Elements X, Y and Z have electronegativities of 1.0, 2.5 and 3.0 respectively. Three binary compounds are formed: XY, XZ and YZ.

(i) Using the rule that a bond is ionic when the electronegativity difference $\Delta EN \ge 1.7$ and covalent otherwise, state the type of bond (ionic or covalent) in each compound.

(ii) For an ionic bond, the lattice energy (in kJ mol$^{-1}$) can be estimated as $U = 500 \times \Delta EN$. For a covalent bond, the bond enthalpy (in kJ mol$^{-1}$) is approximated by $E = 350 - 20\Delta EN$.

Calculate the estimated bond energy for each compound and rank the three compounds from highest to lowest bond energy.

Question

Elements X, Y and Z have electronegativities of 1.0, 2.5 and 3.0 respectively. Three binary compounds are formed: XY, XZ and YZ.

(i) Using the rule that a bond is ionic when the electronegativity difference $\Delta EN \ge 1.7$ and covalent otherwise, state the type of bond (ionic or covalent) in each compound.

(ii) For an ionic bond, the lattice energy (in kJ mol$^{-1}$) can be estimated as $U = 500 \times \Delta EN$. For a covalent bond, the bond enthalpy (in kJ mol$^{-1}$) is approximated by $E = 350 - 20\Delta EN$.

Calculate the estimated bond energy for each compound and rank the three compounds from highest to lowest bond energy.

Accepted Answer

XZ is ionic, XY and YZ are covalent; ranking by bond energy: XZ > YZ > XY

Igcse Model Questions Vol1 2023 Chemistry Question 1

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