The carbon–halogen bond series C–F, C–Cl, and C–Br provides an opportunity to connect electronegativity differences with percent ionic character.
Electronegativity values (Pauling scale):
C = 2.55 F = 3.98 Cl = 3.16 Br = 2.96
Consider a hypothetical set of gaseous molecules, each containing one carbon–halogen bond, under identical conditions.
(a) Calculate the electronegativity difference Δχ for each of the three bonds.
(b) Rank the three bonds from greatest to least percent ionic character, justifying your order on the basis of the Δχ values you calculated in part (a).
(c) Using Coulombic arguments, explain why an increase in Δχ is generally correlated with both shorter bond length and higher bond dissociation energy in carbon–halogen bonds.
(d) Suppose a fourth bond, C–I, were added to the series. Predict qualitatively where it would fall in the rankings from parts (b) and (c), and defend your prediction using periodic-trend reasoning.