The Names and Formulae of Compounds

Names: To name an ionic compound, you just put the names of the ions together, with the positive one first.

Ions in compound Name K+ and F- Potassium fluoride Ca2+ and S2- Calcium sulfide

Formulae: 1) Write down the name of the ionic compound. 2) Write down the symbols for its ions. 3) The compound must have no overall charge, so balance the ions until the positive and negative charges add up to zero. 4) Write down the formula without the charges.

Examples:

1) Lithium fluoride 2) The ions are Li + and F- 3) One Li + is needed for every F-, to make the total charge zero. 4) The formula is LiF.

1) Sodium sulfide 2) The ions are Na+ and S2- 3) Two Na+ ions are needed for every S2- ion, to make the total charge zero. Na+, Na+, S2-. 4) The formula is Na2S.

Other ions: Silver forms only Ag+ ions Zinc forms only Zn2+ ions. Some transition metals can form more than one ion. For example, copper and iron.

Ion Name Compound + Cu Copper(I) Copper(I) oxide (Cu2O) Cu2+ Copper(II) Copper(II) oxide (CuO)

2+ Fe Iron(II) Iron(II) chloride (FeCl2) 3+ Fe Iron(III) Iron(III) chloride (FeCl3) Compound Ions: Some ions can be formed by combining more than one atom together. These are called compound ions. Remember though, each is just one ion, even though it contains more than one atom. Examples:

+ NH4 Ammonium ion

2- SO4 Sulfate ion

2_ CO3 Carbonate ion

- NO3 Nitrate ion

OH- Hydroxide ion

Is it –ide or is it –ate?

1) When a metal combines with another element, to form a compound, its name does not change. 2) The element it is combining with changes its name by adding –ide to the end. e.g. Calcium + Chlorine  Calcium chloride

Magnesium + Oxygen  Magnesium oxide

EXCEPT, When a metal element combines with another element that has oxygen combined to it already, e.g.

Carbonate CO3 Nitrate NO3 Phosphate PO4 Sulfate SO4

The number tells how many oxygen atoms are attached. The suffixes to all of the names should now all end in –ate. For example,

Copper sulfate CuSO4 Calcium carbonate CaCO3 There are two other groups. They are the hydroxide and ammonium groups.

1) The hydroxide group has one oxygen atom attached to one atom of hydrogen, OH. e.g. Sodium hydroxide NaOH Potassium hydroxide KOH

3) The ammonium group has one atom of nitrogen attached to four atoms

of hydrogen, NH4. e.g. ammonium chloride NH4Cl