Atomic weights revision changes periodic table
A magnificent period piece from mid-19th-century Russia has just received a bit of a renovation. Five elements at the heart of the periodic table will never look the same again, following an update to their atomic weights.
“Your chemistry teacher probably said to you ‘atomic weights are constants of nature’, but nothing could be further from the truth,” says Tyler Coplen, director of the Reston Stable Isotope laboratory in Virginia. In fact, the atomic weight of some elements varies depending on where you are on Earth.
Most of the mass of an atom resides in its nucleus, composed of protons and neutrons (with the exception of hydrogen, whose nucleus consists of a single proton). The number of protons in the nucleus determines what atom you are dealing with: all carbon atoms have 6 protons, all oxygen atoms have 8, and so on. But the number of neutrons can vary from atom to atom of the same element. Atoms of the same element but with different numbers of neutrons are called isotopes.
Every element has a number of unstable isotopes, which break apart through radioactive decay, but some elements have more than one stable isotope too. This is where chemists run into problems when it comes to defining the atomic weight…
This has led the guardians of the periodic table – the International Union of Pure and Applied Chemistry (IUPAC) – to decide that the atomic weights of bromine and magnesium are better accommodated by intervals than by single numbers… While they were at it, the IUPAC also took the opportunity to tweak the atomic weights of three more elements: germanium, indium and mercury.