http://www.ck12.org Chapter 9. Covalent Bonding
a gas at temperatures above 3500°C. The properties of these and other types of solids are discussed further in the
chapter,States of Matter.
An exciting demonstration of the poor conductivity of covalent bonds in a rubber stopper can be seen at http://educa
tion.jlab.org/frost/stopper.html.
Lesson Summary
- The difference in electronegativity between the two atoms in a bond determines the type of bond that is formed.
A small difference means that the sharing of electrons is equal, and the bond is nonpolar covalent. A larger
difference means that sharing is unequal, and the bond is polar covalent. A very large difference means that
one or more electrons are transferred, and the bond is ionic. - Polar molecules result when polar bonds are arranged in a nonsymmetrical molecular geometry. A molecule
such as CO 2 contains polar bonds, but due to their arrangement, the individual dipoles cancel out to make the
overall molecule nonpolar. - Intermolecular forces, such as dipole-dipole forces, London dispersion forces, and hydrogen bonds, are weak
forces that exist between molecules. - The properties of molecular and ionic compounds are generally different because of the different nature of
their chemical bonds.
Lesson Review Questions
Reviewing Concepts
- What range of electronegativity differences between the two bonded atoms are classified as polar covalent?
- What is a diatomic molecule? Give an example.
- What is meant by the symbolsδ+ andδ−in a structural formula?
- Can a nonpolar molecule contain polar covalent bonds? Explain.
- List the three main types of intermolecular forces from weakest to strongest.
- For a molecule to undergo hydrogen bonding, it must have a hydrogen atom covalently bonded to an atom of
one of three elements. What are those three elements? - Why are molecular compounds poorer conductors of electricity than ionic compounds even when both are
dissolved in water?
Problems
- Arrange the following bonds in order from least polar to most polar: Al−N, Br−C, P−H, Cl−F, K−O.
- For each molecule below, determine the molecular geometry and state whether the molecule is polar or
nonpolar.
a. CBr 4
b. H 2 S
c. BF 3
d. PCl 3
e. SeF 4
f. BeCl 2
g. ClF 3
h. CH 2 Cl 2