diagramming an elements atom. This type of diagram shows how many protons and neutrons are in the nucleus. It also displays how many electrons and shells makeup an atom. He earned a Nobel Prize for this research and the element Bohrium (Bh) was named in his honor.
James Chadwick
He discovered the neutron and was able to prove that neutrons, along with protons, form the nucleus of an atom. Working along side with Ernest Rutherford, Chadwick realized that in every element, the atomic mass was greater than the atomic number. This meant that there was something else in the atom that was making its atomic mass greater than the number of protons and electrons in the atom. Chadwick realized that it was a particle with no charge, called a neutron. This discovery earned him the 1935, Nobel Prize in Physics.
John Dalton
J.J. Thompson
He discovered the electron. Through experimentation, he realized that atoms are made up of even smaller positive and negatively charged parts. Today we call these parts protons, which are positive, and electrons, which are negative. What Thompson thought an atom looked like is the plum pudding model. In this model, the raisins in the pudding represented the electrons, and the pudding represented the positively charged protons in an atom. This model was created before the discovery of the nucleus by Ernest Rutherford in 1911. In 1906, J.J. Thompson won the Nobel Prize in Physics for his discovery of the electron
Many people consider him the first scientist to study modern atomic theory. He was one of the first scientists since ancient times to reconsider the idea that everything is made up of atoms and that every element is made out of an atom that is slightly different from other atoms that make up other elements. He also created one of the first drafts of the periodic table of elements which included carbon, iron, and oxygen. In this table, every element had a different symbol within a circle. Dalton's Atomic theory was that:
1) Atoms make up all matter and cannot be broken down further.
2) Every element has a different atom with different properties,
3) Atoms of different elements can be put together to create new substances.
4) All of an elements atoms have identical properties.
While Dalton's Theory was mostly correct, some of the elements on the table could actually be broken down further and therefore were not actually elements.
J.J. Thompson
John Dalton
Ernest Rutherford
H.G.J Moseley
James Chadwick
Niels Bohr
Scientists Who Developed Atomic Theory
Dalton's Periodic Table of Elements
Thompson's idea
of an atom.
Elements are now sorted by
Atomic number on the periodic
table because of Moseley's work.
Rutherford's Gold Foil Experiment
Bohrium element named after Niels Bohr.

James Chadwick
Chadwick's model of the atom
The End!
Full transcript