Worksheet: Lattice Energies of Ionic Solids

In this worksheet, we will practice defining the lattice energy of an ionic solid and describing how its value varies with ion size and charge.

Q1:

The precious gemstone ruby is aluminum oxide, A l O 2 3 , containing traces of C r 3 + . The compound A l S e 2 3 is used in the fabrication of some semiconductor devices. Which has the larger lattice energy, A l O 2 3 or A l S e 2 3 , and why?

  • A A l S e 2 3 has the larger lattice enthalpy because selenium has more electrons than oxygen, creating stronger mutual attraction between ions in the lattice.
  • BWithout atomization, ionization and electron affinity data, it is impossible to predict the order of lattice enthalpies.
  • C A l S e 2 3 has the larger lattice enthalpy because the S e 2 ion is larger than the O 2 ion, so can interact with a greater number of A l 3 + ions.
  • DThe ionic charges in the two compounds are the same, so A l O 2 3 has the larger lattice enthalpy because O 2 is a smaller ion than S e 2 .
  • EThe ionic charges in the two compounds are the same, so A l O 2 3 has the larger lattice enthalpy because oxygen has a higher electron affinity than selenium.

Q2:

In which of the following sequences are compounds arranged in order of increasing lattice energy? Note that the B a 2 + ion is similar in radius to the K + ion and the S 2 ion is similar in radius to the C l ion.

  • A N a O 2 < K O 2 < K C l < K S 2 < B a S
  • B K C l < K O 2 < N a O 2 < B a S < K S 2
  • C B a S < K S 2 < K C l < K O 2 < N a O 2
  • D K C l < K S 2 < K O 2 < N a O 2 < B a S
  • E K S 2 < B a S < K O 2 < N a O 2 < K C l

Q3:

The lattice energy of L i F is 1 0 2 3 kJ/mol, and the L i F distance is 201 pm. M g O crystallizes in the same structure as L i F but with a M g O distance of 205 pm. Which of the following values most closely approximates the lattice energy of M g O ?

Q4:

Which of the following compounds requires the most energy to convert one mole of the solid into separate ions?

  • A K O 2
  • B K S 2
  • C C a S
  • D C a O
  • E C s S 2

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