1. Oxidation and Reduction

Loss of Electrons

Oxidation

Gain of Electrons

Reduction

Other ways to identify Oxidation/Reduction

• loss/gain of Oxygen

• loss/gain of Hydrogen

• Change in Oxidation State

Redox Reaction

Any reaction that involves the transfer of electrons from one entity to another

What must be remembered about Redox Reactions?

the # of electrons lost by one element, has to be the same number gained by the other element

Tell me about Oxidation Numbers

• apparent charge that an atom would have in a molecule/ion if electron pairs in covalent beds are treated as ionic (e⁻ go to move EN atom)

• doesn’t usually represent actual charge

• can be +ve or -ve

• charge represents the # of electrons gained/lost

What is the first rule of assigning Oxidation States?

In simple ions, OS = as charge found on the periodic table

What is the second rule of assigning Oxidation States?

free/uncombined elements have an OS of 0

What is the third rule of assigning Oxidation States?

Neutral compounds have an OS of 0

• e.g. MgO: +2 +(-2) = 0

What is the fourth rule of assigning Oxidation States?

Polyatomic ions’ OS = their charges

• e.g. In SO₄²⁻, the sum of OS = -2

What is the fifth rule of assigning Oxidation States?

The usual OS for an element is the same as the charge on its most common ion

• e.g. H in H₂O is +1

What is the sixth rule of assigning Oxidation States?

elements that are:

• most non-metals

• bottom of group 14

• transition metals

have oxidation states that vary in different compounds*

Elements with a charge of +1

Li, Na, K

Elements with a charge of +2

Mg, Ca

Elements with a charge of -1

1. F because it is the most electronegative element

2. Cl, except when it is combined with O or F, since it is less electronegative

Elements with a charge of -2

O, except in peroxides like H₂O₂ where it is -1 and OF₂ where it is +2

Hydrogen

+1, except in metal hydrides like NaH, where it is -1

• H is more electronegative and therefore has a stronger electron control

Steps to figure out Oxidation State

1. Write the oxidation numbers you know

2. Solve for the unknown oxidation number

How would you determine if a reaction is a redox reaction?

Any change in oxidation state during a reaction is an indication that redox processes are occurring

How do you know which species are going to be oxidized/reduced?

increase in oxidation number represents oxidation, and a decrease represents reduction

Tell me about naming compounds via OS

• when elements can have different OSes, their name can change depending on their state

• OS are notates by -/+ and a # (-2)

• Oxidation Numbers are placed after an element/compound in Roman numerals and are numerically equivalent to OS (e.g. Cu (II)