Unit 1.4: Bonding
Ionic bonding – a bond formed by the electrical attraction between positive and negative ions. These are overall neutral because the cation and anion make it overall neutral.
Covalent bonds- has a pair of electrons with opposed spins shared between two atoms with each atom giving one electron.
Co-ordinate bond – a covalent bond in which both electrons come from one of the atoms.
Metallic bonding – a lattice of positive ion are held together by a sea of delocalised electrons.
Intramolecular bonding – this is the bonding between molecules (covalent, ionic, metallic)
Intermolecular bonding – the bonding between molecules (Van der Wals, Hydrogen bonds)
Electronegativity is a measure of the tendency of an atom to attract a bonding pair of electrons in a covalent bond.
- Occurs between metals and non-metals
- Involves transferal of electrons from metal atoms to non-metal atoms
- Positive and negative ions are formed
- Electrostatic attraction holds positive and negative ions together – this is an ionic bond
- Always exist in a lattice structure
Property of ionic compounds
Do not conduct electricity when solid
Ions are fixed in position by strong ionic bonds. When molten or dissolved in water, ions are free to move.
High melting/boiling points
Giant lattice structure held together by strong electrostatic attraction between ions which requires lots of energy to break
Brittle and shatter easily
Small displacement causes contact between ions of same charge which repel and structure shatters
Dissolve in water
Polar water molecules pull ions away from lattice and cause it to dissolve
Sodium chloride is an example of an ionic crystal with the above properties. (A crystal is just a solid with a regular arrangement)
- 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
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
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…