Models

Often used for things too small or large to be observed, or too difficult to be understood easily

In the case of atoms, scientists use large models to explain something that is very small

History of the Atom

Democritus (400BC) suggested the material world was made up of tiny, invisible particles

• Atomos, Greek for ‘uncuttable’

Aristotle believed that all matter was made up of 4 elements, combined in different proportions

• Fire, Water, Earth, Air

The ‘atomic’ view of matter faded for centuries until early scientists attempted to explain the properties of gases

Re-emergence of Atomic Theory

John Dalton postulated that:

1. All matter is comprised of extremely small, indivisible particles called atoms
2. All atoms of a given element are identical; the atoms are of different elements are different
3. Atoms are neither created nor destroyed in chemical reactions, only rearranged
4. Compounds are formed when atoms of more than one element combine
5. A given compound always has the same relative number and kind of atoms

Voice Notes:

• No need to know dates!
• Reviewed matter
  • Includes all things we can observe with our 5 senses
  • Does not include energy
• Matter is made up of atoms
• Philosophers observed stuff, but never experimented
• John Dalton proved Aristotle was wrong and that Democritus was right
• Although, Dalton didn’t know about Isotopes