SL Chem - Unit #1: Oxidation Number Rules

Oxidation

is a reaction where the element has a loss of electrons

Reduction

Is a reaction where the element gains electrons

Redox reactions

A reaction where both oxidation and reduction occurs in one equation

When writing their oxidation number…

It’s written as a superscript with the positive/negative charge before the #

• If the sign is after the number that represents a charge

Oxidizing Agent

The part of the equation that “do” the oxidizing

• they are electron donors that lose their own electrons and give it to another element

Reducing Agent

Another substance that caused the reduction of the former element

• Electron acceptors that take electrons from other elements

Oxidizing states (numbers)

given to atoms in a compound to show how much control the atom has over the electrons in the compounds

When an element gains electron….

They lose control over the compound

• higher # of electrons gains = lose even more control

When an element loses electrons…

It gains control over the compound

Oxidation Number Rule 1

The oxidation number for any atom in an element in its natural state at room temperature is zero

Oxidation Number Rule 2

The oxidation number of a mono-atomic ion is equal to the charge on the ion

Oxidation Number Rule 3

The oxidation number of hydrogen atoms in most of its compounds is +1, except METAL hydrides (which are -1)

Hydride

Any chemical compound where hydrogen is combined with another element

• Metal hydrides: Hydrogen combined with a metal

Oxidation Number Rule 4

The oxidation number of each oxygen atom in most of its compounds is -2.

• Peroxide: H₂O₂ = -1

• OF₂ = 2

Oxidation Number Rule 5

In compounds, the elements of group 1, group 2, and aluminum have positive oxidation numbers of +1, +2, and +3, respectively

• In ionic compounds the oxidation number is equal to it’s charge

Oxidation Number Rule 6

The sum of the oxidation numbers of all the atoms must equal the apparent charge of that particle

• Eg, (SO₄)^2- is written as SO₄ = -2

Oxidation Number Rule 7

When there is a molecular compound without hydrogen or oxygen, the element with a higher electronegativity is assigned the oxidation number equal to the charge it usually has when it is in ionic compounds.

Oxidation Number Rule 8

The sum of the oxidation numbers of all the atoms in a polyatomic ion equals the charge on the ion