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Geochemistry determining atomic weight


How isotopes affect atomic weight
Norman Greenwood Scientist
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The important point that I want to now go on to talk about is that pretty much until this time, following Dalton, an atom of an element had a characteristic weight and all the atoms in... of that element... had that weight.

Once we had isotopes this varied and it explained, for example, why chlorine has an atomic weight of 35.5 – that couldn’t be explained on most ordinary theories until isotopes were discovered. And it was that chlorine had an isotope 35 and 37 and it was a mixture of the two of them, so 35.5 meant that there was more 35 than 37, but it was not a whole number. That was creating a problem. The problem of oxygen was there, but much worse, it turned out that as we did – or had – better and better results and measurements, it became clear that for many elements, the atomic weight did, in fact, vary, and it varied for one of several fairly simple reasons.

Norman Greenwood (1925-2012) was born in Australia and graduated from Melbourne University before going to Cambridge. His wide-ranging research in inorganic and structural chemistry made major advances in the chemistry of boron hydrides and other main-group element compounds. He also pioneered the application of Mössbauer spectroscopy to problems in chemistry. He was a prolific writer and inspirational lecturer on chemical and educational themes, and held numerous visiting professorships throughout the world.

Listeners: Brian Johnson

Professor Brian FG Johnson FRS, FRSE, FRS Chem, FAcad Eu, FAS. Professor of Inorganic Chemistry University of Edinburgh 1991-1995, Professor of Inorganic Chemistry University of Cambridge 1995-2005, Master Fitzwilliam College Cambridge 1999-2005. Research interests include studies of transition metal carbonyls, organometallic chemistry, nano- particles and homogeneous catalysis. Professor Johnson is the author of over 1000 research articles and papers.

Tags: John Dalton

Duration: 1 minute, 27 seconds

Date story recorded: May 2011

Date story went live: 25 November 2011