So the common name of cations requires an older naming method, and we'll use this older naming method for cations that possess multiple charges. We won't be using Roman numerals, we'll be using an older system for naming these particular types of cations. Now, under this system, the lesser charge of the cation uses the suffix or ending of -ous, whereas the greater charge uses the suffix of -ic. So, how exactly do we approach this? Here we have metal cation suffixes. We have the element name, ion symbol, systematic name, and then our common name. So, we're going to say here that chromium exists as either Cr2+ or Cr3+. The systematic name is what we've learned earlier. Because they possess multiple charges, we can use Roman numerals under the systematic names. This one will be chromium(II) because it's 2+, and this would be chromium(III) ion. Now, under the common naming system, we're going to say that this +2 is the lesser charge. And because it's the lesser charge, it uses the ending 'ous'. So this would be chromous ion. +3 is the higher or greater charge of this particular ion, so it uses the ending 'ic', so this would be chromic ion.

Copper can be +1 or +2, so we're going to say here this is copper(I) and this is copper(II) ion. Here would be cuprous ion, and this would be cupric ion. Iron can be Fe2+ or Fe3+, so this would be iron(II), and this would be iron(III). You might be noticing that, hey, it's iron here, but it's ferrous here and ferric there. That's because the common name is also tied to Latin names for some of these elements. Realize that copper uses the symbol Cu, iron uses Fe. That's because these element symbols are based on their Latin root names, and the common name highlights this fact. So, iron Fe2+ is the lesser charge, so this is ferrous ion. Fe3+ is the higher charge, so this is ferric ion.

Mercury is a little bit weird. Mercury can exist as a pair and together they are 2+. That means each one is actually +1. So this would be mercury(II) ion. This would translate to mercurous ion and mercuric ion. Then finally, we have tin which is Sn. Again, Sn here doesn't match the name Tin; that's because Sn is based on the Latin name for it. So, tin can be Sn2+ or Sn4+, so this would be tin(II) and tin(IV), which would translate to stannous ion and stannic ion. So, just remember, we use this common naming method for cations with multiple charges. The lower charge uses the ending of 'ous'. The higher charge uses the ending of 'ic'.