Page 12 - Curriculum Visions Dynamic Book
P. 12
A compound has a fixed chemical composition. For example, the compound water always has twice as many hydrogen atoms in it as oxygen atoms. So, the formula for water is H2O.A mixture,
on the other hand, contains more
than one substance in no fixed proportion and so cannot be
given a chemical formula.
Unlike mixtures, the elements
that make up a compound are
difficult to separate.
Compounds do not
inherit the properties of the
elements from which they are
made.The properties of the
liquid water (H2O), for example,
are quite unlike the properties of the elements hydrogen and oxygen (both of which are gases at room temperature). However, all compounds have their own set of properties, such as the temperature at which they melt or boil.
When a compound is formed, energy is usually given out or taken in as heat. When a mixture is formed, no heat is given out or taken in.
Carbonates, such as limestone, have been laid down as thick deposits all over the Earth.
The cubic crystals are iron pyrites, a form of iron sulphide.
The transparent crystals are quartz (a form of silica, or silicon oxide).
The black mineral is sphalerite (a form of zinc sulphide).
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