After completing this section, you should be able to apply the concept of hybridization of atoms such as N, O, P and S to explain the structures of simple species containing these atoms.
Make certain that you can define, and use in context, the key term below.
- lone pair electrons
Nitrogen is frequently found in organic compounds. As with carbon atoms, nitrogen atoms can be sp3-, sp2- or sp‑hybridized.
Note that, in this course, the term “lone pair” is used to describe an unshared pair of electrons.
The valence-bond concept of orbital hybridization can be extrapolated to other atoms including nitrogen, oxygen, phosphorus, and sulfur. In other compounds, covalent bonds that are formed can be described using hybrid orbitals.
The nitrogen is sp3 hybridized which means that it has four sp3 hybrid orbitals. Two of the sp3 hybridized orbitals overlap with s orbitals from hydrogens to form the two N-H sigma bonds. One of the sp3 hybridized orbitals overlap with an sp3 hybridized orbital from carbon to form the C-N sigma bond. The lone pair electrons on the nitrogen are contained in the last sp3 hybridized orbital. Due to the sp3 hybridization the nitrogen has a tetrahedral geometry. However, the H-N-H and H-N-C bonds angles are less than the typical 109.5o due to compression by the lone pair electrons.
The oxygen is sp3 hybridized which means that it has four sp3 hybrid orbitals. One of the sp3 hybridized orbitals overlap with s orbitals from a hydrogen to form the O-H sigma bonds. One of the sp3 hybridized orbitals overlap with an sp3 hybridized orbital from carbon to form the C-O sigma bond. Both the sets of lone pair electrons on the oxygen are contained in the remaining sp3 hybridized orbital. Due to the sp3 hybridization the oxygen has a tetrahedral geometry. However, the H-O-C bond angles are less than the typical 109.5o due to compression by the lone pair electrons.
Phosphorus can have have expanded octets because it is in the n = 3 row. Typically, phosphorus forms five covalent bonds. In biological molecules, phosphorus is usually found in organophosphates. Organophosphates are made up of a phosphorus atom bonded to four oxygens, with one of the oxygens also bonded to a carbon. In methyl phosphate, the phosphorus is sp3 hybridized and the O-P-O bond angle varies from 110 ° to 112o.
Methanethiol & Dimethyl Sulfide
In biological system, sulfur is typically found in molecules called thiols or sulfides. In a thiol, the sulfur atom is bonded to one hydrogen and one carbon and is analogous to an alcohol O-H bond. In a sulfide, the sulfur is bonded to two carbons. In both cases the sulfur is sp3 hybridized and the bond angles are much less than the typical 109.5o.
Identify geometry and lone pairs on each heteroatom of the molecules given.
Diethyl ether would have two lone pairs of electrons and would have a bent geometry around the oxygen.
Dimethyl amine would have one lone pair and would show a pyramidal geometry around the nitrogen.