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400
Democritus
Democritus questioned if matter could be divided forever. His theory was that matter could not be divided forever but his theory was ignored because of unanswered questions and higher authority in that field. People such as Aristotle and Plato disagreed with his work and so did the people. -
Antoine Lavosier
Lavosier developed the Law of Conservation of Mass.
This law said that elements were pure substances and cannot be broken down -
John Dalton
In 1803 English chemist John Dalton proposed the atomic theory and came up with 4 postulates
1) Each element is composed of extremely small particles called atoms
2)All atoms of a given element are identical, but they differ from those of any other element.
3)Atoms are neither created nor destroyed in any chemical reaction
4)A given compound always has the same relative numbers and kinds of atoms -
Michael Faraday
Michael Faraday studied the effect of electricity on solutions -
Dmitri Mendeleev
Dmitri created the first periodic table. -
Sir William Crookes
Crookes discovered many things about the cathode ray. He discovered that the rays move in a straight line, that it causes glass to illuminate and many more. -
W.K Roentgen
Wilhelm Roentgen discovered x-rays -
Henri Becquerel
Henri Becquerel discovered radioactivity -
J.J Thomson
J.J proposed that there was something smaller in size compared to an atom. He was correct and it was electrons. J.J discovered electrons. -
J.J. Thomson
J.J proposed that there was something smaller in size compared to an atom. He was correct and it was electrons. J.J discovered electrons. -
The Curies
They discovered the radioactive elements radium and polonium -
Max Planck
He developed the idea of quanta which is a discrete unit of energy -
Albert Einstein
Einstein discovered the relationship between energy and mass -
Hans Geiger
He invented the Geiger counter which counts alpha particles -
Robert Milliken
His oil drop experiment determined the mass and charge of an electron -
Ernest Rutherford
Ernest discovered the proton and the nucleus of the atom. -
Ernest Rutherford
Ernest discovered the proton and the nucleus of the atom. -
Neils Bohr
He claimed that electrons are arranged in circular orbits around the nucleus -
Erwin Schrodinger
He introduced wave mechanics -
James Chadwick
He discovered the neutron -
Enrico Fermi
He created the chain reaction for the atomic bomb