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415 BCE
Democritus
Democritus was a Greek philosopher who proposed the idea that matter is made of tiny. Democritus discovered that atoms are small hard particles. Also that atoms are always moving. He also discovered that atoms from different materials by joining together. -
John Dalton's Atomic Theory.
John Dalton was an English chemist. John Dalton discovered:
1 The nature of atoms.
2 Everything is made up of atoms.
3 All atoms of some elements are identical.
4 Compounds are made up of different atoms. -
J.J. Thomson Ray Tube
J.J. Thomson was an English scientist.
He discovered the electron in a series of experiments designed to study the nature of electric discharge in a high-vacuum cathode-ray tube, an area being investigated by numerous scientists at the time. -
Lord Ernest Rutherford.
Lord Ernest Rutherford was anew Zealand physicist.
He discovered a famous experiment called the gold foil experiment. He used a thin sheet of gold foil. He also used special equipment to shoot alpha particles (positively charged particles) at the gold foil. The experiment showed that atoms are made of a small positive nucleus; positive nucleus repels (pushes away) positive alpha particles.
Atoms are mostly empty space. -
Niels Bohr's Atom Model
Niel Bohr was a Danish Physicist. He proposed a model of the atom that is similar to the model of the solar system. He discovered that electrons are negatively charged and protons are positively charged.
