Elemental weigh in

The International Union of Pure and Applied Chemistry has released another revision to standard atomic weights. In total, 19 elements have been found to have gained or lost a little weight. And we do mean a little.

Atomic weights are often thought of as static, but they vary as new sources of elements are discovered, changing the ratio between different isotopes. In the latest weigh in, selenium and molybdenum gained and lost the most weight, selenium gaining 0.011 atomic mass units and molybdenum losing 0.01. For both elements that’s a change of around 0.01%.

While such small changes will not affect most chemists’ calculations, as techniques get more and more accurate it might help if atomic weights are as accurate as they can be.