Polar and non-polar E-H bonds

Although we refer to compounds of the type EHn (E = any element) as hydrides, and this tends to suggest the presence of H^- (or at least, H^δ- ), the difference in electronegativity values between E and H means that the E_H bond may be non-polar, or polar in either of the senses shown in Figure 9.4. For H, χ^P = 2.2 and a number of E^_H bonds in which E is a p-block element (e.g. B^_H, C^_H, Si^_H,P^_H) are essentially non-polar. Since metals are electropositive, the H atom in an M^_H bond carries a δ^- partial charge. In contrast, N, O and F are more electronegative than H, and in N^_H, O^_H and F^_H bonds, the H atom carries a δ^-‏ partial charge. The molecular environment of an E^_H bond also influences the magnitude of the bond dipole and properties associated with the bond. This is demonstrated by a comparison of the pKa values for CH₃CO₂H (pKa  = 4.75) and CF₃CO₂H (pKa = 0.23).