Lattice Energy. Properties affected by bond strength melting/boiling point (stronger bonds = higher melting/boiling point)

Lattice Energy

Properties affected by bond strength

• melting/boiling point (stronger bonds = higher melting/boiling point)


• melting/boiling point (stronger bonds = higher melting point/boiling point)

• hardness (stronger bonds = harder crystals)



• hardness (stronger bonds = harder crystals)• odor (stronger bonds = weaker odor)



• 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


• For ionic bonds, this energy is called lattice energy.

Bond formation



• 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.


• 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.


• 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-)



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)



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?


• Magnitude of charge is the first thing we should look at.


• Magnitude of charge is the first thing we should look at.– magnesium (2+ charge), sulfide (2- charge)


• Magnitude of charge is the first thing we should look at.– magnesium (2+ charge), sulfide (2- charge) – lithium (1+ charge), fluoride (1- charge)


• 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?


• A lower melting point means we need to select the compound with the lower lattice energy. We check the charges first.


• 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-)


• 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-)


• 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?


• Harder crystals require a higher lattice energy. First, check the charges.


• Harder crystals require a higher lattice energy. First, check the charges.– calcium (2+), chloride (1-)


• Harder crystals require a higher lattice energy. First, check the charges.– calcium (2+), chloride (1-)– magnesium (2+), chloride (1-)


• 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.


– the charges are the same, so we need to see which ions have fewer energy levels.

– calcium (4), chloride (3)



– calcium (4), chloride (3)– magnesium (3), chloride (3)



– 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?


• Lower boiling point means a lower lattice energy.


• Lower boiling point means a lower lattice energy.– silver (1+), nitrate (1-)


• Lower boiling point means a lower lattice energy.– silver (1+), nitrate (1-)– potassium (1+), sulfate (2-)


• 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.

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Lattice Energy. Properties affected by bond strength melting/boiling point (stronger bonds = higher melting/boiling point)