1. The Atom Democritus-teacher & philosopher (400BC) Hypothesized : smallest unit of matter is atom (Greek “atomos” – indestructable)

2. Opposed by: Aristotle-matter made of natural material called byle Plato & the Church No experimental evidence to support Democritus

3. John Dalton Early 1880’s Proposed first Atomic Theory Had experimental support How atoms combine to form compounds Ratios of elements combined to form compounds

4. Dalton’s Atomic Theory 1.All elements are composed of indivisible particles called atoms.

5. 2. Atoms of the same element are identical. Atoms of one element are different than atoms of another element.

6. 3. Atoms of different elements can physically mix together or chemically combine in simple whole number ratios to form compounds.

7. 4. Chemical reactions occur when atoms are separated, joined or combined. Atoms of one element are NEVER changed into atoms of another element during a chemical reaction.

8. Atom The smallest particle of an element that retains the properties of that element.

9. Atoms are VERY small One penny contains 2.4 x 10 22 atoms 6 x 10 9 people on earth 1 x 10 8 copper atoms lined up = 1 cm Can be seen with a Scanning Tunneling Electron Microscope Atoms can be manipulated, so Future- make atom sized circuits and computer chips