Atomic Structure

Empedocles

490 BCE

Suggested there were only four basics seeds: earth, air, fire, and water.

Aristotle

348 BCE

Added the idea of "qualities", heat, cold, dryness, moisture, as bacin elements which combinated as shown in the diagram.

Dalton

1803

1.All matter is composed of extremely small particles. Dalton,like Democritus,called these particle “atoms”.
2.Atoms of a given element are identical in size,mass,and other properties.
Atoms of different elements differ in size,mass,and other properties.
3. Atoms cannot be subdivided,created,or destroyed.
4.Atoms of different elements can combine in simple whole number ratios to form chemical compounds.
5.In chemical reactions,atoms are combined,separated,or rearraged.

J.J Thompson

1897

J.J Thompson was an English scientist. He discovered the electron when he was experimenting with gas discharge tubes. He noticed a movement in a tube. He called the movement cathode rays. The rays moved from the negative end of the tube to the positive end. He relized thet the rays were made of negatively charged particles electrons.

Lord Ernest Rutherford

1911

Ernest Rutherford conducted 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. Most particles passes straight throug the foil like the foil was not there. Some particles went straight back or were deflected (went in another direction) as if they had hit something.

Niels Bohr

1913

Niels Bohr was a Danish physicist. He proposed a model of the atom that is similar to the model of the solar system. The electrons go around the nucleus like planets orbit around the sun. Al electrons have their energy levels, a certain distance from the nucleus. Each energy level can hold a certain number of electrons. Level 1 can hold 2 electrons. Level 2, 8 electrons. Level 3, 18 electrons. Level 4, 32 electrons.
The energy of electrons goes up from level 1 to other levels.