Clarendon Laboratory, University of Oxford

On 24 September 2007, the Clarendon Laboratory, the Physics Centre of the University of Oxford, was awarded Chemical Landmark status for its contribution to science and in particular for the discovery in 1914 of the concept of the atomic number by H G J Moseley, fundamental to the whole of inorganic chemistry.

The discovery was made by a 26 year old research worker, Henry Gwyn Jeffreys Moseley, who had graduated from Trinity College in 1910. After graduating, he worked for a while at Manchester with Professor Rutherford, the discoverer of the atomic nucleus, before returning to Oxford to continue his physics research. This was an exciting time for atomic physics.

Moseley set out to investigate the relationship between the frequency of the x-ray lines and the metal of the anode. He devised an apparatus for bombarding with high voltage electrons all the known metals from aluminium to gold and then, using Braggs Law, measuring the wavelengths of the resultant x-rays. From these values he was able to calculate the corresponding frequencies and subsequently the atomic number of the element. Moseley's handwritten graphs are still held in the Clarendon Laboratory archives.

The importance of Moseley's work for chemistry cannot be overstated. The understanding of chemical bonding depends heavily on the concept of atomic number, along with the structure of the atom as first propounded by Bohr and subsequently refined by quantum theory. In addition to its theoretical importance, Moseley's work also laid the ground for non-destructive chemical analysis by means of x-ray emission spectroscopy. This is now a major tool of analytical chemistry.

Sadly, just one year after his pioneering research, Henry Moseley was killed in the First World War at the battle of Gallipoli, aged just 27 years.

Following a lecture on the work of Henry J G Moseley by Professor E Joseph Nordgren, Professor of Soft X-Ray Physics, University of Uppsala and Member of the Royal Swedish Academy of Sciences, RSC President, Professor Jim Feast presented the Chemical Landmark to Vice-Chancellor, Dr John Hood.

The inscription on the plaque reads:

Clarendon Laboratory

where H G J Moseley (1887-1915) completed his
pioneering studies on the frequencies of
X-rays emitted from the elements.
 
His work established the concept of atomic number
and helped reveal the structure of the atom.
He predicted several new elements,
and laid the ground for a major tool 
in chemical analysis.

24 September 2007