REPORT: HISTORICAL DEVELOPMENT OF ATOMIC MODELSSCIENTISTSDemocritus:He was born in Greece, 460BC. He was a philosopher. Democritus studied about mathematics, biology, geography, astrology, economy and sociology.
He had an idea what is the smallest piece of matter. Democritus thought if you continue cut the stone into smaller pieces, at one point you can’t cut because it is too small. He called that piece “atomos”, meaning “indivisible”. For him, atomos can not be divisible or destroyed. However, Democritus did not do any experiments. Democritus was the first person that used the word atom.
He died in 360BC.John Dalton: John Dalton was born on 6th of September 1766, in Eaglesfield, England. He was meterologist, chemist and physicist. He had an atomic theory. He said all matter is made up of tiny particles called atoms, all atoms of a given element are similar to one another and different from atoms of other elements, atoms of two or more different elements combine to form compounds. A particular compound is always has the same number of each kind of atom and atoms are never created or destroyed during a chemical reaction. He based his theory with more on experimentation than pure reason.
That’s why he was different from Democritus. He also studied about “colour blindness” the illness which known “Daltonism”. He found a law of conservation of mass. He died on July 27, 1844 Manchester, England.Joseph John Thomson: Joseph John Thomson was born in Cheetham Hill on December 18, 1856. J.J. Thomson graduated from Owens College.
He was a professor on Cambridge University. In 1897, J. J. He applied electricity to a glass tube, which produced streams of small particles called cathode rays Because these rays were attracted to a positively charged electrode, Thomson realized that the particles in rays must be negatively charged.
So he discovered the electrons by using Cathode Ray Tube. J. J Thomson called electrons corpuscles. He published “Application of Dynamics to Physics and Chemistry” “Elements of the Mathematical Theory of Electricity and Magnetism.” and “Notes on Recent Researches in Electricity and Magnetism”, He had an atomic model which known “Thomson’s Plum Pudding Model”.
It proposed in 1904. He was selected Royal Society in 1884. He published lots of books and won a lot of prizes. In 1906, he received Noble Prize. Thomson died on August 30, 1940. Ernest Rutherford: Ernest Rutherford was born on August 30, 1871, in Nelson, New Zealand. He had five sisters and six brother. He graduated from Canterbury College.
He was research student at the Cavendish Laboratory under J.J. Thomson. In the meantime they tested the model with J.J.
Thomson in 1911. In Rutherford’s experiment positively charged particles were imed at a thin sheet of gold foil. Rutherford was suprised to find that some particles were deflected as they passed through the gold foil. From the gold-foil experiments, Rutherford realized that the protons must be contained in a small, positively charged region at the center of the atom, which he called the nucleus. Rutherford published several books: Radioactivity (1904); Radioactive Transformations (1906). He was elected Fellow of the Royal Society in 1903.
He married with Mary Newton. They had a child. He died in Cambridge on October 19, 1937. Niels Bohr:Bohr was born in Copenhagen on October 7, 1885. His father was a famous medicine professor.
He has also a brother who graduated from Copenhagen University. His brother was a mathematic professor. Niels Bohr had six sons. He left for England to begin postdoctoral work under J.
J. Thomson. After a few months, he left Cambridge to join Ruthherford at Manchester. In 2013, Bohr thought about electrons orbit around the atomic nucleus. He suggested that electron orbits were at a fixed a fixed energy orbit referred as an energy level.
During his life, Niels Bohr received a lot of medals of honour and also he received Noble prize in 1922. He has a very famous quote: “If quantum mechanics hasn’t profoundly shocked you, you haven’t understood it yet.” Niels Bohr died in Copenhagen on November 18, 1962.Democritus’s Atomic Model:This is Democritus’ atomic theory exactly:All matter consists of invisible particles called atoms.Atoms are indestructible.Atoms are solid but invisible.Atoms are homogenous.
Atoms differ in size, shape, mass, position, and arrangement.Solids are made of small, pointy atoms.Liquids are made of large, round atoms.Oils are made of very fine, small atoms that can easily slip past each other. This was Democritus’ atomic model.
It was simply a round sphere with no electrons, protons, or neutrons. Democritus created the first atomic model. His contribution helped people with understanding the idea of an atom, and helped other scientists further look into the science of the atom and its generic makeup.Dalton’s Atomic ModelDalton’s atomic theory was the first complete attempt to describe all matter in terms of atoms and their properties.Dalton based his theory on the law of conservation of mass and the law of constant composition.The first part of his theory states that all matter is made of atoms, which are indivisible.The second part of the theory says all atoms of a given element are identical in mass and properties.The third part says compounds are combinations of two or more different types of atoms.
The fourth part of the theory states that a chemical reaction is a rearrangement of atoms.Parts of the theory had to be modified based on the discovery of subatomic particles and isotopes.Thomson’s Atomic Model: Rutherford’s Atomic Model:Rutherford atomic model, also called nuclear atom or planetary model of the atom, description of the structure of atoms proposed (1911) by the New Zealand-born physicist Ernest Rutherford. The model described the atom as a tiny, dense, positively charged core called a nucleus, in which nearly all the mass is concentrated, around which the light, negative constituents, called electrons, circulate at some distance, much like planets revolving around the Sun.Niels Bohr’s Atomic Model:Bohr atomic model, description of the structure of atoms, especially that of hydrogen, proposed (1913) by the Danish physicist Niels Bohr. The Bohr model of the atom, a radical departure from earlier, classical descriptions, was the first that incorporated quantum theory and was the predecessor of wholly quantum-mechanical models.
The Bohr model and all of its successors describe the properties of atomic electrons in terms of a set of allowed (possible) values. Atoms absorb or emit radiation only when the electrons abruptly jump between allowed, or stationary, states. Direct experimental evidence for the existence of such discrete states was obtained (1914) by the German-born physicists James Franck and Gustav Hertz.f) Modern Electron Cloud Atomic ModelA German scientist named Werner Heisenberg proposed the idea of the electron cloud model in 1927.
It is the most recent model of the atom. Notice that instead of showing the paths of the orbit of the electrons it just shows a “cloud” around the nucleus. The cloud represents where any one electron could be at any time. This electron cloud model is based on quantum mechanics.
