My science exam is tomorrow, I will be tested on elements mixture compound. please give me some tips and notes.

All elements are pure substances that contain atoms of
only one kind. These are the elements listed on the periodic table.  All elements have
basically the same physical and chemical
properties.

Compounds are pure substances that contain
atoms of more than one kind that are chemically bonded together and cannot be separated
by simple, mechanical means.  The ratio of the atoms in any compound are always in the
same fixed ratio. The chemical and physical properties of compounds are always the
same.  Salt is an example of a compound.

Mixtures contain
two or more  pure substances that are not chemically bonded together. The pure
substances can be separated into their individual components.  The physical and chemical
properties of mixtures are not fixed and the ratio of the various substances can vary
widely.  Salt water, sand + water, food, etc. are all examples of
mixtures.