Elements
and compounds are substances because we know exactly what is in them.
Elements are only one kind of atom and have a symbol. Compounds have a
formula telling us exactly how many of what kind of atom make up that
compound
Solutions, homogeneous mixtures, not only contain 2 compounds, but we do
not know how much of each. We can make salt water with one grain of
salt in a cup of water or a drop of water in a cup of salt. Mixtures do
not have a formula because they can be any concentration.
