Originally posted by Kahynickel:
The electronegativity of Nitrogen is 3.0 and of chlorine is 3.2.
I am not sure about the exact values. anybody knows the actual
values.
There are multiple systems of electronegativity ratings using different experimental systems and calculation methods. As such, you will come across different systems (eg. Pauling, Mulliken, Allred–Rochow, Sanderson, Allen, etc) giving you different electronegativity values for each element. Some systems rate Cl as being more electronegative than N, while other systems rate N as being more electronegative than Cl.
For A level purposes, N is regarded as more electronegative than Cl, and as such, only NH groups (in addition to HF and OH groups), and not HCl, are considered capable of donating H bonds.
A level students are not expected to memorize electronegativity values from any particular system. Cambridge may give electronegativity values (from any of the different electronegativity systems) in the A level question itself, to examine if the A level candidate is able to interpret the relative values of the various elements. For instance :
Carbonyl sulfide has the formula O=C=S. If the electronegativity of O, C and S are 3.5, 2.5 and 2.4 respectively, which bond is more polar? The O=C bond or the C=S bond? Indicate the partial charges and dipoles on the O=C=S molecule.