REACTIONS AND COMPOUNDS
New substances are formed by chemical reactions. When elements react together to form compounds their atoms join to other atoms using chemical bonds.
Ionic bonds
Compounds formed from metals and non-metals consist of ions. Ions are charged particles that form when atoms (or clusters of atoms) lose or gain electrons:
- metal atoms lose electrons to form positively charged ion
- non-metal atoms gain electrons to form negatively charged ions
The ionic bond is the force of attraction between the oppositely charged ions.
Covalent bonds
Two non-metals share an electron to form covalent bonds that hold the atoms together to form molecules.
Chemical formulas
The chemical formula of a compound shows how many of each type of atom join together to make the units which make up the compound. For example, in iron sulfide every iron atom is joined to one sulfur atom, so we show its formula asFeS. In sodium oxide, there are two sodium atoms for every oxygen atom, so we show its formula as Na2O. Notice that the 2 is written as a subscript, so Na2O would be wrong.
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