Oxidation State Rules

Oxidation State Rules
Pure elements are all zero.
Fluorine is -1.
Metals: 1A are +1, 2A are +2, and aluminum is +3.
H is usually +1 (when in a compound with a non-metal), is –1 when in a compound with a less electronegative metal (hydride).
Oxygen is usually –2.
Group 7A elements (halogens) are -1.

Ionic and covalent bonds

Ionic bonds are non-directional. Covalent bonds are directional. Ionic bonds don't form discrete molecules. The atoms in covalent bonds share electrons.

Covalent bonds form between nonmetals. When a metal bonds with a nonmetal, that bond is an ionic bond.

If there is a huge electronegativity difference between two atoms, the higher electronegative atom takes the electron, doesn't share.

A non-polar bond is a covalent bond where the electronegativity difference between the atoms is zero or nearly zero.

A polar bond is a covalent bond where the electronegativity difference between the atoms is greater than 0.4.

How to find number of neutrons

How many neutrons does an atom have?
Atomic mass of the atom - atomic# of the atom.
Examples:
Neutrons of Zn = 65 - 30 = 35.
Neutrons of O^2- = 16 - 8 = 8.
Neutrons of Y³⁺ = 89 - 39 = 50.

Ions and isotopes definitions

Ions are atoms in which the number of electrons does not equal the number of protons.

Isotopes are atoms that differ in the number of neutrons.

Ions are atoms that have a charge.

The charge of an ion is the number of protons minus the number of electrons:
Ion charge = #protons - #electrons.