Starter• What are the charges of the ions in these

compounds?▫ NaCl▫ MgF2

▫ CaS▫ Al2O3

▫ HCl▫ HNO3

▫ H2SO4

▫ H3PO4

Starter Answers• What are the charges of the ions in these compounds?

▫ NaCl Na+ Cl-

▫ MgF2 Mg2+ F-

▫ CaS Ca2+ S2-

▫ Al2O3 Al3+ O2-

▫ HCl H+ Cl-

▫ HNO3 H+ NO3-

▫ H2SO4 H+ SO42-

▫ H3PO4 H+ PO43-

• What is different about the second 4 compared to the first 4? (other than the fact they are acids)

Starter Answers• What are the charges of the ions in these compounds?

▫ NaCl Na+ Cl-

▫ MgF2 Mg2+ F-

▫ CaS Ca2+ S2-

▫ Al2O3 Al3+ O2-

▫ HCl H+ Cl-

▫ HNO3 H+ NO3-

▫ H2SO4 H+ SO42-

▫ H3PO4 H+ PO43-

• They only exist as separate ions in solution... We can start to think of atoms in covalently bonded molecules as having their own charges too...

• ...They don’t have charges though...• ... They have oxidation states

Introduction to Oxidation States

ObjectivesBe able to...•Define the terms oxidation state and

oxidation number•Recall the rules for assigning oxidation

numbers•Calculate the oxidation states of specified

atoms in formulae or both molecules and ions.

Specification...Where this comes from...

What do the roman numerals mean???• Iron (II) oxide• Iron (III) oxide• Copper (I) chloride• Copper (II) chloride• Vanadium (III) oxide• Vanadium (IV) carbonate• Vanadium (V) oxide• Potassium dichromate (IV)• Potassium permangenate (VII)

What do the roman numerals mean???• Iron (II) oxide FeO• Iron (III) oxide Fe2O3

• Copper (I) chloride CuCl• Copper (II) chloride CuCl2

• Vanadium (III) oxide V2O3

• Vanadium (IV) carbonate V(CO3)2

• Vanadium (V) oxide V2O5

• Potassium dichromate (IV)K2Cr2O7

• Potassium permangenate (VII)KMnO4

Oxidation Numbers – The Rules!Oxidation numbers always refer to single atoms

The oxidation number of an uncombined element is always 0

O2, H2, NeZn

The oxidation number of Fluorine in a compound is always -1

HF, MgF2, C2F4

The oxidation number of Hydrogen is usually +1 Hydrides are an exception – they are -1

HCl, H2SO4

The oxidation number of Oxygen is usually -2 Peroxides are an exception – they are –1. In OF2 oxygen is a +2

H2O, NO2, etc.

Oxidation numbers of monatomic ions follow the charge of the ion

O2-, Zn2+

The sum of oxidation numbers is zero for a neutral compound. It is the charge on a polyatomic ion

LiMnO4

SO42-

Or put more simply...

Now you try some!•Find the oxidation numbers of in

1. HIO4

2. HIO3

3. HIO4. HI

Answers

•Find the oxidation numbers of in 1. HIO4 H = +1 O = -2 (x4) I =

+72. HIO3 H = +1 O = -2 (x3) I =

+5 3. HIO H = +1 O = -2 (x1) I =

+14. HI H = +1 I = -1

Let’s work out what the roman numerals mean

• Iron (II) oxide FeO• Iron (III) oxide Fe2O3

• Copper (I) chloride CuCl• Copper (II) chloride CuCl2

• Vanadium (III) oxide V2O3

• Vanadium (IV) carbonate V(CO3)2

• Vanadium (V) oxide V2O5

• Potassium dichromate (IV)K2Cr2O7

• Potassium permangenate (VII)KMnO4

More Practice...