Something to think about

The IB uses Pauling’s scale of electronegativity. It was Linus Pauling who first proposed the idea that the bonding electrons pair between two different atoms is not shared equally. If the electrons are in the same outer electron energy level in both atoms then they will tend to be closer to the atom with the greater number of protons in the nucleus resulting in a polar bond. Similarly the closer the outer electron energy level is to the nucleus then the greater the electronegativity. Thus fluorine is the most electronegative element of all. Pauling’s scale was first proposed in 1932 and is a relative scale so has no units.

In 1934 Robert Mulliken (of the ‘oil drop experiment’ fame) proposed that electronegativity could be measured as a quantitative value measured in kJ mol^-1. He arrived at the value by taking the arithmetic mean of the absolute values (i.e. ignoring the + or – sign) for the first ionization energy and the electron affinity of an element. You could use Section 8 of the IB data booklet to work out values based on this relationship. For example:

It is an interesting exercise to convert these to the Pauling scale by using the fact that fluorine (1005 kJ mol⁻¹) is equivalent to 4.0 on the Pauling scale. By scaling the other values chlorine (800 kJ mol⁻¹) becomes 800/1005 x 4.0 = 3.2, bromine becomes 733/1005 x 4.0 = 2.9 and by doing similar calculations hydrogen becomes 2.7 and sodium becomes 1.1. These values do compare quite well with Pauling’s scale F (4.0), Cl (3.2), Br (3.0), H (2.2) and Na (0.9). Milliken’s absolute scale is not often used, partly because the electron affinities of some elements are not well-known. Even so perhaps it is worth realising that there is an absolute scale as well as Pauling’s relative scale. Maybe this could provide some fertile ground for a non-experimental individual scientific investigation for your IA?