1.  Atomic Theories  A timeline…

2. or as you may prefer to remember it…

3. I believe atoms are the smallest pieces of matter.

4.  He came up with the term “atom”  He thought atoms had different shapes and sizes  He thought they were indivisible and indestructible  “atomists” – people who followed his beliefs

5.  His beliefs were more like the early Greeks  Philosopher Atoms? Give me a break! I could speak for hours against their existence.

6.  Dalton’s Atomic Theory  Matter is composed of atoms  All atoms of the same element are identical; different elements have unique atoms  They cannot be destroyed or created  They combine to form compounds

7.  Discovered the electron  Proved the atom can be divided  Plum pudding model

8.  Atoms have a dense “nucleus”  Discovered the proton

9.  Discovered the neutron

11.  The number of protons in an atom  Usually the number of electrons also

12.  The number of protons and neutrons  The “rounded” number  Neutrons = mass number – atomic number  Isotopes – atoms possessing the same number of protons but different neutrons

13.  The “unrounded” number  It’s an average “mass” of all the atoms of an element in nature