1. OHHHHH YEAHHHHH

2.  400 BC Greece-philosophers  Democritus said that there must be something that cannot be divided  He called this particle atomos  Aristotle claimed that no such particle exists  Neither did any experiments to test their claim  They were just thinkers

3.  Definition: An atom is the smallest particle into which an element can be divided and still be that element.  Considered the basic unit of matter even though it is made up of certain other particles

4.  John Dalton-1808  Used experimental evidence to make a few major conclusions  All mater is made up of atoms  All atoms of a certain element are identical  Every substance is made up of atoms combined in certain ways

5.  JJ Thomson-1897  Used evidence to explain that there a particles of negative charge mixed through Dalton’s original sphere  Ernest Rutherford-1909  Discovered a nucleus (tiny dense positive center)  Positively charged particles called protons  The atom is mostly empty space

6.  Niels Bohr - 1913  Electrons move in circular paths around the nucleus  Each path is a certain distance from the nucleus and has a certain amount of energy associated with it  James Chadwick- 1932  Discovered the nucleus had uncharged particles called neutrons

7.  Erwin Schrodinger  Electrons move around the nucleus not in circular orbits but instead in areas called the electron cloud

8.  Protons  Positively charged particles (1+)  It has a mass of 1.7 x 10 -24 grams  This is equal to a mass of 1 amu or u  Neutrons  No electrical charge (neutral)  Slightly larger than protons but about 1 amu

9.  Negatively charged particles (1-) located outside the nucleus  So small they are about 0 amu  It is not possible to find their exact positions and speed at the same time (this is why we call it a cloud)  The number of electrons in an atom equals the number of protons giving it a net charge of 0  When an atom gains or loses electrons we call the atom an ion

10.  Atomic number  The number of protons in an atom  Mass Number  The total number of protons in neutrons in an atom  Atoms can have different number of neutrons so we use calculations to find an average mass number