9.1.2 Ionic Bonds

Question 1

Ionic Bonds

Answer 1

• Ionic compounds are composed of cations and anions present in ratios that cause their charges to balance.
• 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 2

note

Answer 2

• 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 (ΔH) for a
  multi-step process is equal to the sum of the ΔH 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.
• 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 3

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

Answer 3

LiI

Question 4

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

Answer 4

Li2O

Question 5

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

Answer 5

MgS

Question 6

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

Answer 6

LiCl

Question 7

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

Answer 7

MgCl2

Question 8

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

Answer 8

Mg3N2

Question 9

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

Answer 9

NaCl

Question 10

True or false?

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

Answer 10

false

Question 11

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

Answer 11

BaO

Question 12

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 12

−436 kJ / mole