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, AlO23, containing traces of Cr3+. The compound AlSe23 is used in the fabrication of some semiconductor devices. Which of AlO23 and AlSe23 has the larger lattice energy and why?

  • AThe ionic charges in the two compounds are the same, so AlO23 has the larger lattice enthalpy because O2 is a smaller ion than Se2.
  • B 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.
  • 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 Se2 ion is larger than the O2 ion and so can interact with a greater number of Al3+ ions.
  • EThe ionic charges in the two compounds are the same, so AlO23 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 Ba2+ ion is similar in radius to the K+ ion and the S2 ion is similar in radius to the Cl ion.

  • A K S 2 , B a S , K O 2 , N a O 2 , K C l
  • B K C l , K O 2 , N a O 2 , B a S , K S 2
  • C K C l , K S 2 , K O 2 , N a O 2 , B a S
  • 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

Q3:

The lattice energy of LiF is 1,023 kJ/mol, and the LiF distance is 201 pm. MgO crystallizes in the same structure as LiF but with a MgO distance of 205 pm. Which of the following values most closely approximates the lattice energy of MgO?

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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