Question

Since Lewis structures use valence electrons, where do the extra electrons for polyatomic ions come from? for example SO42- Sulfur has 6 and oxygen has 6x4, so there are 30 valence electrons available, but 32 for the lewis structure

Answer 1

Double bonds. There's two I think.

Answer 2

You have to add the electrons for the charge. -2 = add two electrons

Answer 3

in forming polyatomic ions, the neutral atoms have to pick up electrons from somewhere, but we usually don't worry about where. The atoms would have to take electrons from another atom willing to lose them, like calcium, which is partly why we never see reactive metals in their elemental, zero oxidation state, in nature. we always see them as ionic oxides, carbonates, sulfates, etc etc.