Compounds

Objectives
• Know how to name compounds

• Know how to write formulas

• Know how to work out how many of each
atom there are in a compound, based on
a formula

Atoms in compounds
Compounds contain two or more
different types of atom.
The compound, water,
exists as molecules.
Each water molecule
consists of two
hydrogen atoms
joined to one oxygen
atom.

Making a compound – water
Water is produced from the chemical reaction between
hydrogen and oxygen.

hydrogen + oxygen water

H H
+ O O
H H
Two hydrogen molecules react with one oxygen
molecule to produce two molecules of water.
Why does water have different properties to its
elements?

Properties of a compound –
carbon dioxide
A compound has different properties to the elements
from which it is made because the atoms are joined
differently.
carbon + oxygen carbon dioxide

+
Black solid Colourless gas in Colourless gas used
used as fuel. which many in fizzy drinks and
substances fire extinguishers.
burn.

C + O O

Copper Element Mercury Element

Aluminium Element Oxygen Element

Water (H2O)

Carbon dioxide (CO2)

Iron sulphide (FeS)

Naming simple compounds
To name simple compounds of metals and non-metals:

1. Write down the name of the metal.
2. Write down the name of the non-metal,
changing the ending of the word to “-ide”.

What is the name of the compound made when the
following elements combine?

 magnesium and oxygen magnesium oxide

 sodium and chlorine sodium chloride

 oxygen and iron iron oxide

Naming simple compounds
What is the name of each compound formed by these
metal and non-metal elements?
Element 1 Element2 Name of compound
iron sulphur iron sulphide
magnesium nitrogen magnesium nitride
sodium chlorine sodium chloride
tin oxygen tin oxide
aluminium bromine aluminium bromide
nickel iodine nickel iodide
zinc sulphur zinc sulphide
lithium nitrogen lithium nitride

Naming further compounds
Many compounds contain more than two elements.
For compounds containing two elements plus oxygen,
the ending of the other non-metal usually changes to “ -
ate”.
Element 1 Element 2 Element 3 Name of compound
nickel sulphur oxygen nickel sulphate
magnesium nitrogen oxygen magnesium nitrate
sodium nitrogen oxygen sodium nitrate
copper sulphur oxygen copper sulphate
aluminium bromine oxygen aluminium bromate

Composition of compounds
A compound contains atoms from different elements
that are chemically joined together.
A compound always contains a particular amount of
each element. It has a fixed composition.

Compound names can get quite long and complicated,
so the symbols of the elements are used as a
shorthand.
The symbols of the elements in a compound are
combined to give the formula of the compound.

What is the formula of
carbon dioxide?

Writing a formula
A formula uses the symbols of the elements in a
compound.
When there is more than one atom of each element, the
number is always written after the symbol.

carbon dioxide
carbon atom = 1
oxygen atoms = 2
formula = CO2

water
hydrogen atoms = 2
oxygen atom = 1
formula = H2O

The formula shows the ratio of atoms in a compound.

What is the formula?
What is the formula of each of these compounds?
(In a formula put the metal first as when naming a compound.)

1. Titanium oxide
For every titanium atom there are two oxygen atoms.
Formula = TiO
2

2. Lithium oxide
For every two lithium atoms there is one oxygen atom.
Formula = Li O
2

3. Aluminium chloride
For every aluminium atom there are three chlorine atoms
Formula = AlCl
3

What is the formula?
What is the formula of each of these compounds?
(In a formula put the metal first as when naming a compound.)

1. Silicon chloride
For every silicon atom there are four chlorine atoms.
Formula = SiCl
4

2. Manganese oxide
For every manganese atom there are two oxygen atoms.
Formula = MnO
2
3. Aluminium oxide
For every two aluminium atoms there are three oxygen atoms.
Formula = Al O
2 3

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