Orbitals for Incomplete s-p Shells

The formation of a fourth bond by boron would strengthen the bonds (all bond orbitals becoming tetrahedral) and stabilize the molecule we can thus understand the ability of boron trimethyl to add ammonia to 

Their bond strength is 1.991, only slightly less than that of tetrahedral orbitals. 14 H. A. L5vy and L. O. Brockway, J.A.C.S. 59, 2085 (1937). 

In a molecule such as mercury dimethyl the two bond orbitals would be expected to use all the orbital between them.17 The simple treatment shows that the two bonds would then be opposed. This is substantiated by the observation of a linear configuration for gas mole- 

17 The two corresponding bond orbitals (with bond directions taken along the z axis) are 

The description of the bond orbitals of the carbon atom as sp8 tetrahedral hybrid orbitals is satisfactory in many respects, but it can be improved. One improvement is that of concentrating the orbitals more closely about the bond direction by the introduction of some d and/character.21 

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