Lattice Energy
Properties affected by bond strength
• melting/boiling point (stronger bonds = higher
melting/boiling point)
Properties affected by bond strength
• melting/boiling point (stronger bonds = higher
melting point/boiling point)
• hardness (stronger bonds = harder crystals)
Properties affected by bond strength
• melting/boiling point (stronger bonds = higher
melting point/boiling point)
• hardness (stronger bonds = harder crystals)
• odor (stronger bonds = weaker odor)
Properties affected by bond strength
• melting/boiling point (stronger bonds = higher
melting point/boiling point)
• hardness (stronger bonds = harder crystals)
• odor (stronger bonds = weaker odor)
• state at room temperature (stronger bonds
are more likely to be solids)
Bond formation
• Whenever a new bond forms, energy is
released. The stronger the bond, the more
energy that is released.
Bond formation
• Whenever a new bond forms, energy is
released. The stronger the bond, the more
energy that is released.
• For ionic bonds, this energy is called lattice
energy.
Bond formation
• Whenever a new bond forms, energy is
released. The stronger the bond, the more
energy that is released.
• For ionic bonds, this energy is called lattice
energy.
• Higher lattice energy values correspond to
stronger bonds.
Bond formation
• Whenever a new bond forms, energy is
released. The stronger the bond, the more
energy that is released.
• For ionic bonds, this energy is called lattice
energy.
• Higher lattice energy values correspond to
stronger bonds.
• The amount of energy released when a bond
forms is identical to the amount of energy
required to break the bond.
Predicting lattice energy
• Two factors will determine the lattice energy
for ionic compounds.
Predicting lattice energy
• Two factors will determine the lattice energy
for ionic compounds.
– Bigger charges produce higher lattice energies (2+
and 2- produce stronger bonds than 1+ and 1-)
Predicting lattice energy
• Two factors will determine the lattice energy
for ionic compounds.
– Bigger charges produce higher lattice energies (2+
and 2- produce stronger bonds than 1+ and 1-)
– Fewer energy levels result in greater lattice
energies (LiF will have a greater lattice energy
than NaCl)
Predicting lattice energy
• Two factors will determine the lattice energy
for ionic compounds.
– Bigger charges produce higher lattice energies (2+
and 2- produce stronger bonds than 1+ and 1-)
– Fewer energy levels result in greater lattice
energies (LiF will have a greater lattice energy
than NaCl)
– Charge is by far the bigger factor and should
always be compared first!!!
Which compound will have the greatest lattice
energy, MgS or LiF?
Which compound will have the greatest lattice
energy, MgS or LiF?
• Magnitude of charge is the first thing we
should look at.
Which compound will have the greatest lattice
energy, MgS or LiF?
• Magnitude of charge is the first thing we
should look at.
– magnesium (2+ charge), sulfide (2- charge)
Which compound will have the greatest lattice
energy, MgS or LiF?
• Magnitude of charge is the first thing we
should look at.
– magnesium (2+ charge), sulfide (2- charge)
– lithium (1+ charge), fluoride (1- charge)
Which compound will have the greatest lattice
energy, MgS or LiF?
• Magnitude of charge is the first thing we
should look at.
– magnesium (2+ charge), sulfide (2- charge)
– lithium (1+ charge), fluoride (1- charge)
– MgS has the greater individual charges, so MgS
has the greater lattice energy.
Which compound will have a lower melting
point, Na2S or BeO?
Which compound will have a lower melting
point, Na2S or BeO?
• A lower melting point means we need to
select the compound with the lower lattice
energy. We check the charges first.
Which compound will have a lower melting
point, Na2S or BeO?
• A lower melting point means we need to
select the compound with the lower lattice
energy. We check the charges first.
– sodium (1+), sulfide (2-)
Which compound will have a lower melting
point, Na2S or BeO?
• A lower melting point means we need to
select the compound with the lower lattice
energy. We check the charges first.
– sodium (1+), sulfide (2-)
– beryllium (2+), oxide (2-)
Which compound will have a lower melting
point, Na2S or BeO?
• A lower melting point means we need to
select the compound with the lower lattice
energy. We check the charges first.
– sodium (1+), sulfide (2-)
– beryllium (2+), oxide (2-)
– sodium sulfide has smaller individual charges, so it
has the lower melting point.
Which compound has harder crystals, CaCl2 or
MgCl2?
Which compound has harder crystals, CaCl2 or
MgCl2?
• Harder crystals require a higher lattice energy.
First, check the charges.
Which compound has harder crystals, CaCl2 or
MgCl2?
• Harder crystals require a higher lattice energy.
First, check the charges.
– calcium (2+), chloride (1-)
Which compound has harder crystals, CaCl2 or
MgCl2?
• Harder crystals require a higher lattice energy.
First, check the charges.
– calcium (2+), chloride (1-)
– magnesium (2+), chloride (1-)
Which compound has harder crystals, CaCl2 or
MgCl2?
• Harder crystals require a higher lattice energy.
First, check the charges.
– calcium (2+), chloride (1-)
– magnesium (2+), chloride (1-)
– the charges are the same, so we need to see
which ions have fewer energy levels.
Which compound has harder crystals, CaCl2 or
MgCl2?
– the charges are the same, so we need to see
which ions have fewer energy levels.
– calcium (4), chloride (3)
Which compound has harder crystals, CaCl2 or
MgCl2?
– the charges are the same, so we need to see
which ions have fewer energy levels.
– calcium (4), chloride (3)
– magnesium (3), chloride (3)
Which compound has harder crystals, CaCl2 or
MgCl2?
– the charges are the same, so we need to see
which ions have fewer energy levels.
– calcium (4), chloride (3)
– magnesium (3), chloride (3)
– fewer energy levels give MgCl2 the higher lattice
energy and therefore, the harder crystals.
Which compound has the lower
boiling point, AgNO3 or K2SO4?
Which compound has the lower
boiling point, AgNO3 or K2SO4?
• Lower boiling point means a lower lattice
energy.
Which compound has the lower
boiling point, AgNO3 or K2SO4?
• Lower boiling point means a lower lattice
energy.
– silver (1+), nitrate (1-)
Which compound has the lower
boiling point, AgNO3 or K2SO4?
• Lower boiling point means a lower lattice
energy.
– silver (1+), nitrate (1-)
– potassium (1+), sulfate (2-)
Which compound has the lower
boiling point, AgNO3 or K2SO4?
• Lower boiling point means a lower lattice
energy.
– silver (1+), nitrate (1-)
– potassium (1+), sulfate (2-)
– Charges indicate a lower lattice energy for AgNO3.
Lower lattice energy means a lower boiling point.