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400 BCE
Democritus
Democritus was the first person ever to propose that matter was made of atoms, and that they are indestructible. He thought that the solidness of a substance would correspond with the shape and properties of the atoms involved. -
400 BCE
Democritus
Everything is composed of “atoms”, which are physically, but not geometrically, indivisible. Between atoms, there lies empty space,
atoms are indestructible, Atoms have always been, and always will be, in motion . There is an infinite number of atoms, and kinds of atoms, which differ in shape, and size. -
John 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. -
John 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. -
Sir J.J. Thomson
J.J. 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. -
Sir J.J. Thomson
J.J. 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. -
Lord Rutherford
Rutherford designed an experiment to use the alpha particles emitted by a radioactive element as probes to the unseen world of atomic structure. -
Niels Bohr
Niels Bohr proposed a theory for the hydrogen atom based on quantum theory that energy is transferred only in certain well defined quantities. -
Sir James Chadwick
Chadwick interpreted this radiation as being composed of particles with a neutral electrical charge and the approximate mass of a proton. This particle became known as the neutron
