Elements:
a pure substance containing only one kind of
an element be separated into simpler materials (except during nuclear reactions).
over 100 existing elements are listed and classified on the

compounds:
a pure substance containing two or more kinds of
the atoms are combined in some way.
compounds be separated by physical means.

mixtures:
two or or not chemically combined.
mixtures can be uniform( and are known as solutions
mixture can also be non-uniform (called