
1. Many
atoms, especially when heated together, combine with each other to form a
.
2. The new substance formed will have its own chemical
in words and the ratio of the atoms combined can be shown as a chemical
.
3. In general, the chemical change from
to
can be shown as a
equation or as a symbol
.
4. sodium + chlorine ==>
5. copper +
==> copper sulphide
6. magnesium +
==> magnesium oxide
7. iron + sulphur ==> iron
8. magnesium + oxygen ==>

9. Sulphuric acid as the formula H
2SO
4. This means each molecule contains
atom(s) of hydrogen,
atom(s) of sulphur and
atom(s) of oxygen and there are a total of
atoms in the molecule.
10. The formula for an iron oxide is Fe
2O
3. This means
oxygen atoms are combined with 2
atoms and a total of
atoms in the formula.
11. The molecule in the picture above on the left is made up of
atoms and
different elements.