Four gas-phase diatomic molecules are listed below together with their bond lengths and the Pauling electronegativity values of the constituent atoms.
• CO bond length = 113pmχ(C)=2.5, χ(O)=3.5
• NO bond length = 115pmχ(N)=3.0, χ(O)=3.5
• HF bond length = 92pmχ(H)=2.1, χ(F)=4.0
• NaCl bond length = 236pmχ(Na)=0.9, χ(Cl)=3.0
Assume that a larger difference in electronegativity generally leads to a larger percent ionic character, but that the continuum of bonding requires consideration of additional factors beyond Δχ alone.
(a) Rank the four bonds from least to greatest expected percent ionic character. Clearly state any criteria you use in establishing the order.
(b) Identify the bond that is most likely to exhibit the largest bond dipole moment and justify your choice with reference to both electronegativity and bond length.
(c) Despite having similar Δχ values, the CO and NO bonds possess measurably different dipole moments. Describe two factors—other than Δχ—that can account for differences in ionic character between bonds with comparable electronegativity differences.
(d) For one of the bonds you ranked, explain how its placement on the covalent–ionic continuum would influence its expected solid-state electrical conductivity if a macroscopic sample of the pure substance were formed.