att - Timeline

DEMOCRITUS Named smallest piece of matter " Atomos " meaning " not to be cut " They were small, hard particles that were all made of the same material but different shapes and sizes All atoms were infinite in number. always moving and cable of joining together

JAMES CHADWICK His neutrons have no electrical charge His neutrons have a mass nearly equal to the mass of a proton The unit of measurement for subatomic particles is the the " atomic mass unit " ( amu )

JOHN DALTON Matter consists of small particles called atoms All elements are made up of atoms

ERNEST RUTHERFORD The atom is composed of mostly empty space The atom is small, dense, positively charged nucleus containing most of the atoms mass

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