8.2 sp Hybridization

C. sp hybridization

Hybrids derived from atomic s– and p orbitals

Digonal bonding: sp-hybrid orbitals

Returning to the example of BeH₂, we can compare the valence orbitals in the free atoms with those in the beryllium hydride molecule as shown here. Of course, the overlap between the hydrogen-1s orbitals and the two lobes of the beryllium sp-hybrid orbitals constitutes the two Be— H “bonds” in this molecule.

Notice that whereas a single p-orbital has lobes on both sides of the atom, a single sp-hybrid has most of its electron density on one side, with a minor and more spherical lobe on the other side. This minor lobe is centered on the central atom (some textbook illustrations don’t get this right.)

Figure 8.26 Formation of sp Hybrid Orbitals

As far as the shape of the molecule is concerned, the result is exactly the same as predicted by the VSEPR model (although hybrid orbital theory predicts the same result in a more fundamental way.) We can expect any central atom that uses sp-hybridization in bonding to exhibit linear geometry when incorporated into a molecule.

When two electron groups surround the central atom, we observe a linear shape

Both shape and orientation maximize overlap with the orbital of the other atom in the bond.

Figure 8.27 Orbital Overlap in sp Hybrid Orbitals

Figure 8.28 3D shape in sp Hybrid Orbitals

Beryllium chloride is one of examples of molecules where the central atom Be is sp hybridized.  The 2s and one of the three 2p orbitals of Be mix and form two sp orbitals. These overlap 3p orbitals of two Cl atoms of the four valence electrons-two from Be and one from each Cl-occupy the overlapped orbitals in pairs with opposite spins. The two unhybridized 2p orbitals of Be lie perpendicular to each other and to the bond axes. Thus through hybridization, the paired 2s electrons in the isolated Be atom are distributed into two sp orbitals, which form the two Be-Cl bond.

Cl                                 Be                    Cl

Figure 8.28 3D shape of sp Hybrid Orbitals in BeCl₂

Ref: Commons.wikimedia.org/

Figure 8.29 3D shape of sp Hybrid Orbitals in BeCl₂

Ref: Commons.wikimedia.org/

In case of acetylene(C₂H₂),each  carbon has two unhybridized p orbitals.

Figure 8.30 3D shape of sp Hybrid Orbitals in C

Ref: Commons.wikimedia.org

Figure 8.31 Formation of Pi Hybrid Orbitals in C

Ref: Commons.wikimedia.org

Figure 8.32 Electronic arrangement in different Hybrid Orbitals

Ref: Commons.wikimedia.org

 What you should be able to do

1. Make sure you thoroughly understand the following essential ideas which have been presented above.
2. Explain why the sharing of atomic orbitals (as implied in the Lewis model) cannot adequately account for the observed bonding patterns in simple molecules.
3. Sketch out a diagram illustrating how the plots of atomic s– and p– orbital wave functions give rise to a pair of hybrid orbitals.
4. Draw “orbital box” diagrams showing how combinations of an atomic s orbital and various numbers of p orbitals create sp, sp², and sp³ hybrid orbitals.
5. Show how hybrid orbitals are involved in the molecules methane, water, and ammonia.