1. Periodicity Trends in Bonding Across Period 3

2. On crossing period 3, the ionisation energies of the elements increase so it becomes more difficult to remove electrons and form metallic structures. Covalent bonding becomes more common on crossing a period from left to right.

3. Na metallic Mg metallic Al metallic Si covalent P covalent S covalent Cl covalent Ar - The trends in intramolecular bond type can be seen in the following table:

4. Argon Argon is a noble gas and will form neither metallic nor covalent bonds. The ionisation energy is very high so metallic bonding is not possible. There are no unpaired electrons so covalent bonding is not possible. It forms no bonds and exists as a free gaseous atom.