1. The Early Discoveries that led to the Atomic Theory

2.  J.J. Thompson used the Cathode Ray to determine the mass/charge ratio of an electron.  He discovered that atoms were divisible into smaller parts.

3.  Used this to discover the charge of an electron

4.  JJ Thompson came up with a theory that electrons are embedded into a positively charged sphere

5.  Rutherford’s experiment showed him that something dense and positively charged was in an atom

6. Atomic Theory Today

7.  Atom is electrically neutral  Composed of a positively charged central nucleus surrounded by one or more electrons

8.  A is the mass number (protons plus neutrons)  Z is the atomic number (protons)  X is the atomic symbol  An isoptope has the same number of protons but a different number of neutrons A Z X

9.  Atomic Mass Unit is 1/12 of carbon atom (1.008 amu for a hydrogen atom)  Mass spectrometry is used to determine the atomic mass of an element  First divide the element’s mass number by 12 to get the atomic mass unit  Then multiply your answer by the percent abundance of the element to get the amu for that isotope  After you do this for all the isoptopes, you must add all of the amu’s together and you will get your atomic mass

10.  All matter is composed of atoms  Atoms can not change into other atoms in a reaction  All atoms have the same number of protons and electrons which determines the behavior of the element  Compounds are formed by a combination of two or more elements in specific ratios.