Which one of the following alternatives lists the atoms of chlorine, magnesium, neon and phosphorus in order of increasing first ionisation energy? A - VCE - SSCE Chemistry - Question 18 - 2006 - Paper 1

To determine the order of increasing first ionisation energy, we consider the electronic configurations and general trends in the periodic table.

1. Magnesium (Mg): As a group 2 element, it has a relatively low ionisation energy due to the larger atomic radius and lesser effective nuclear charge compared to non-metals.
2. Phosphorus (P): Being a group 15 non-metal, it has a higher ionisation energy than magnesium because non-metals generally have higher ionisation energies compared to metals.
3. Chlorine (Cl): A group 17 non-metal, chlorine has an even higher ionisation energy than phosphorus as it is more electronegative and has a stronger attraction to its outer electrons.
4. Neon (Ne): This noble gas has the highest ionisation energy of the group due to its stable electron configuration, which requires significantly more energy to remove an electron.

Thus, the order based on increasing first ionisation energy is: Mg < P < Cl < Ne.