Chemistry Reference
In-Depth Information
1234567
8
9
Bonding and Molecular Structure
Lesson 4 - 1: Types of Bonds
In Chapter 3 we discussed the octet rule, which states that an atom
with a full valence shell (8 electrons in most cases) is considered relatively
stable. Atoms tend to gain, lose, or share electrons in order to complete
their valence shells and obtain the configuration of a noble gas. What an
atom does in order to complete its valence shell depends upon the situa-
tion that it is in. Recall that oxygen has 6 electrons in its valence shell. In
some situations, oxygen is able to gain 2 additional electrons, for a total of
8 valence electrons, to become the oxide ion (O
2-
). This anion (negative
ion) may then attach to one or more cations (positive ions), forming one or
more ionic bonds. Compounds formed in this way are called ionic compounds,
as shown in the following reactions:
CaO
2Na
+
+ 0
2-
Na
2
O
In other situations, the neutral oxygen atom may share electrons with
one or more other atoms, in order to “act” as though it has a complete
valence shell part of the time. These shared electrons represent covalent
bonds and result in the formation of molecular compounds, as shown here:
Ca
2+
+ O
2-
N
2
+ O
2
2NO or 2H
2
+ 0
2
2H
2
O
The type of bond, and therefore the type of compound, that an atom
will form in a given situation depends upon the relative electronegativities of
the elements involved. The electronegativity of an element is a relative mea-
sure of its attraction for bonding electrons. The scale for electronegativity
was based on the most electronegative element, fluorine, which has an
