Chapter 8
A Chemical Bond: Forces that hold groups of atoms together and make them
function as a unit. A bond will form if the energy of the interaction of atoms
is lower than that of the separated atoms.
Types of chemical bonds:
1- Ionic Bonding: Result from the interaction of metals on the left side of the
periodic table with nonmetals on the right side (excluding the noble gases,
group 8A).
electrons are transferred
When sodium and chlorine react to form sodium chloride, electrons are
transferred from the sodium atoms to the chlorine atoms to form Na+ and Cl-
ions, which then aggregate to form solid sodium chloride.
Why does this happen?
The best simple answer is that the system can achieve the lowest possible
energy by behaving in this way.
The attraction of a chlorine atom for the extra electron and the very strong
mutual attractions of the oppositely charged ions provide the driving forces
for the process.
The resulting solid sodium chloride is a very sturdy material; it has a melting
point of approximately 800ᵒC. The bonding forces that produce this great
thermal stability result from the electrostatic attractions of the closely packed,
oppositely charged ions.
This is an example of ionic bonding. Ionic substances are formed when an
atom that loses electrons relatively easily reacts with an atom that has a high
affinity for electrons. That is, an ionic compound results when a metal reacts
with a nonmetal.
Tariq Bataineh
1
,The energy of interaction between a pair of ions can be calculated using
Coulomb’s law in the form:
where E has units of joules, r is the distance between the ion centers in
nanometers, and Q1 and Q2 are the numerical ion charges.
The negative sign indicates an attractive force. That is, the ion pair has lower
energy than the separated ions.
Coulomb’s law also can be used to calculate the repulsive energy when two
like charged ions are brought together. In this case the calculated value of the
energy will have a positive sign.
Tariq Bataineh
2
, Energy effects in Binary ionic compounds:
Lattice energy: the energy required to completely separate one mole of a solid
ionic compound into its gaseous ions.
The lattice energy is often defined as the energy released when an ionic
solid forms:
A measure of how much stabilization results from arranging oppositely
charged ions in an ionic solid is given by the lattice energy.
For Example: considering the formation of solid lithium fluoride from its
elements:
To see the energy terms associated with this process, we take advantage of
the fact that energy is a state function and break this reaction into steps, the
sum of which gives the overall reaction:
See next page
Tariq Bataineh
3
A Chemical Bond: Forces that hold groups of atoms together and make them
function as a unit. A bond will form if the energy of the interaction of atoms
is lower than that of the separated atoms.
Types of chemical bonds:
1- Ionic Bonding: Result from the interaction of metals on the left side of the
periodic table with nonmetals on the right side (excluding the noble gases,
group 8A).
electrons are transferred
When sodium and chlorine react to form sodium chloride, electrons are
transferred from the sodium atoms to the chlorine atoms to form Na+ and Cl-
ions, which then aggregate to form solid sodium chloride.
Why does this happen?
The best simple answer is that the system can achieve the lowest possible
energy by behaving in this way.
The attraction of a chlorine atom for the extra electron and the very strong
mutual attractions of the oppositely charged ions provide the driving forces
for the process.
The resulting solid sodium chloride is a very sturdy material; it has a melting
point of approximately 800ᵒC. The bonding forces that produce this great
thermal stability result from the electrostatic attractions of the closely packed,
oppositely charged ions.
This is an example of ionic bonding. Ionic substances are formed when an
atom that loses electrons relatively easily reacts with an atom that has a high
affinity for electrons. That is, an ionic compound results when a metal reacts
with a nonmetal.
Tariq Bataineh
1
,The energy of interaction between a pair of ions can be calculated using
Coulomb’s law in the form:
where E has units of joules, r is the distance between the ion centers in
nanometers, and Q1 and Q2 are the numerical ion charges.
The negative sign indicates an attractive force. That is, the ion pair has lower
energy than the separated ions.
Coulomb’s law also can be used to calculate the repulsive energy when two
like charged ions are brought together. In this case the calculated value of the
energy will have a positive sign.
Tariq Bataineh
2
, Energy effects in Binary ionic compounds:
Lattice energy: the energy required to completely separate one mole of a solid
ionic compound into its gaseous ions.
The lattice energy is often defined as the energy released when an ionic
solid forms:
A measure of how much stabilization results from arranging oppositely
charged ions in an ionic solid is given by the lattice energy.
For Example: considering the formation of solid lithium fluoride from its
elements:
To see the energy terms associated with this process, we take advantage of
the fact that energy is a state function and break this reaction into steps, the
sum of which gives the overall reaction:
See next page
Tariq Bataineh
3
