Group 14 B

Alkyne analogues have decreasing bond order down the group. C is a triple bond sp hybrid, Si/Ge/Sn are double bond sp² hybrids, and Pb forms single bonds with no hybridisation. The E-E distance increases down the group. The degree of bending also increases - alkynes are linear, Pb-Pb-R is at a 90 degree angle.

The decreasing willingness to hybridize is expressed in Bent's rule:

Atomic s character tends to concentrate in orbitals that are directed toward electropositive groups and atomic p character tends to concentrate in orbitals that are directed toward electronegative groups

Polarity when bonded to carbon increases down the group, which is associated with an increase in p character and a decrease in s character of the bonding orbitals.