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Lesson: Lattice Energies of Ionic Solids

Worksheet • 4 Questions

Q1:

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 ?

Q2:

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?

  • AThe 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 .
  • BThe 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.
  • CWithout atomization, ionization and electron affinity data, it is impossible to predict the order of lattice enthalpies.
  • D 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.
  • E 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.

Q3:

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

Q4:

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

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