2.4 Names and Formulae of Inorganic Compounds

• Binary Ionic Compounds

• Multivalent Ions

• Polyatomic Ions

• Binary Molecular Compounds

• Hydrates

• Acids

Binary Ionic Compounds

The name of any ionic compound is simply the name of its constituent metal ion followed by the name of its constituent non-metal ion.

All compounds are neutral. Ions always associate together in a ratio that results in their charges cancelling to form neutral compounds.

e.g. 2Al3+ + 3S2- → Al2S3

6+ + 6− = 0

text pages 96-97

2.4 Names and Formulae of Inorganic Compounds

Multivalent Ions

Multivalent elements have more than one form of stable ion.

e.g. Fe2+ is the iron(II) ion

Fe3+ is the iron(III) ion

text pages 97-98

so Iron(II) chloride is FeCl2

Iron(III) chloride is FeCl3

2.4 Names and Formulae of Inorganic Compounds

Polyatomic IonsA polyatomic ion is a charged group of covalently bonded atoms.

e.g. NO3- is the nitrate ion

SO42- is the sulphate ion

text pages 98-100

so Calcium nitrate is Ca(NO3)2

Calcium sulphate is CaSO4

2.4 Names and Formulae of Inorganic Compounds

The name of a molecular compound uses a prefix code that provides its formula.

The prefixes used are:

1. mono- 4. tetra- 7. hepta- 10. deca-2. di- 5. penta- 8. octa-3. tri- 6. hexa- 9. nona-

text pages 100-101

Binary Molecular Compounds

e.g. Carbon dioxide is CO2

2.4 Names and Formulae of Inorganic Compounds

Hydrates are salts that have incorporated water molecules in a fixed ratio and pattern into their ionic crystal lattice.

The same prefixes used for naming molecules precede the term –hydrate to provide the ratio of water molecules to ions in the crystal:

1. mono- 4. tetra- 7. hepta- 10. deca-2. di- 5. penta- 8. octa-3. tri- 6. hexa- 9. nona-

text pages 101-102

Hydrates

e.g. Cobalt chloride hexahydrate is CoCl2 ∙ 6H2O

2.4 Names and Formulae of Inorganic Compounds

Anhydrous salts do not have water incorporated into their crystal structure, i.e. they are not hydrates.

Some anhydrous salts are hygroscopic which means they can absorb water from the air to form hydrates.

text page 101

Hydrates

Hygroscopic salts that are being used to keep the air dry in a container (a desiccator) are called desiccants.

2.4 Names and Formulae of Inorganic Compounds

Acids are a special type of molecular compound that can be induced to form hydrogen ions and one type of anion.

The names of acids are based on the name of the anion formed.

text pages 102-103

Acids

If the anion doesn’t contain oxygen then the prefix hydro- precedes the name of the anion and the suffix –ic replaces the –ide in the anion’s name, e.g. hydrogen chloride (HCl) is hydrochloric acid.

If the anion does contain oxygen then the suffix -ic replaces the –ate in the anion’s name or the suffix -ous replaces the –ite in the anion’s name , e.g. hydrogen nitrate (HNO3) is nitric acid and hydrogen nitrite (HNO2) is nitrous acid.

2.4 Names and Formulae of Inorganic Compounds