Adapted from Linus Pauling, “The Nature of the Chemical Bond: 3rd Edition,” ©1960.
1 What principles dictate the relationships between
molecules? There are many factors at work, but these
interactions also depend indirectly on a principle known
as electronegativity. Although this is an atomic property,
it generates molecular 2 forces, that cause many of the
phenomena we observe every day.
3 Electronegativity, the measure of an atom’s affinity
for electrons, generally determines the type of bond
present between two atoms. A single bond between atoms
consists of two electrons. If the two atoms have similar
electronegativities, they share the two electrons equally
and form a nonpolar covalent bond. If two atoms have
significantly differing values of electronegativity, there are
two possible bond types: polar covalent and ionic. While
other factors also 4 corrupt the determination of bond
type, a difference in electronegativity between the values of
0.5 and 1.6 usually 5 result in a polar covalent bond, while
a difference of more than 2.0 usually results in an ionic
bond. In a polar covalent bond, the two bonding electrons
are shared 6 unequally, in an ionic bond: both electrons
are completely transferred to the more electronegative
atom. For example, the bond between oxygen (O) and
hydrogen (H) is classified as a polar covalent bond, because
they share the two bonding electrons unequally. This
polar bond type is partially caused by the difference in
electronegativities: 7 hydrogen has an electronegativity
of 2.20, while oxygen has an electronegativity of 3.44. When
the electronegativity of the hydrogen is subtracted from the
electronegativity of the oxygen, the difference is 1.24.
When a hydrogen atom is bonded to nitrogen, oxygen,
or fluorine, this particular polar covalent bond makes that
a new type of interaction possible: hydrogen bonding. For
instance, a water molecule consists of an oxygen atom
bonded to two hydrogen atoms. The unequal sharing of
electrons causes a distribution of partial charges on the
molecule. The oxygen of one water molecule monopolizes
the bonding electrons and acquires a partial negative
8 charge; as a result, this oxygen atom is attracted to
the partially positive hydrogen atoms of another water
molecule. This electrostatic attraction, 9 which is an
attraction referred to as intermolecular hydrogen bonding,
contributes to the surface tension that sustains the weight
of water striders and some other insects.
10 The presence of surface tension in water is just
one result of hydrogen bonding. From digestion to DNA
structure, this molecular force is integral 11 with many
life-sustaining processes. If atoms did not have different
values of electronegativity, hydrogen bonding would be
impossible—and life as we know it could not exist.
1 What principles dictate the relationships between
molecules? There are many factors at work, but these
interactions also depend indirectly on a principle known
as electronegativity. Although this is an atomic property,
it generates molecular 2 forces, that cause many of the
phenomena we observe every day.
3 Electronegativity, the measure of an atom’s affinity
for electrons, generally determines the type of bond
present between two atoms. A single bond between atoms
consists of two electrons. If the two atoms have similar
electronegativities, they share the two electrons equally
and form a nonpolar covalent bond. If two atoms have
significantly differing values of electronegativity, there are
two possible bond types: polar covalent and ionic. While
other factors also 4 corrupt the determination of bond
type, a difference in electronegativity between the values of
0.5 and 1.6 usually 5 result in a polar covalent bond, while
a difference of more than 2.0 usually results in an ionic
bond. In a polar covalent bond, the two bonding electrons
are shared 6 unequally, in an ionic bond: both electrons
are completely transferred to the more electronegative
atom. For example, the bond between oxygen (O) and
hydrogen (H) is classified as a polar covalent bond, because
they share the two bonding electrons unequally. This
polar bond type is partially caused by the difference in
electronegativities: 7 hydrogen has an electronegativity
of 2.20, while oxygen has an electronegativity of 3.44. When
the electronegativity of the hydrogen is subtracted from the
electronegativity of the oxygen, the difference is 1.24.
When a hydrogen atom is bonded to nitrogen, oxygen,
or fluorine, this particular polar covalent bond makes that
a new type of interaction possible: hydrogen bonding. For
instance, a water molecule consists of an oxygen atom
bonded to two hydrogen atoms. The unequal sharing of
electrons causes a distribution of partial charges on the
molecule. The oxygen of one water molecule monopolizes
the bonding electrons and acquires a partial negative
8 charge; as a result, this oxygen atom is attracted to
the partially positive hydrogen atoms of another water
molecule. This electrostatic attraction, 9 which is an
attraction referred to as intermolecular hydrogen bonding,
contributes to the surface tension that sustains the weight
of water striders and some other insects.
10 The presence of surface tension in water is just
one result of hydrogen bonding. From digestion to DNA
structure, this molecular force is integral 11 with many
life-sustaining processes. If atoms did not have different
values of electronegativity, hydrogen bonding would be
impossible—and life as we know it could not exist.