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Solving Problems: A Chemistry Handbook
Chemistry: Matter and Change
73
SOLVING PROBLEMS:
A CHEMISTRY HANDBOOK
CHAPTER 8
c. HCN, in which C is the central atom, two electrons are
shared by H and C, and six electrons are shared by C and N
d. CO 2 , in which C is the central atom, four electrons are
shared by C and the first O, and four electrons are shared by
C and the second O
Bond length and strength The distance between the nuclei of
two bonded atoms is called bond length. When the balance of forces
between the atoms is sufficiently upset, the bond can break. Energy
is absorbed when a bond breaks and is released when a bond forms.
The amount of energy required to break a covalent bond is called the
bond dissociation energy and always has a positive value. The
stronger the bond, the greater is the bond dissociation energy, and,
therefore, the more difficult it is to break the bond. For similar-sized
atoms, it is typically the case that a shorter bond has a greater bond
dissociation energy than does a longer bond. Triple bonds are usually shorter and have greater bond dissociation energies than do
double bonds. Double bonds are usually shorter and have greater
bond dissociation energies than do single bonds.
The total energy change in a chemical reaction is determined
from the energy of the bonds broken and formed. In an endothermic
reaction, more energy is required to break existing bonds in the reactants than is released when the new product bonds form. In an
exothermic reaction, more energy is released in the formation of the
new product bonds than is required to break bonds in the reactants.
Practice Problems
3. The bond length between two double-bonded nitrogen atoms
within a molecule of a certain compound is less than that
between two single-bonded carbon atoms within another molecule. Given that N and C are next to each other in the periodic
table, how would you expect the bond dissociation energies and
bond strengths of these two bonds to compare?
4. A molecule of ethene (C 2 H 4 ) contains a double bond between
the two carbon atoms. A molecule of ethyne (C 2 H 4 ) contains a
triple bond between the two carbon atoms. How would you
expect the lengths, strengths, and dissociation energies of these
two bonds to compare?
▲
Solving Problems: A Chemistry Handbook
Chemistry: Matter and Change
73
SOLVING PROBLEMS:
A CHEMISTRY HANDBOOK
CHAPTER 8
c. HCN, in which C is the central atom, two electrons are
shared by H and C, and six electrons are shared by C and N
d. CO 2 , in which C is the central atom, four electrons are
shared by C and the first O, and four electrons are shared by
C and the second O
Bond length and strength The distance between the nuclei of
two bonded atoms is called bond length. When the balance of forces
between the atoms is sufficiently upset, the bond can break. Energy
is absorbed when a bond breaks and is released when a bond forms.
The amount of energy required to break a covalent bond is called the
bond dissociation energy and always has a positive value. The
stronger the bond, the greater is the bond dissociation energy, and,
therefore, the more difficult it is to break the bond. For similar-sized
atoms, it is typically the case that a shorter bond has a greater bond
dissociation energy than does a longer bond. Triple bonds are usually shorter and have greater bond dissociation energies than do
double bonds. Double bonds are usually shorter and have greater
bond dissociation energies than do single bonds.
The total energy change in a chemical reaction is determined
from the energy of the bonds broken and formed. In an endothermic
reaction, more energy is required to break existing bonds in the reactants than is released when the new product bonds form. In an
exothermic reaction, more energy is released in the formation of the
new product bonds than is required to break bonds in the reactants.
Practice Problems
3. The bond length between two double-bonded nitrogen atoms
within a molecule of a certain compound is less than that
between two single-bonded carbon atoms within another molecule. Given that N and C are next to each other in the periodic
table, how would you expect the bond dissociation energies and
bond strengths of these two bonds to compare?
4. A molecule of ethene (C 2 H 4 ) contains a double bond between
the two carbon atoms. A molecule of ethyne (C 2 H 4 ) contains a
triple bond between the two carbon atoms. How would you
expect the lengths, strengths, and dissociation energies of these
two bonds to compare?
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