The Atom

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