Chemical reactions produce new substances. Elements may react together to form compounds, because their atoms join to other atoms using chemical bonds.
For example, iron and sulfur (often spelt 'sulphur') react together to form a compound called iron sulfide (often spelt 'sulphide'), and sodium and oxygen react together to form sodium oxide.
The significance of electrons in bonding
Chemical bonds are produced by a change in position of outer electrons in the reacting atoms.
Bonds can form when: