Rules for Determining Oxidation Numbers

Rules for Determining Oxidation Numbers

The oxidation number of a single uncombined atom or diatomic molecule is zero.

The oxidation number of a monatomic ion is equal to the charge on the ion.

In most cases: H = +1 (exception: hydride ion: -1)

In most cases: O = -2 (exception: peroxide ion: -1; also in some rare binary molecular compounds like oxygen difluoride: +2)

In binary molecular compounds, the more electronegative ion gets the negative charge.

The sum of the oxidation numbers in a compound equals the overall charge.

H

2.2

Electronegativities

Li

0.9

Be

1.5

B

2.0

C

2.6

N

3.1

O

3.5

F

4.0

Na

0.9

Mg

1.2

Al

1.5

Si

1.9

P

2.2

S

2.6

Cl

3.2

K

0.8

Ca

1.0

Ga

1.6

Ge

1.9

As

2.0

Se

2.5

Br

2.9

Rb

0.8

Sr

1.0

In

1.7

Sn

1.8

Sb

2.1

Te

2.3

I

2.7

Cs

0.7

Ba

0.9

Tl

1.8

Pb

1.8

Bi

1.9

Po

2.0

At

2.2

Fr

0.7

Ra

0.9