Sigma hybrid orbitals

For each of the following molecules, determine what atomic orbitals on the central atom are allowed by symmetry to be used in the construction of sigma hybrid orbitals, a. NHj (trigonal pyramid) b. BF3 (trigonal plane) c. SF6 (octahedron) d. PF, (trigonal bipyramid)... 

For each of the following molecules, determine what atomic orbitals on the central atom are allowed by symmetry to be used in the construction of sigma hybrid orbitals. 

Fig. 11(c) shows the sigma-type interaction between a filled O2 tt-orbital and the empty d sp hybrid orbital on the iron atom. And Fig. 11(b) shows the 7T-type interaction between a filled c -orbital on the metal e.g.dyf) and one of the empty tt dioxygen orbitals. 

Figure 1.17 The hypothetical formation of the bonding molecular orbitals of ethane from two sp -hybridized carbon atoms and six hydrogen atoms. All of the bonds are sigma bonds. (Antibonding sigma molecular orbitals — are called a orbitals — are formed in each instance as well, but for simplicity these are not shown.)... 

Carbon atoms (1) and (4) use sp3 hybrid orbitals to form four sigma bonds, three by overlap with the hydrogen Is orbitals and one by overlap with an sp2 orbital from the central carbon (2). The two carbon atoms involved in the double bond undergo sp2 hybridization. They form C-H bonds by overlapping with Is orbitals of the H atoms. The C=C double bond is formed similarly to that described in (a). 

Sigma (o) bonds are formed by the end to end overlap of two orbitals. This overlap can take place between s orbitals, p orbitals or hybrid orbitals. 

Similarly, C — H sigma bonds in the C2H6 molecule are formed by the end to end overlap of sp3 hybrid orbitals of the carbon atoms with the Is orbitals of the hydrogen atoms. The C—Co bond is formed by the end to end overlap of the sp3 hybrid orbitals of the C atoms. So in the C2H6 molecule there are six C — H o bonds and one C—Co bond making seven o bonds in total. 

When carbon atoms undergo sp3 hybridization, the hybrid orbitals form sigma bonds. 

An important point to be stressed before we proceed further with our analysis concerns the formal correspondence, of hybrid orbitals and delocalized group orbitals. For example, consider the model system HN=NH which can exist in a cis or a tram geometry. We can understand whether sigma interactions favor one or the other geometry be means of one of the following two approaches ... 

In molecular orbital (MO) terminology, the MO formed by overlap between the carbon hybrid orbital and the metal hybrid orbital is called a sigma orbital. An atomic 3 orbital is perfectly spherical and hence has the highest possible symmetry. It has the same sign everywhere, by... 

NO 2, 0=N=0 . N has two cr bonds, no unshared pairs of electrons and therefore needs two hybrid orbitals. N uses sp hybrid orbitals and the cr bonds are linear. The geometry is controlled by the arrangement of the sigma bonds. 

Covalent bonds are formed when atomic orbitals overlap. The overlap of atomic orbitals is called hybridization, and the resulting atomic orbitals are called hybrid orbitals. There are two types of orbital overlap, which form sigma (cr) and pi (tt) bonds. Pi bonds never occur alone without the bonded atoms also being joined by a ct bond. Therefore, a double bond consists of a O bond and a tt bond, whereas a triple bond consists of a ct bond and two tt bonds. A sigma overlap occurs when there is one bonding interaction that results from the overlap of two s orbitals or an s orbital overlaps a p orbital or two p orbitals overlap head to head. A tt overlap occurs only when two bonding interactions result from the sideways overlap of two parallel p... 

Lone pair constitutes a hybrid orbital together with sigma bond(s). 

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