Chemistry

1. Chemistry Atomic Theory

2. Democritus The word atom comes from the Greek word atomos, meaning indivisible He also claimed that atoms are always moving and they form different materials by joining together • Proposed that if you keep on cutting an object in half eventually you will have a uncuttable particle. He called this particle the “atom” • Aristotle disagreed with this theory, he felt you could never end up with an indivisible particle, however later he was proved incorrect.

3. John Dalton His theory stated… All substances are made of atoms. Atoms are small particles that cannot be created, divided, or destroyed Atoms of the same element are exactly alike Atoms join with other atoms to make new substances The above theory was not quite correct • British chemist and school teacher • Results of experiments demonstrated that elements combine in specific proportions because they are made of individual atoms.

4. Earnest Rutherford • Student of Thompson • Aimed a beam of positively charged particles at a thin sheet of gold foil. He surrounded the foil with with Zinc Sulfide a substance that glowed when struck by particles. • Rutherford thought that since the atoms were soft blobs (plum putting model) it would shoot straight through. But his data was a little surprising

5. Rutherford’s Results • Some particles shot straight through, while others were deflected. • He presented a new atomic theory (revised Thompson) • He proposed that in the center of the atom is a small dense area which is positively charged called the nucleus. • From his results he calculated that the diameter of the nucleus was 100,000 times smaller that an atom of gold.

6. Niels Bohr • Danish Scientist • Suggested that electrons travel around the nucleus in particular paths. • These path’s are located in certain levels as well as distances. • Electrons can jump levels • Good theory, however still needed to be improved

7. The Modern Theory • Many of the scientists that we discussed contributed to the modern theory in one way, shape or form. Allthough not one scientist perfectly figured it out all helped to reach the modern day theory . • The modern day theory states that we have a nucleus which holds P/N. The electrons are held in shells that (electron cloud) that circle the nucleus of an atom

8. Assignment • Please write a 2 paragraph essay stating the two scientists that you feel are the most important in their contributions to the modern day atomic theory (20 pts)