Among those to have had their standard atomic weights adjusted are elements like aluminium, fluorine, arsenic, caesium, cadmium and selenium.
The changes have occurred due to a greater understanding of the prevalence of different versions of the atoms, known as isotopes.
Each isotope of an atom has a slightly different mass due to the number of neutrons it contains.
The standard atomic weight is then calculated by taking into account the abundance of each isotope to give an average weight for an atom.
These are then displayed on the Periodic Table that appears in text books around the world.
Improved measurements and better data on the proportions of different atomic isotopes meant that nineteen of the atoms in the periodic table needed to be reassessed.
While some of the atoms were found to have an average weight that was a tiny fraction greater than previously calculated, others decreased.
The changes mean the total weight displayed on a Periodic Table has increased by 0.003640021, although clumped the changes together in this way means very little.
As atomic weights are relative they do not carry units.
In reality the tweaks to the standard atomic weight are unlikely to result in any fundamental changes in science and their main value lies purely from an academic point of view.
Only the most detailed of textbooks are likely to have to change the values, with atoms like thorium gaining just 0.000322 in weight.
Cadmium, however, has lost 0.0026 of weight in the reassessment. Gold was also reassessed but it was found to have the same atomic weight as before.