1. Electron and Energy Level Notes
Electrons have a negative charge
Electrons travel around the nucleus in a region called the electron cloud.
It is impossible to determine the exact location of an electron within the cloud at any particular moment.

2. In a Bohr model of the atom, electrons are shown orbiting the nucleus in set paths called energy levels. Generally the following rules can be used to make a Bohr model for the 1st 18 elements:
Nucleus

3. The 1st energy level (Level K) can hold no more than 2 electrons.
The 2nd energy level (Level L) can hold no more than 8 electrons.
The 3rd energy level (Level M) can hold no more than 8 electrons
Lower energy levels must be filled before going to higher levels.

4. The number of electrons in the outer most energy level.
Valence Electrons
The number of electrons in the outer most energy level.
Determines chemical properties such as reactivity.

5. Hydrogen
Helium
Oxygen
Sodium H 1 1 1 1 1
P=1
N=0