Atoms & ions

All nuclei with more than 83 protons are unstable. But size isn't the only factor- the neutron/proton ratio must be just right for a nucleus to be stable. The optimal ratio is about 1:1 for light nuclei; it increases to about 1.5:1 for bismuth.

Counting particles


Compounds containing different isotopes react at slightly different rates. For example, electrolysis of water is faster for water containing 1H than for water with 2H. The difference in reaction rate is used to isolate "heavy water".

Weighing atoms

The first mass spectrograph was built in 1919 by F. W. Aston, who received the 1922 Nobel Prize for this accomplishment. Schematic of a mass spectrometer

Predicting ion charges

Naming monatomic ions