Covalent Bonding
- Occurs between non-metals
- Involves the sharing of outer electrons between atoms
- Can form simple covalent (molecular) or giant covalent (macromolecular) structures
| Property of simple covalent compounds | Explanation |
| Do not conduct electricity | No ions or delocalized electrons involved. |
| Low melting/boiling points | Weak intermolecular forces – covalent bonds do not need to be broken. |
Iodine is an example of a molecular crystal with the above properties. The iodine atoms pair up to form I2 molecules, held together by strong covalent bonds. Intermolecular forces between the I2 molecules hold the crystal together.
There are two main carbon macromolecular structures: graphite and diamond. These are allotropes of carbon.
The carbon atoms in graphite are arranged in sheets of flat hexagons. The carbon atoms form three bonds each and the fourth outer electron of each carbon atom is delocalized.
| Property of graphite | Explanation |
| Slippery/Soft (used in pencils) | Weak Van der Waals forces between layers that are easily broken. |
| Strong and lightweight | Layers are quite far apart which gives graphite a low density |
| Conducts electricity | Graphite has 1 delocalized electron per carbon atom as it only forms three bonds so can conduct electricity along the hexagonal sheets. |
| High melting/boiling points | Strong covalent bonds in hexagon sheets – sublimes at over 3900K. |
| Insoluble | Covalent bonds too difficult to break |
The carbon atoms in diamond are arranged in a tetrahedral shape. The carbon atoms form four bonds each, which gives it a rigid crystal lattice structure.
| Property of diamond | Explanation |
| High melting point | Strong covalent bonds in crystal lattice structure. |
| Hard | Rigid crystal structure |
| Does not conduct electricity | All electrons are used in bonding, so no delocalized electrons to conduct electricity. |
| Insoluble | Covalent bonds too difficult to break |
A dative or co-ordinate bond is when one atom donates both the electrons in the covalent bond eg N to H+ in NH4+ (ammonium ion)
Definition of covalent bond: A shared pair of electrons between two atoms
