How can an oxygen atom become an ion with a charge of -2?
2 Answers
Oxygen is in group six in the periodic table so it has six electrons in its valence shell. This means that it needs to gain two electrons to obey the octet rule and have a full outer shell of electrons (eight). Because electrons have a charge of 1-, adding two electrons would make the charge of the oxide ion 2-.
Oxygen takes the electron density from other atoms when it forms two bonds, to become a negative two ion.
Explanation:
Oxygen has the second highest electronegativity of any element. When Oxygen forms a bond it pulls the electron density of the bond closer to the Oxygen and away from the other element. (Florine is an exception to this principle. ) This causes Oxygen to have a negative charge and the other atom a positive charge.
Oxygen has an electron configuration of
This leaves Oxygen with two p orbitals that have only 1 electron. These unpaired electrons can form two bonds. Each of the bonds creates a negative one charge giving Oxygen a charge of -2.
