Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
122 Chemistry: Matter and Change
Solving Problems: A Chemistry Handbook
SOLVING PROBLEMS:
A CHEMISTRY HANDBOOK
CHAPTER 12
12.2 Forces of Attraction
The attractive forces that hold particles together in ionic, covalent,
and metallic bonds are called intramolecular forces. Intermolecular
forces, which are weaker than intramolecular forces, also can hold
particles together. Three types of intermolecular forces are described
below: dispersion 1forces, dipole–dipole forces, and hydrogen
bonds.
Dispersion forces Weak forces that result from temporary shifts
in the density of electrons in electron clouds are called dispersion
forces, or London forces. When two nonpolar molecules are in close
contact, the electron cloud of one molecule repels the electron cloud
of the other molecule. As a result, the electron density in each electron cloud is greater in one region of the cloud. Two temporary
dipoles form. Weak dispersion forces exist between oppositely
charged regions of the dipoles. Dispersion forces, which are the
weakest intermolecular forces, are important only when no stronger
forces are acting on the particles. Dispersion forces are noticeable
between identical nonpolar molecules as the number of electrons
involved increases. For example, an increase in dispersion forces
explains why fluorine and chlorine are gases, bromine is a liquid,
and iodine is a solid at room temperature.
Dipole–dipole forces Attractions between oppositely charged
regions of polar molecules are called dipole–dipole forces. Polar
molecules have a permanent dipole and orient themselves so that
oppositely charged regions match up. Dipole–dipole forces are
stronger than dispersion forces as long as the molecules being compared are similar in mass.
Hydrogen bonds A hydrogen bond is a dipole–dipole attraction
that occurs between molecules containing a hydrogen atom bonded
to a small, highly electronegative atom with at least one lone electron pair. The hydrogen must be bonded to a fluorine, an oxygen, or
a nitrogen atom. Hydrogen bonds explain why water is a liquid at
room temperature, while compounds of comparable mass are gases.
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122 Chemistry: Matter and Change
Solving Problems: A Chemistry Handbook
SOLVING PROBLEMS:
A CHEMISTRY HANDBOOK
CHAPTER 12
12.2 Forces of Attraction
The attractive forces that hold particles together in ionic, covalent,
and metallic bonds are called intramolecular forces. Intermolecular
forces, which are weaker than intramolecular forces, also can hold
particles together. Three types of intermolecular forces are described
below: dispersion 1forces, dipole–dipole forces, and hydrogen
bonds.
Dispersion forces Weak forces that result from temporary shifts
in the density of electrons in electron clouds are called dispersion
forces, or London forces. When two nonpolar molecules are in close
contact, the electron cloud of one molecule repels the electron cloud
of the other molecule. As a result, the electron density in each electron cloud is greater in one region of the cloud. Two temporary
dipoles form. Weak dispersion forces exist between oppositely
charged regions of the dipoles. Dispersion forces, which are the
weakest intermolecular forces, are important only when no stronger
forces are acting on the particles. Dispersion forces are noticeable
between identical nonpolar molecules as the number of electrons
involved increases. For example, an increase in dispersion forces
explains why fluorine and chlorine are gases, bromine is a liquid,
and iodine is a solid at room temperature.
Dipole–dipole forces Attractions between oppositely charged
regions of polar molecules are called dipole–dipole forces. Polar
molecules have a permanent dipole and orient themselves so that
oppositely charged regions match up. Dipole–dipole forces are
stronger than dispersion forces as long as the molecules being compared are similar in mass.
Hydrogen bonds A hydrogen bond is a dipole–dipole attraction
that occurs between molecules containing a hydrogen atom bonded
to a small, highly electronegative atom with at least one lone electron pair. The hydrogen must be bonded to a fluorine, an oxygen, or
a nitrogen atom. Hydrogen bonds explain why water is a liquid at
room temperature, while compounds of comparable mass are gases.
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