-
465 BCE
Democritus-- 465 BC Democritus' atomic theory
(1)all matter is composed of atoms that are invisible(2) there is a void, which is empty space between atoms(3)atoms are completely solid(4) atoms have no internal structure(5)atoms are different in their sizes, shapes, and weight. He created the first atomic model. Simply a round sphere with no electrons, protons, or neutrons. 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. -
56 BCE
Lucretius— 56 BC
Influential works by Lucretius was his didactic poem, “De rerum natura” (On the Nature of Things). Influenced by Democritus. They are all made of the same material, and have no properties other than shape, size, and weight; their weight is the cause of their natural motion downward through the void. This discovery led to scientists’ curiosities of this natural phenomena. -
Antoine Lavoisier 1743-1794
Founder of modern chemistry,found that mass is conserved in a chemical reaction. The total mass of the products of a chemical reaction is always the same as the total mass of the starting materials. This led to one of the fundamental laws of chemical behavior:law of conservation of matter. He invented a system of naming chemical compounds that were made up of multiple element,system is still in use. He started the conversation of what atoms were actually made of. -
John Dalton (1766-1844)
His atomic theory stated an element is pure because all atoms of an element are identical. All the atoms that make up the element have the same mass. All elements are different from each other due to differing masses.1The elements are made of atoms, which are tiny particles, too small to see.2 All atoms of a particular element are identical.3 Atoms of different elements have different properties:their masses are different and their chemical reactions are different.This is still in modern theory. -
J.J. Thompson (1856-1940)
J.J. Thomson discovered electrons and noticed that an atom can be divided. He concluded atoms are made of positive nucleus and negatively charged particles inside them. He developed the Plum Pudding Model. This model shows that the electrons are surrounded by a "pudding" of positive charges to balance the negative charges. J.J. Thomson's discoveries have helped people to have a better understanding of the atom and its generic makeup. -
Ernst Rutherford (1871–1937)
He deciphered the structure of the inside of atom. When alpha particles are fired into gas atoms, a few are violently deflected, which implies a dense, positively charged central region containing most atomic mass. Rutherfords discoveries allowed of the modern atomic model. -
James Chadwick (1891-1974)
James Chadwick bombarded beryllium atoms with alpha particles. An unknown radiation was produced. Chadwick interpreted this radiation as being composed of particles with a neutral electrical charge and the approximate mass of a proton.With the discovery of the neutron, an adequate model of the atom became available to chemists.
