What is the charge that results when oxygen becomes an ion?

Dec 14, 2015

$- 2$
Oxygen has $6$ valence electrons. To fill up the valence shell, which (when in oxygen's row) has $8$ electrons, an oxygen atom wants to gain $2$ electrons.
Since every electron has a single negative charge, the addition of two electrons results in an oxygen ion with a charge of $- 2$.