Oxidation numbersOxidation numbers

Oxidation numbersOxidation numbers Oxidation numbers are used to Oxidation numbers are used to

describe the distribution of describe the distribution of electrons among bonded atoms.electrons among bonded atoms.

Covalent bonds involve sharing of Covalent bonds involve sharing of electrons, but oxidation numbers electrons, but oxidation numbers show what the distribution would be show what the distribution would be if the electrons were completely if the electrons were completely transferred.transferred.

Guidelines for Assigning Oxidation Numbers Guidelines for Assigning Oxidation Numbers ( see p. 180 for a complete list)( see p. 180 for a complete list)

The oxidation of any free (uncombined) element The oxidation of any free (uncombined) element is zero.is zero.

The oxidation number of a monatomic ion is The oxidation number of a monatomic ion is equal to the charge of the ion.equal to the charge of the ion.• e.g.e.g. The oxidation number of KThe oxidation number of K++ is +1. is +1.

The oxidation number of each hydrogen atom is The oxidation number of each hydrogen atom is +1, unless it is combined with a metal, then it has +1, unless it is combined with a metal, then it has a state of -1.a state of -1.

The oxidation number of fluorine is always -1.The oxidation number of fluorine is always -1. The oxidation number of each oxygen atom in The oxidation number of each oxygen atom in

most of its compounds is -2.most of its compounds is -2.

Guidelines for Assigning Oxidation Numbers Guidelines for Assigning Oxidation Numbers ( see p. 180 for a complete list)( see p. 180 for a complete list)

The algebraic sum of the oxidation The algebraic sum of the oxidation numbers for all the atoms in a numbers for all the atoms in a compound is zero.compound is zero.

The algebraic sum of the oxidation The algebraic sum of the oxidation numbers for all the atoms in a numbers for all the atoms in a polyatomic ion is equal to the charge polyatomic ion is equal to the charge on that ion.on that ion.

Example: Determine the oxidation numbers Example: Determine the oxidation numbers for each atom in KMnOfor each atom in KMnO44

This compound is made up of a KThis compound is made up of a K++ cation and an cation and an MnOMnO44

-- anion. anion. The KThe K++ is a monatomic ion with a charge of +1, so is a monatomic ion with a charge of +1, so

its oxidation number is +1.its oxidation number is +1. Assume that each O atom has an oxidation Assume that each O atom has an oxidation

number of -2.number of -2. The MnOThe MnO44

-- has a total charge of -1. There are 4 O has a total charge of -1. There are 4 O atoms, each with an oxidation number of -2atoms, each with an oxidation number of -2

The oxidation number of the Mn may be found by The oxidation number of the Mn may be found by the equation:the equation:• Mn + 4(-2) = -1Mn + 4(-2) = -1

Therefore, the oxidation number of Mn in this Therefore, the oxidation number of Mn in this compound is +7.compound is +7.

Example: Determine the oxidation numbers Example: Determine the oxidation numbers for each atom in Co(NOfor each atom in Co(NO22))22

The anion is the nitrite ion, NOThe anion is the nitrite ion, NO22--..

Assume that each O atom in the nitrite ion has an Assume that each O atom in the nitrite ion has an oxidation number of -2.oxidation number of -2.

The NOThe NO22-- has a total charge of -1. There are 2 O has a total charge of -1. There are 2 O

atoms, each with an oxidation number of -2atoms, each with an oxidation number of -2 The oxidation number of the N may be found by The oxidation number of the N may be found by

the equation:the equation:• N + 2(-2) = -1N + 2(-2) = -1

Therefore, the oxidation number of N in this Therefore, the oxidation number of N in this compound is +3.compound is +3.

Since there are two nitrate ions, each with a Since there are two nitrate ions, each with a charge of -1, the charge on the Co must be +2. charge of -1, the charge on the Co must be +2. As an ion, its oxidation number is equal to its As an ion, its oxidation number is equal to its charge.charge.