1. Early Ideas About Atoms

2. Democritus Greek Philosopher who lived about 440 B.C.
He thought you could “cut” down matter into pieces, until you reached the smallest possible piece
He named these pieces atoms which is Greek for “uncuttable”

3. John Dalton A British school teacher
In 1802 proposed an Atomic Theory.
He carried out experiments and concluded that atoms have different characteristics.
To this day, scientists have found few exceptions to his theories.

4. Atomic Theory Atoms can’t be broken into smaller pieces
Atoms of the same element are exactly the same
Atoms of different elements are different

5. Ex. Water- H2O 2 Hydrogen 1 Oxygen
4. Atoms of two or more elements can combine to form compounds
5. Atoms of each element have unique mass
6. The masses of the elements in a compound are always in constant ratio
Ex. Water- H2O
2 Hydrogen
1 Oxygen