Introduction to Chemistry – Grade 10 Review
Oxidation number: The apparent charge assigned to an
ion that indicates the movement of an electron in a
compound. (A.k.a. bonding capacity or the charge)
Valence electrons: Electrons in the outermost orbits of
an element. These are the most important with respect
to the element’s reactivity.
Oxidation number vs. valence electrons
Groups
IA IIA IIIA IVA
VA
VIA
VIIA
VIIIA
Ox. #
1+
2+
3+
4+/-
3-
2-
1-
0
Val. e-
1
2
3
4
5
6
7
8


If the charge on an ion is positive it has lost electrons,
which are negatively charged.
If the charge on an ion is negative it has gained
electrons.
Example: Magnesium is in group IIA on the periodic
table. It has 12 electrons and 12 protons. Two of the 12
electrons are in the outer shell, (valence electrons).
When magnesium bonds with oxygen it will lose it’s two
electrons and end up positively charged. Therefore
magnesium’s oxidation number is 2+. What is the valence
number and oxidation number for oxygen?
Mg
O
Mg
O