I. History(important people and a general idea of what the discovered)
A. 460 BC
~Democritis Develops the IDEA of atoms
B. 1808
~John Dalton came up with the idea that ALL matter is made up of atoms(spheres with perfect elasticity)
C. 1898 and 1804
~J.J. Thompson found that there’s a negative(-) particle called an Electron(e-) ~scattered around a sphere there’s a positive(+) for every (-)
D. 1910
~Earnest Rutherford came up with the experiment to fire Helium Nuclei at Gold foil (only 1 in 10, actually hit and stuck the rest either passed through or bounced off). This suggested the nucleus was in the middle and full of (+) particles
E. 1913
~Niels Bohr said that (e-) were in orbits around the nucleus that held Protons(p+) and Neutrons(-n+)
II. Helium Atom
A. green- Neutrons, Red- Protons, yellow- Electrons, Ring Holding Electrons- Shell

III. Atomic Structure
A. GUIDELINES FOR AN ATOM
~Number of (e-) MUST match number of (p+) [Atomic number represents the number of (p+)/(e-)]
~Shell 1- maximum of 2 (e-), Shell 2- maximum of 8 (e-), Shell 3- maximum of 8 (e-)
B. There are 2 ways to represent the structure of an element or compound
~Electron Configuration
~Dot and Cross Diagram
Particle Charge Mass Location
Neutron (-n+) N/A N/A Nucleus
Proton (p+) Positive (+) 1 Nucleus
Electron (e-) Negative (-) 1 Shell
IV. Dot and Cross Diagram
A. Dot’s and Crosses represents (e-) and circles represent Shells

V. Electron Configuration
A. Represented Numerically by the number of electrons in their shells
B. EXAMPLE:
~7-N- 2,5 ~17-Cl- 2,8,7
~20-Ca- 2,8,8,2 ~14-Si- 2,8,4
~11-Na- 2,8,1 ~5-B- 2,3
~8-O- 2,6
VI. All atomic masses are decimals. They are an average number based upon the relative abundance of their ISOTOPES
VII. An Isotope is the same element but has a different number of neutrons = a different atomic mass.
A. EXAMPLE Nitrogen-7-14 P-7 99.6% Nitrogen-7-15 P-7 0.37%
E-7 E-7
N-7 N-8
99.63/100= .9963 0.37/100= .0037
14(.9963)+15(.0037)=
13.9482+0.0555=
=14.0037
