Untitled - Kelly Walsh High School

130 CHEMISTRY FOR THE UTTERLY CONFUSED
does not give you an indication of the actual shape of the molecule. (For a discussion
on the shape of molecules, see Chapter 10 on Molecular Geometry and
Hybridization.) Below are the empirical, molecular, and Lewis structural formula
of hydrogen peroxide, H 2O 2.
HO
Empirical Formula
9-2 Electronegativity
H 2 O 2
Molecular Formula
O O
H
H
Structural Formula
In many cases, you will need to predict the type of bond present. We will be giving
you several tips along the way to help you decide. Electronegativity is a tool
that you can use in predicting bond type. This tool will also help you to make
other predictions.
Electronegativity is a measure of the attractive force that an atom in a compound
exerts on electrons in a bond. You may find electronegativity values in a
table in your textbook. There are two trends in these values. In general, electronegativities
increase going towards the right on the periodic table (excluding
the noble gases). The values also increase towards the top. These trends combine
and lead to fluorine being the most electronegative element. The nearer an
element is to fluorine, the higher its electronegativity.
You will need to know the electronegativity difference between the atoms. The
key to the type of bond formed is this difference. A mostly ionic bond is present
when there is a large electronegativity difference. “Large,” according to
Pauling, refers to a difference greater than 1.7. If the difference is zero, the
bond is covalent. Anything in between these extremes is polar covalent.
(See Section 9-4 for a discussion of these bond types.) You do not need to know
the actual electronegativity values. The further apart two elements appear on
the periodic table, the greater the electronegativity difference. Widely separated
elements usually form ionic bonds.
Quick Tip
If the atoms are widely separated on the periodic table (metals and nonmetals),
the bonding is most likely ionic. Nonmetals close together are likely to form
covalent bonds.