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Democritus
He thought that all things were made of tiny, invisible, indestructible particles, called atoms. Thought atoms varied in size, shape and weight. -
Robert Boyle
In his book The Sceptical Chymist, Boyle attacked Aristotle’s and Paracelsus’s theories. He proposed that elements are basically composed of ‘corpuscles’ of various sorts and sizes capable of organising themselves into groups and that each group constitutes a chemical substance.He clearly distinguished between mixtures and compounds and showed that a compound can have very different properties from those of its constituents. This prefigured the atomic theory of matter. -
John Dalton
He came up with an atomic theory that stated; 1) All matter is made of atoms. Atoms are indivisible and indestructible.
2) All atoms of a given element are identical in mass and properties
3) Compounds are formed by a combination of two or more different kinds of atoms.
4) A chemical reaction is a rearrangement of atoms. -
Joseph John Thomson
He discovered electrons in an investigating of a long-standing puzzle known as "cathode rays." He dicovered that the rays were negitively charged particles known as electrons even smaller than atoms. -
Albert Einstein
He published a paper that pointed toward a crucial test of the reality of atoms. he also devised a matematical method of calculating the size of atoms and molecules from an analysis of sugar molecules. -
Ernest Rutherford
he discovered the nucleus and protons by performing the gold foil experiment which is positively charged particles are shot through a gold foil and some were reflected back indicating a small positively charged mass. In his theory it states that most of an atom is empty space. He came to a conclusion that there was a positive particle in the nucleus known as the proton. -
Niels Bohr
This theory established the first sound description of the behavior of electrons on atoms. His theory is an extension of rutherfords description. the electrons orbit around the nucleus, each electron orbits at a different distances. -
Louis de Broglie
He proposed that electrons have a wave nature and a wavelength.deBroglie proposed that all material objects have a wave nature. -
Erwin Schrodinger
He took Bohr's model a step further by using 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. Unlike the Bohr model, the quantum mechanical model does not define the exact path of an electron, but, predicts the odds of the location of the electron. -
Heisenberg
The uncertainty principle is the more precisely the position is determined, the less precisely the momentum is known in this instant, and vice versa. -
James Chadwick
He discovered neutrons in an invisible game of billiards. He fired the neutrons at a block of paraffin wax, which has a high concentration protons. Some of the neutrons collided with protons in the wax and knocked them out. Chadwick could then detect and measure their energy. Using his knowledge of energy and momentum, he detected that the neutrons had slightly more mass than protons. -
Aristotle
Opposed Democritus' theory now known as the "Atomic Theory" by stating that matter was made of air, water, fire, and earth.