There are Certain Formulas You Never Reduce

The most common ones are with mercury(I), which is Hg22+.

It is NEVER Hg+ by itself. It ALWAYS comes as a pair. There are reasons for this behavior, but that is beyond the scope of this work. Note: if anybody has found an explanation on the Web, let me know at, so I can set up a link. Thanks. And now, back to chemistry.

Example #1: mercury(I) chloride

The formula for this compound is Hg2Cl2. It is not HgCl. You will be marked wrong on a test for doing so.

Example #2: mercury(I) nitrate

The formula for this compound is Hg2(NO3)2. Once again, it is not reduced. Why? In nature, mercury(I) comes in a set of two atoms, NOT just one.

The corresponding mercury(II) formula for the two examples would be HgCl2 and Hg(NO3)2.

The second major category is peroxide, which is O22¯.

Example #3: hydrogen peroxide

The formula is H2O2 and it is not reduced to HO. Why? Same reason as above, peroxide travels as a group of two oxygen atoms, not one.

Example #4: sodium peroxide

The formula is Na2O2.