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Ok so gadolinium is smack-*** in the middle of the 4f series. It’s
perhaps most famous for the fact that it’s used as a contrast reagent in
MRI machines. So if you need a full body scan, a doctor will come along
an inject you with a solution which contains a bit of gadolinium and what
it basically does is that it changes the way that molecules, water
molecules react in your body when they are scanned and then you can
see the contrast between healthy tissue and, perhaps, unhealthy tissue
and then that aids the doctors in their assignment.
The thing about the lanthanide series is that it’s probably the best
example of a smooth contraction in size as you move from the left-hand
side to the right-hand side and you lose about 25% of the radius of the
atoms as you move from the left to the right and this is called the
‘lanthanide contraction.’ This is actually what’s responsible for 2nd and 3rd
row transition metals having very similar types of chemistry by group
even though actually they should be quite different. The 3rd row should
be much larger but, because of the ‘lanthanide contraction’, that
increase in size is counterbalanced so they actually end up being more-
or-less the same size as their 2nd row counterparts.
Even chemists sometimes wonder how people can get excited about
particular parts of chemistry, and the rare earth elements are elements
which, those who are not working in the area don’t always see why it can
be very exciting. So when I was a student I saw an advertisement in the
lab where I was working about a lecture about the oxidation states of the
rare earth elements, and the relative stability of two of the oxidation
states by a chemist called David Johnson, who in those days worked for
the Open University. And, I went to this lecture because I couldn’t
imagine how anybody could make it interesting, and it was really
fascinating! He was so enthusiastic and so on, by the end, I rushed out
really quite excited I went and bought this book which has been sitting
on my bookshelf ever since and has been quite useful for teaching some
of my students.