1. ELECTRONS Negatively charged particle surrounding the nucleus
Electrons move quickly around the nucleus at a rate of billions of times each second.
In a neutral atom the number of electrons equals the number of protons

2. Location of the electron
Depends on how much energy the electron has
Arranged in energy levels
Lower energy levels are closer to the nucleus

3. Drawing Energy Levels Start with the lowest energy level
Fill energy level completely before placing electrons in the next energy level

4. Energy levels 1st energy level can hold 2 electrons
2nd energy level can hold 8 electrons
3rd energy level can hold 18 electrons
4th energy level can hold 32 electrons

5. Energy Sublevels 1st energy level - S orbital 2 electrons
2nd energy level - S orbital 2 electrons
P orbital 6 electrons
• 3rd energy level S orbital 2 electrons
D orbital 10 electrons
• 4th energy level S orbital 2 electrons
F orbital 14 electrons

6. Electron Shell Structure
The Octet Rule:
In general, atoms are most stable when they have 8 electrons in their outer-most shell. (Octet means 8.) The exception is the first shell which is most stable with TWO electrons. If you know the Atomic Number and Mass Number of an element and the maximum number of electrons in each electron shell you can draw a diagram of the element.

7. Order of Orbital Filling
Electron configuration

8. Electrons and light
When electrons absorb energy they move out to the next energy level
When they lose energy they drop down a level and give off light

9. Colorado - univ of Bolder
Cool site

10. Isotopes
Atoms of the same element that have a different number of neutrons
Round the atomic mass to the nearest whole number to find the number of neutrons in the most common form of the atom
Mass numbers of isotopes differ because the number of neutrons is different