Ions Atoms are neutral, the number of positive protons is balanced by the number of negative electrons. Ions are atoms that have become charged. There are two sorts of ions; a)Positive b)Negative

Positive ions If an atom loses an electron(s), the ion formed with have a positive charge. M → M + + e Positive ions are called cations. Think of the T as a + if you get confused! Cations are generally formed by metals.

Ions with a charge of +1 include; Hydrogen ions, aka protons H +. Ions of group 1 elements, eg; Lithium, Li +. Sodium, Na +. Potassium, K +.

Ions with a charge of +2 include; All ions of group 2 elements eg; Mg 2+ Ca 2+ Ba 2+ Other metals such as Fe 2+, Cu 2+ and Zn 2+.

Ions with a charge of +3 There are few +3 ions, as lots of energy are required to form them, they include; Aluminium, Al 3+. Iron, Fe 3+. Chromium, Cr 3+.

Some metals can often form more than one ion eg; Iron forms both Fe 2+ and Fe 3+. Copper usually forms Cu 2+, but can also be Cu +

Negative ions Some atoms accept an electron(s), becoming negatively charged; X + e → X - Negative ions are called anions.. Anions are generally formed by non- metals.

Ions with a charge of -1 include; Hydride ions, H -. Halide ions (Group 7), eg; Floride F - Chloride Cl -, Bromide Br -, Iodide I - Hydroxide ions, OH-. Hydrogen carbonate (aka bicarbonate), HCO 3 - Manganate, MnO 4 - Nitrate,NO 3 -

Ions with a charge of -2 include; Carbonates, CO 3 2-, Sulphates, SO 4 2-, Sulphites, SO 3 2- Dichromate, Cr 2 O 7 2- Chromate, CrO 4 2-.

Ions with a charge of -3 include; Phosphates, PO Nitrides, N 3-, Phosphides, P 3-

Ions with a higher charges. There are few ions with a charge greater than -2, because to form them requires lots of energy. The only common ion with a charge of -3 is the Phosphate, PO The only common ion with a charge of - 4 is the carbide ion, C 4-.

NO 3 - CO SO 4 2- O 2- Construct a table summarising the names and charges of ions.

Using charges to write formulae An ionic compound consists of a cation and an anion. Compounds are neutral. This means that the number of positive charges on one ion must be equal to the number of negative charges on the other. So the charges on ions must be known to be able to write formulae and equations.

Think of ions like pieces of a jicksaw… M 2+ X 2- To make a neutral compound they must “fit”. M 2+ X 2- Compound MX

M 2+ Y-Y- Y-Y- Y-Y- Compound MY 2

Ionic compounds are neutral. The number of positive charges is cancelled out by the number of negative charges, leaving no overall charge. Eg; Lithium chloride Lithium ions have a charge of +1. Chloride ions have a charge of -1. So one lithium ion will be balanced by one chloride ion = 0 Thus the formula of lithium chloride is Li Cl.

Calcium carbonate Calcium ions have a charge of +2 Carbonate ions have a charge of = 0 One calcium ion is combined with one carbonate ion. So the formula of calcium carbonate is CaCO 3. Ca 2+ CO 3 2- Ca 2+ CO 3 2-

Sodium oxide Sodium ions have a charge of +1. Oxide ions have a charge of -2. So the formula of sodium oxide is Na 2 O. Two positive sodium ions are needed to balance one negative oxide ion. 2(+1) + -2 = 0

Barium hydroxide Barium ions have a charge of +2. Hydroxide ions (OH-) have a charge of -1. This means that two hydroxide ions are needed to balance one barium ion (-1) = 0 So the formula of barium hydroxide is Ba(OH) 2 Ba 2+ OH- Ba 2+

Aluminium bromide Aluminium ions have a charge of +3. Bromide ions have a charge of -1. This means that three bromide ions are needed to balance one aluminium ion (-1) = 0 So the formula of aluminium bromide is AlBr 3 Al 3+

Iron (iii) sulphide Iron (iii) ions have a charge of +3. Sulphide ions have a charge of -2. This means that three sulphide ions are needed to balance two iron (iii) ions. 2(+3) + 3(-2) = 0 So the formula of iron (iii) sulphide is Fe 2 S 3

Eg; What is the formula of sodium carbonate? Sodium is a metal, and forms a cation Na+. Carbonate contains non metals, and is an anion; CO 3 2- Two sodium ions are required to neutralise the double charge on the carbonate. Therefore the formula is Na 2 CO 3.