Tuesday was World Water Day 2011 and the theme for this year was ‘Water for Cities’. The theme for this weeks blogs posts will therefore be all about water.
So far, we have been focusing on the fact that water has a much higher boiling point than is predicted and that the reason could be pinned down to electronegativity.
Image kindly reproduced according to the licence at: http://en.wikipedia.org/wiki/File:3D_model_hydrogen_bonds_in_water.jpg
You may also remember that yesterday I posted a question asking:
‘What causes electronegativity?’
Well, electronegativity is caused by the size of the atom, the nuclear charge (or the number of protons) and the distance of the outer electrons from the nucleus.
Small atoms will have electrons relatively close to the nucleus. There is little shielding of the outer electrons by electrons in lower energy levels.
Relatively speaking, they will have a much higher attraction for other electrons than, say, a large atom.
Although a large atom may have a large nucleus (and hence, a large number of protons), its outer electrons will be much further away from the nucleus and this means that the attraction for the outer electrons and the nucleus will be much weaker.
It will also have many more inner energy levels shielding the outer electrons.
Electronegativity is one of the most important concepts you study at IB Chemistry and it can explain many phenomena.
It is also one of the factors that makes water so special!