The principles of chemical bonding in hetenuclear diatomics or any other class of molecules are the same as those of the homonuclear diatomics studied in the earlier Lecture (lecture 7). Some differences naturally appear in hetenuclear diatomics (as compared to the homonuclear diatomics) such as the loss of symmetry, since the two participating nuclei are different. The plane perpendicular to, and bisecting the internuclear axis is not a plane of symmetry in hetenuclear diatomics.
As the nuclear charges and the atomic electron densities on the two participating atoms are different, the abilities of the two atoms to draw electron clouds towards themselves are different. The overall charge density in the molecule will be drawn towards the atom which has a greater value of electron negativity (the ability of an atom to draw electrons towards itself).The molecular orbitals will also lack the reflection symmetry (with respect to the perpendicular plane mentioned above) and the inversion symmetry (with respect to, or across the center of the molecule) present in the MOs of homonuclear diatomics will be absent in hetenuclear diatomics.
Furthermore, the energy levels of two orbitals trying to overlap and form a bond are different and the overlap is often not effective whenever the energy levels are very different. Atoms, therefore adopt new strategies so that the modified (or "new") energy levels of the two participating orbitals (of the two atoms) are much closer to one another. We will illustrate this principle, referred to as hybridization (which you would have already come across in molecules such as CH4, C2H4 and C2H2) in the molecule CO.
The nuclear charges now refer to the individual nuclear charges (generally distinct). The molecular orbitals are once again written as
(8.1)
The values of ci are now not all the same/similar to the values they had in the homonuclear cases, but are determined by the nuclear charge, electron negativity and so on. Larger the value of ci, greater the contribution of the corresponding AO, in the molecular orbital. Actually
gives the probability density of the MO and if
is normalized gives a measure of the extent of the contribution of the AO in the MO. We shall now consider the sketches of the contours of the MOs of a hetenuclear diatomic.
in the molecular orbital. Actually
gives the probability density of the MO and if
is normalized 
gives a measure of the extent of the contribution of the AO in the MO. We shall now consider the sketches of the contours of the MOs of a hetenuclear diatomic. 
