Summary

• There are two main types of subunits that make up matter: atoms and molecules.

• Atoms are the most basic type of subunit.

• Molecules consist of two or more atoms held in a fixed arrangement by chemical bonds.

• Matter can be classified into pure substances or mixtures, based on the number of different subunits it contains.

• Pure substances are made up of one type of subunit.

• Mixtures are made up of more than one type of subunit.

• Pure substances can be classified into elements or compounds, based the number of different atoms they contain.

• Elements are made up of one type of atom.

• Compounds are made up of more than one type of atom.

• Pure substances (elements and compounds) have fixed properties.

• Mixtures have variable properties.

• Elements cannot be separated into other substances.

• Compounds can be chemically separated into their component elements.

• Mixtures can be physically separated into their component substances.