Summary

• Atoms are the fundamental subunits of matter.

• They may exist individually (in some elements) or joined to other atoms by chemical bonds, forming molecules or lattices (in most elements and all compounds).

• Molecules are discrete structures containing two or more atoms bonded together in a fixed arrangement.

• Molecules can consist of one type of atom, or more commonly, more than one type of atom.

• Lattices are continuous networks of atoms joined by chemical bonds.

• As with molecules, lattices can consist of one type of atom, or more commonly, more than one type of atom.

• Elements and compounds are both pure substances as they are made up of one type of chemical subunit.

• Elements are composed of one type of atom.

• These atoms may exist separately, as molecules or as a lattice.

• Compounds are composed of more than one type of atom.

• These atoms may exist as molecules or as a lattice.

Some molecules, such as proteins, can contain thousands of atoms.

(Image: Splette, Wikimedia Commons)