1. Atomic Theory Timeline

2. Democritus Everything made of small particles Called atmos
Earth, air, fire, and water

3. Antoine Lavoisier Law of Conservation of Mass
Mass cannot be created or destroyed
Mass of reactant= mass products

4. Joseph Proust
Law of Constant Composition or Law of Definite Proportions
a chemical compound always contains the same elements in exactly the same proportions by mass.

5. John Dalton Atomic Theory of Matter
Each element is composed of extremely small particles called atoms
All atoms of a given element are identical, but they differ from atoms of other elements
Atoms are neither created nor destroyed in a chemical rxn
A given compound always has the same relative numbers and kinds of atoms

6. J. J. Thompson Led to the Plum- Pudding model of the atom
Atoms are neutral so have both positive and negative charges
Positively charged sphere with negative charges imbedded in it.
Used cathode ray- tube experiments to discover the electron
Small negatively charged particles that are part of every atom

7. Rutherford Discovers the nucleus Gold foil experiment
Nucleus is tiny, dense, and positively charged
Almost all mass is in nucleus
Surrounded by mostly empty space where negatively charged particles are.

8. Atomic structure

9. Parts of Atoms Nucleus- small- holds protons and neutrons
Protons (p+)- positively charged
Nuetrons (n0)- no charge
Mass about equal in size but neutron just bigger
p+ = amu
n0 = amu
Electron cloud- surrounds nucleus holds electrons
Electrons (e-) – negatively charged
Mass = ×10−4 amu
So small add almost no mass to atom

10. Atomic number = # p+
Atoms of a single element always have the same # p+
# p+ = # e-
When atom is neutral
If not neutral, have more or less e-

11. Mass Number
Mass of atom
Number of particles in the nucleus
Mass number = # p+ + # n0

12. Isotopes Atoms of the same element with different masses
Must have different numbers of neutrons
Show which isotope you are talking about using isotopic notation
Lithium-8
83Li

13. Determining # of Particles in Atoms
Name
Symbol
Atomic #
Mass #
# p+
# n0
# e-
Carbon-12 6 7
2411Na 47 22
3416S-2