| Democritus | -greek philosopher
-first to postulate about matter
-believed matter was made of “atomos”, indivisible particles. |
| Aristotle | -greek philosopher
-thought matter as belonging to four categories: earth, water, wind, fire
-accepted explanation for 1500 years |
| Galileo Galilei | -"father of modern science"
-first to incorporate mathematics into laws of nature
-first to go beyond philosophy and conduct proper scientific experiments. |
| John Dalton | -law of constant proportions: dalton realized that all elements combine in constant proportions to form new substances.
-billiard ball model: atoms are build similar to billiard balls. they are small, invisible particles.
-first to make an atomic theory:
1. all matter is made of atoms
2. atoms of the same element are identical in every way
3. atoms of different elements are different
4. atoms are held together by an invisible force |
| Mendeleev | -first person to create an orderly arrangement of
the 63 known elements
-elements were arranged from heaviest to lightest (mass) |
| Rutherford | -in 1899, rutherford bombarded thin sheets of gold foil with alpha particles.
-most particles passed through the foil without being deflected.
-some particles, though, bounced right back as if they had hit a solid object.
-conclusions:
1. atoms have a nucleus with a positive charge
2. atoms are mostly empty space
3. electrons float in this space |
| Thomson | -used a cathode ray tube and a magnetic field to determine the ratio of charge to mass (e/m) of an electron.
-found electrons to be much smaller than the smallest atom (hydrogen) and that the same particles were being emitted from every type of material he used in his experiment.
-concluded:
1. atoms were not indivisible
2. instead, atoms of every kind contained the same type of small negatively charged particles called electrons.
3. for atoms to be neutrally charged, their electrons must float in a positively charged substance.
-developed plum-pudding model |
| Moseley | -did experiments which concluded:
1. elements have more protons the heavier they are
2. the atomic number was the number of protons in the element’s nucleus
-began rearranging the periodic table according to the atomic number |
