1.3 IONS AND THE OCTET RULE
A stable octet is an arrangement that some atoms have when their valence shells are
completely filled. Noble gases have a filled shell of eight electrons. Helium is the exception,
and has 2 electrons in its valence shell. The Octet Rule is followed when atoms of other
elements must combine with other atoms in order to achieve a stable electron arrangement.
Atoms can achieve stability in one of three ways: by sharing their electrons, losing or
gaining electrons. An ion (a positive or negatively charged atom) occurs when the atom loses or
gains electrons. It depends on the number of valence electrons.
Cations are positively charged ions.
 They are usually formed from the metals on the left side of the periodic table.
 These elements tend to have a few electrons in their valence shell.
 Metals generally tend to lose those electrons.
Example 1:
11p+
12n0
+
11p+
12n0
energy
-
+e
Anions are negatively charged ions.
 They are usually formed from the non-metals on the right side of the periodic table.
 These elements tend to have more than four electrons in their valence shell.
 Non-metals generally tend to gain electrons.
 Non-metal anions are named by replacing the end of the element’s name with -ide
Example 2:
8p+
8n0
+ 2e-
8p+
8n0
+
energy
Multivalent Elements
Some elements are able to form more than one stable ion. The majority of these elements are
transition metals (elements found in the middle of the periodic table). There are two ways to
name these multivalent ions – The Latin way and the IUPAC way
Ex. Copper (I) or cuprous is Cu+ and Copper (II) or cupric is Cu2+
Polyatomic Ions - Ions that consist of
more than one kind of atom. Some
polyatomic ions occur naturally and are
important to health, while others can be
made synthetically.
Example: Calcium phosphate is found in
bones and teeth. Hydrogen carbonate
help to regulate the pH of the blood.
Table 3 – Some Important Ions in the Human Body (Page 21)
Ion
+
Na
K+
Role
Source
salt, cheese, preservatives
Bananas, milk, potatoes
Ca2+
Milk, cheese, spinach
Fe3+
Kidney beans, asparagus, pine nuts
Mg2+
Green plants, nuts, grains
ClIHOMEWORK: Page 22 #1-8
Salt
Fish, dairy products, iodized salt