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460
Democritus
460 BC - 370 BC. His theory told everyone that everything is made of atoms and they’re invisible but solid. They’re indestructible and always differ in shape, size, mass, position and arrangement. And then the solids are made of atoms that are pointy and small, liquids made of round and large one, and oils are made of small and fine atoms. -
Joseph Proust
1754-1826 Made up the Law of Definite Proportions which is ‘The law of definite proportions states samples of a compound will always contain the same proportion of elements by mass’. Which is also known as ‘Proust’s Law’. -
John Dalton
1766-1844 John was best known for his atomic theory. His theory consisted of five steps: -All matter consists of tiny particles.-Atoms are indestructible and unchangeable-Elements are characterized by the mass of their atoms-When elements react, their atoms combine in simple, whole-number ratios-When elements react, their atoms sometimes combine in more than one simple, whole-number ratio. -
G.J. Stoney
1826-1911 He said that electricity was made of small negative particles called electrons. -
Dmitri Mendeleev
1834-1907 He arranged cards to make sure they matched up with the element name, atomic mass, and physical and chemical properties, which formed the Periodic Table. -
J.J. Thomson
1856-1940 He discovered the theory of atoms having positive and negative particle. And then discovered electrons, the theory that atoms are spheres, and that they were not invisible -
Emest Rutherford
1871-1937 Ernest’s theory was that the electrons circled the nucleus, and that the nucleus was made up of neutrons (negative/ uncharged particles) and protons (positively charged particles). He discovered this when he threw alpha particles and a thin sheet of gold and that the particles passed through but in the middle they would either change direction or bounce back. -
Neils Bohr
1885- 1962 Adding quantum theory to Rutherford’s atomic theory, he thought that the electrons orbit the nucleus according to where the other electrons were and their angles, and the amount of electrons per shell. -
H.G.J. Moseley
1887-1915 Made Moseley’s law which is ‘the observed law that the square root of the frequencies of lines in atomic x-ray spectra depends linearly on the atomic number of the emitting atom.’ -
James Chadwick
1891-1974 He guessed that atoms have neutrons, and that the atomic number is the same as the protons
