Argh I was a little worried (okay a lot) when I was exploring Yahoo answers and I couldn't answer a lot of Bio and Chem questions. So I went to Chemguide and read a bit.
Down a group as the size of an atom increases the valance electron is further away from the nucleus, so the attraction between the electron and the nucleus is weaker. EA decreases down a group. However fluorine is anomalous.
From http://www.chemguide.co.uk/inorganic/group7/properties.html#top :
There is another effect operating. When the new electron comes into the atom, it is entering a region of space already very negatively charged because of the existing electrons. There is bound to be some repulsion, offsetting some of the attraction from the nucleus.
In the case of fluorine, because the atom is very small, the existing electron density is very high. That means that the extra repulsion is particularly great and lessens the attraction from the nucleus enough to lower the electron affinity below that of chlorine.
No comments:
Post a Comment