Chemistry in room 11 > Chapter 9 >
can be categorised as pure materials. They are dull and brittleand they have
very high melting and cooking points. They conduct electricity when they are
melted or in a solution.
Salts are not made up of molecules but ions. Ions are electrically charged atoms.
The best known example sodium-chloride which is the main part of cooking salt.
Sodium-chloride is not made up of sodiumatoms and chlorideatoms but ions.
These ions are, in their solid phase, very regularly organised.
consists of Na+ and Cl- ions that attrackt eachother. The substance is therefore
neutral because the negative charge and the positive charge are the same. So the
ratio of Na+ and Cl- ions is 1:1 so the conclusion must be there are the same
number of positive and negative ions.
This means that the formula should be (Na+)1(Cl-)1 . The index 1 is not noted
and this means that the brackets are not needed. To make it even more easy the
formula Na+Cl- is simplified to NaCl.
are about 100,000 known salts and they all have a high meltingpoint. Stalgmites
and stalagtites in caves are examples of salts. They are mainly made up of a
salt called calcium carbonate or chalk. Other examples of well-known salts are:
plaster stone, copper sulphate, marble, bauxite(alluminium-ore) and rust.
determine the formula for a salt we first need to know the charge of the ions in
the salt. This is easy for NaCl because Na has +1 and Cl has –1. Bur there are
other salts with different charges. Just look at the table.
ions of metals (which always have the same ion-charge) are given the name of the
The ion of potassium (K+) is called the potassium ion.
The name of an ion with more than one ion-charge will get a roman numeral added.
The roman numeral denotes the charge of the ion. In this way Fe2+ is called the
iron(II)ion A negative ion will get the suffix: -ide.
get the formula of a salt there are a number of steps.
the charge of the ion involved.
write down the ions next to
eachother (the metal-ion always in front).
the compound must be
electrically neutral so determine the smallest ratio of ions necessary.
note the ratio-numbers
to the right of the ions.
If the ratio-number is
one, leave it out.
simple ions there arealso complex ions. A complex ion is an electrically charged
particle which consists of more than one atom. You will need to know the
following complex ions:
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Carbonate CO3 2-
Phosphate PO4 3-
Sulphate SO4 2-