Page 16 - Curriculum Visions Dynamic Book

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2: States of water
Many compounds can be a solid, a liquid, or a gas. Each of these forms is called a state of matter.
We call the liquid form of water simply “water” because that is how it normally appears to us. The other states of water are as a gas – called water vapour (see pages 19 and 20) – and as a solid – called ice. Water can also take part in many chemical reactions, that is, it is a reactive substance.
steam, which is water vapour at the boiling point of water, is a particularly reactive substance; liquid water is still quite reactive, but ice is inert and unreactive.
The change from steam to water leads to condensation and a reduction in volume; the change from water to ice, solidification, leads to an expansion in volume. We will see more of this below.
Water (a molecule of hydrogen and oxygen atoms) may be reactive, but it is also a stable substance and will not dissociate into hydrogen and oxygen gases unless a
See Vol. 9: Air for more on water vapour.
Gases
Weak forces between particles mean that they move around with no order.
large amount of energy is applied, for example, in the form of an electric current (see pages 55
and 56). Thus, heating water
to its boiling point will not make it dissociate; it merely makes it vaporise.
As we have seen,
water can form a gas, a liquid, and a solid. But
not all substances are
like this. That is partly because water consists of two atoms (hydrogen and oxygen), while some liquids
(Right) The attractive forces between particles are different for each state.
Liquids
The forces between particles in a liquid are intermediate between gases and solids and lead to a loose, irregular arrangement.
Solids
Strong forces between particles in a solid
give a closely packed and regular structure. There is little space between particles.
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