Ionic Bonds (9.1.2)

Question 1

• Ionic compounds are composed of cations and anions present in ratios that
cause their charges to balance.

Answer 1

• Ionic compounds are composed of cations and anions present in ratios that
cause their charges to balance.

Question 2

• The Born-Haber cycle allows for the calculation of lattice energy, the energy
needed to break an ionic solid into its constituent gaseous ions.

Answer 2

• The Born-Haber cycle allows for the calculation of lattice energy, the energy
needed to break an ionic solid into its constituent gaseous ions.

Question 3

Ionic compounds are composed of cations and
anions joined by strong ionic bonds. An ionic bond
is a chemical bond formed when one atom
completely transfers one or more electrons to
another atom.
These cations and anions may be monatomic or
polyatomic.
The cations and anions are present in stoichiometric
ratios that cause the overall charges to balance.
Ionic compounds generally have strong bonds, are
hard crystals, and have high melting points.

Hess’s Law states that the enthalpy change (∆H)
for a multi-step process is equal to the sum of the
∆H values for the individual steps.
Lattice energy is the energy required to break an
ionic solid into its constituent gaseous ions.
Ionization energy (IE) is the energy required to
remove an electron from an atom, molecule or ion.
Electron affinity (EA) is the energy released when
an electron is added to a neutral atom.
The Born-Haber cycle, a special application of
Hess’s law, explains why sodium metal and chlorine
gas react to form the sodium chloride ionic lattice.
Steps of the Born-Haber cycle for NaCl:
1. Sublimation of the sodium metal.
2. Dissociation of the chlorine gas into
chlorine atoms.
3. Ionization of the sodium atoms to
sodium ions.
4. Ionization of the chlorine atoms to
chloride ions.
5. Condensation of the gaseous ions to
form an ionic lattice.

Answer 3

Ionic compounds are composed of cations and
anions joined by strong ionic bonds. An ionic bond
is a chemical bond formed when one atom
completely transfers one or more electrons to
another atom.
These cations and anions may be monatomic or
polyatomic.
The cations and anions are present in stoichiometric
ratios that cause the overall charges to balance.
Ionic compounds generally have strong bonds, are
hard crystals, and have high melting points.

Hess’s Law states that the enthalpy change (∆H)
for a multi-step process is equal to the sum of the
∆H values for the individual steps.
Lattice energy is the energy required to break an
ionic solid into its constituent gaseous ions.
Ionization energy (IE) is the energy required to
remove an electron from an atom, molecule or ion.
Electron affinity (EA) is the energy released when
an electron is added to a neutral atom.
The Born-Haber cycle, a special application of
Hess’s law, explains why sodium metal and chlorine
gas react to form the sodium chloride ionic lattice.
Steps of the Born-Haber cycle for NaCl:
1. Sublimation of the sodium metal.
2. Dissociation of the chlorine gas into
chlorine atoms.
3. Ionization of the sodium atoms to
sodium ions.
4. Ionization of the chlorine atoms to
chloride ions.
5. Condensation of the gaseous ions to
form an ionic lattice.

Question 4

Ionic compounds exist as crystalline solids in a
regular lattice of alternating cations and anions.
The Coulomb force changes with the square of the
charges involved. Notice that the lattice energy of
MgO is about four times greater than the lattice
energies of the other compounds. This increase in
lattice energy is because of the greater charges of
magnesium ion and oxide ion.

Answer 4

Ionic compounds exist as crystalline solids in a
regular lattice of alternating cations and anions.
The Coulomb force changes with the square of the
charges involved. Notice that the lattice energy of
MgO is about four times greater than the lattice
energies of the other compounds. This increase in
lattice energy is because of the greater charges of
magnesium ion and oxide ion.

Question 5

Which one of the following binary ionic compounds is expected to have the highest melting point?

Answer 5

MgS (D)

Question 6

Which of the following formulas accurately represents the binary ionic compound formed between magnesium and chlorine?

Answer 6

MgCl2 (C)

Question 7

Calculate the ΔH of formation for solid KCl given the following information:
K(s) → K(g)
ΔH = 64 kJ / mol (sublimation energy)
Cl2(g) → 2 Cl(g)
ΔH = 240 kJ / mol (Bond energy)
K(g) → K+ (g)
ΔH = 419 kJ / mol (Ionization energy)
Cl(g) → Cl − (g)
ΔH = −349 kJ / mol (Electron affinity)
KCl(s) → K+ (g) + Cl − (g)
ΔH = −690 kJ / mol (Lattice energy)

Answer 7

−436 kJ / mole (C)

Question 8

Which of the following formulas accurately represents the binary ionic compound formed between lithium and oxygen?

Answer 8

Li2O (B)

Question 9

Which one of the following binary ionic compounds is expected to have the lowest lattice energy?

Answer 9

LiCl (A)

Question 10

Which one of the following binary ionic compounds is expected to have the lowest lattice energy?

Answer 10

NaCl (A)

Question 11

Which one of the following binary ionic compounds is expected to have the highest lattice energy?

Answer 11

LiI (D)

In each ionic compound listed, the charges on the cation and anion are both ±1. In order to compare lattice energies of these compounds, it is necessary to consider the distance between ions that are bonded. The smaller the distance between ions, the greater the lattice energy is. Because each compound listed is an iodide, one must only consider the size of the cations listed. Lithium is the smallest cation of the list. Therefore, LiI should show the greatest lattice energy.

Question 12

True or false?

One would predict LiCl to have a higher melting point than MgCl2.

Answer 12

false (B)

Compare the lattice energies of MgCl2 and LiCl. Because LiCl has ions each with a charge of 1 and Mg has a charge of 2+, one would predict MgCl2 to have greater lattice energy and a greater melting point.

Question 13

Which of the following formulas accurately represents the binary ionic compound formed between magnesium and nitrogen?

Answer 13

Mg3N2 (C)

Magnesium must lose two electrons (becomes +2 ion) while nitrogen must gain three electrons (becomes-3 ion) in order to make eight valence electrons for each. In order that the number of electrons lost are equal to the number of electrons gained, three magnesium atoms (2 × 3 = 6 electrons) will react with two nitrogen atoms (3 × 2 = 6 electrons) to make Mg3N2.

Question 14

Which of the following formulas accurately represents the binary ionic compound formed between barium and oxygen?

Answer 14

BaO (D)

Barium has two valence electrons and oxygen has six valence electrons. In order for each to have eight valence electrons, barium must lose two electrons and oxygen must gain two electrons. This would dictate a 1:1 stoichiometry between the two.