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Recall An element is a substance made up of only one type of atom.

Atoms rarely exist on their own; instead, they are joined together by chemical bonds to form compounds.


A compound is made of atoms of different elements joined together by chemical bonds.

Remember that you can describe an element with a symbol. Compounds are described by chemical formulae. 

For example, water is a compound formed when two hydrogen atoms bond to an oxygen atom. The chemical formula for water is H2O.

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