How do you know when the central atom in a lewis structure will have more than 8 electrons?

One particular example in mind is BrO3F. The structure should have 32 electrons, and it does when Br has a single bond with the other atoms and their formal charge cancels out to have a formal charge of zero.

To know when a central atom in a lewis structure will have more than 8 electrons it is important to know where is the element at the periodic table and the orbital configuration of the atom.

Explanation:

The octet rule establishes that an atom could win, lose, or share electrons with other atoms till every atom have eight valence electrons. However exist exceptions to the octet rule. Some elements like Be, B and Al are stable with only six valence electrons because these three elements are small and with low electronegativity. On the other hand, some elements from the 3d orbital could expand their octet and still be stable, like S in SF6. This happens because elements from 3d orbital have enough space to suit more electrons.