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460 BCE
Democritus
According to Democritus' atomic theory, the universe and all matter obey the following principles: Everything is composed of “atoms”, which are physically, but not geometrically, indivisible. Between atoms, there lies empty space. Atoms are indestructible. -
340 BCE
Aristotel
Aristotle did not believe in the atomic theory, he taught so otherwise. He thought that all materials on Earth were not made of atom. , he believed that they were made of the four elements, Earth, Fire, Water, and Air. He also believed that all substances were made of small amounts of these four elements of matter. -
Period: 340 BCE to
The History of the Atomic Model
Science :) -
Dalton
Dalton's atomic theory proposed that all matter was composed of atoms, indivisible and indestructible building blocks. While all atoms of an element were identical, different elements had atoms of differing size and mass. -
Mendeleev
Mendeleev is known for his work on the Periodic Law and creation of the first Periodic table. In 1869, he created the first Periodic Table. The Periodic Law states that when elements are arranged according to their atomic number, elements with similar properties will appear at regular intervals. -
Stoney
Stoney proposed the particle or atom of electricity to be one of three fundamental units on which a whole system of physical units could be established. George Johnstone Stoney was acknowledged for his contribution to developing the theory of electrons by H.A. Lorentz , in his Nobel Lecture in 1902. -
Thomson
Thomson discovered the electron by experimenting with a Crookes, or cathode ray, tube. He demonstrated that cathode rays were negatively charged. In addition, he also studied positively charged particles in neon gas. -
Nagaoka
Nagaoka proposed an alternative planetary model of the atom in which a positively charged center is surrounded by a number of revolving electrons, in the manner of Saturn and its rings. Nagaoka's model made two predictions: a very massive atomic center (in analogy to a very massive planet) -
Millikan
Millikan began a series of experiments to determine the electric charge carried by a single electron. He began by measuring the course of charged water droplets in an electric field. He later found that all of the drops had charges that were simple multiples of a single number, the fundamental charge of the electron. -
Rutherford
Rutherford proposed that an atom is composed of empty space mostly with electrons orbiting in a set, predictable paths around fixed, positively charged nucleus. -
Bohr
Niels Bohr proposed a theory for the hydrogen atom based on quantum theory that energy is transferred only in certain well defined quantities. Electrons should move around the nucleus but only in prescribed orbits. When jumping from one orbit to another with lower energy, a light quantum is emitted. -
Modern Atomic Model
The modern atomic theory states that atoms of one element are the same, while atoms of different elements are different, this number of protons are so important to the identity of an atom that is called the atomic number, the number of protons in an atom of the element. -
Aston
English chemist Frederick Soddy had ” postulated” that certain elements might exist in forms that he called isotopes that differ in atomic weight while being indistinguishable and inseparable chemically. ... Aston's achievement is illustrated by the fact that he discovered 212 of the 287 naturally occurring isotopes. -
Schrodinger
Erwin Schrödinger, an Austrian physicist, took the Bohr atom model one step further. Schrödinger used mathematical equations to describe the likelihood of finding an electron in a certain position. This atomic model is known as the quantum mechanical model of the atom. -
Chadwick
James Chadwick played a vital role in the atomic theory. He discovered the Neutron in atoms. Neutrons are located in the center of an atom, in the nucleus along with the protons. They have neither a positive nor negative charge, but contribute the the atomic weight with the same effect as a proton. -
Fermin
He proposes a theory of the emission of ss-rays, based on the hypothesis. It was first proposed by Pauli, of the existence of the neutrino.The Nobel Prize for Physics was awarded to Fermi for his work on the artificial radioactivity produced by neutrons, and for nuclear reactions brought about by slow neutrons.
