8.2 sp2 Hybridization
B. Sp2 Hybridization:
From an energy standpoint, we can represent the transition from atomic s– and p-orbitals to an sp hybrid orbital in this way:
Figure 8.17 Atomic Orbital overlap in sp2 Hybridization
Notice here that 1) the total number of occupied orbitals is conserved,
and 2) the two sp hybrid orbitals are intermediate in energy between their parent atomic orbitals.
In terms of plots of the actual orbital functions ψ we can represent the process as follows:
Figure 8.18 Atomic Orbital overlap in sp Hybridization
The probability of finding the electron at any location is given not by ψ, but by ψ2, whose form is roughly conveyed by the solid figures in this illustration.
In order to rationalize the trigonal planar electron-group arrangement and the shape of the molecules based on hybridization
Figure 8.19 Formation of sp2 hybrid Orbital
When one s-orbital mixes with two out three p-orbitals, three sp2 hybrid orbitals are produced and one p orbital remains un-hybridized.
Figure 8.20 3D Arrangement of hybrid Orbitals
Figure 8.21 Shape of hybrid Orbitals
Example: BF3
VB Theory proposes that the central B atom in BF3 molecule is sp2 hybridized. The figure below shows three sp2 hybrid orbitals in the trigonal plane, with the 3rd 2p orbital unhybridized and perpendicular to the plane. Each sp2 hybrid orbital overlaps with 2p orbital of F atom. There are total six valence electrons are present in three sp2 orbitals, 3 from B atom and one from each F atom.
Figure 8.22 3D Shape of hybrid Orbitals in BF3
Ethylene(C2H4) is the example of a molecule where Sp2 hybridization can be observed. Look at the diagram below. VB theory can explain the double nature of the carbon carbon bond in ethylene. Each C atom’s four valence electrons half fill its three sp2 orbitals and its unhybridized p orbitals, which lied perpendicular to the sp2 plane. Two sp2 orbitals from each C forms C-H sigma bond by overlapping 1s orbital of H atom.
Figure 8.23 sp2 Hybrid Orbitals overlap in C2H4
The third sp2 orbital forms a C-C sigma bond with another C because their orientation allows end-to-end overlap. With the σ-bonded C atoms near each other, their half-filled un-hybridized 2p orbitals are close enough to overlap side by side. Such overlap forms п bonds.
Figure 8.24 Electron Cloud in C2H4
Pi bonds and sp2 hybridized orbitals | Structure and bonding | Organic chemistry | Khan Academy
Trigonal (sp2) hybridization
We can now go on to apply the same ideas to some other simple molecules. In boron trifluoride, for example, we start with the boron atom, which has three outer-shell electrons in its normal or ground state, and three fluorine atoms, each with seven outer electrons. As is shown in this configuration diagram, one of the three boron electrons is unpaired in the ground state. In order to explain the trivalent bonding of boron, we postulate that the atomic s– and p– orbitals in the outer shell of boron mix to form three equivalent hybrid orbitals. These particular orbitals are called sp2 hybrids, meaning that this set of orbitals is derived from one s- orbital and two p-orbitals of the free atom.
Figure 8.25 Electronic Arrangement in sp2 hybrid orbitals in BF3
This illustration shows how an s-orbital mixes with two p orbitals to form a set of three sp2 hybrid orbitals. Notice again how the three atomic orbitals yield the same number of hybrid orbitals.
Boron trifluoride BF3 is a common example of sp2 hybridization. The molecule has plane trigonal geometry.
Figure 8.25 3D shape in sp2 hybrid orbitals in BF3