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Worksheet: Molecular Bonds

In this worksheet, we will practice calculating the dissociation energies of different ionic, covalent, and van der Waals molecular bonds.

Q1:

The measured density of a C s I crystal is 4.51 g/cm3. Find the equilibrium separation distance of C s + and I – ions. Use a value of 259 g/mol for the molar mass of C s I .

Q2:

The electron affinity of Br is 2.18 eV and the ionization energy of Na is 5.14 eV. NaBr forms an ionic bond. At equilibrium separation, the atoms are 𝑟 = 0 . 2 5 0 0 n m apart.

Determine the electrostatic potential energy of the atoms.

Find the dissociation energy. Neglect the energy of repulsion.

Q3:

The characteristic energy of rotation for HCl is 1 . 3 3 × 1 0 − 3 eV, assuming a value of 35.4 u for the atomic mass of chlorine and 1.0 u for the atomic mass of hydrogen.

Determine the reduced mass μ for the HCl molecule.

  • A0.69 u
  • B0.32 u
  • C0.54 u
  • D0.97 u
  • E0.27 u

Find the separation distance between the H and Cl atoms.

Q4:

Determine the dissociation energy of 12.0 moles of sodium chloride (NaCl). Use a repulsion constant 𝑛 for NaCl of 8.00 and a Madelung constant of 1.75. The molar mass of NaCl is 58.44 g/mol and its density is 2.16 g/cm3. Coulomb’s constant is 8 . 9 9 × 1 0 9 N⋅m2/C2.

Q5:

What value of the repulsion constant, 𝑛 , gives the measured dissociation energy of 171 kcal/mol for KCl? The molar mass of KCl is 74.55 g/mol and its density is 1.98 g/cm3. Coulomb’s constant is 8 . 9 9 × 1 0 9 N⋅m2/C2.

Q6:

What value of the repulsion constant, 𝑛 , gives the measured dissociation energy of 188 kcal/mol for NaCl? Use a value of 1.75 for the Madelung constant and a value of 0.281 nm for the equilibrium separation of Na and Cl. Give your answer to two significant figures.

Q7:

Potassium fluoride ( K F ) is a molecule formed by an ionic bond. At equilibrium separation the atoms are 𝑟 = 0 . 2 5 5 0 n m apart. Determine the electrostatic potential energy of the atoms. The electron affinity of F is 3.40 eV and the ionization energy of K is 4.34 eV. Determine dissociation energy. (Neglect the energy of repulsion.)

Q8:

The measured density of a K B r crystal is 2.75 g/cm3. Find the equilibrium separation distance of K + and B r – ions. Use a value of 119.003 g/mol for the molar mass of K B r .

Q9:

Potassium chloride (KCl) is a molecule formed by an ionic bond. At equilibrium separation, the atoms are 𝑟 = 0 . 2 7 9 0 nm apart. Determine the electrostatic potential energy of the atoms given that coulomb’s constant is 8 . 9 9 × 1 0 9 N⋅m2/C2. Give your answer in electron-volts (eV).

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