Bonding in NH₃

The nitrogen in NH₃ has five valence electrons. After hybridization these five electrons are placed in the four equivalent sp³ hybrid orbitals. The electron configuration of nitrogen now has one sp³ hybrid orbital completely filled with two electrons and three sp³ hybrid orbitals with one unpaired electron each. The two electrons in the filled sp³ hybrid orbital are considered non-bonding because they are already paired. These electrons will be represented as a lone pair on the structure of NH₃. The three unpaired electrons in the hybrid orbitals are considered bonding and will overlap with the s orbitals in hydrogen to form N-H sigma bonds. Note! This bonding configuration was predicted by the Lewis structure of NH₃.

The four sp³ hybrid orbitals of nitrogen orientate themselves to form a tetrahedral geometry. The three N-H sigma bonds of NH₃ are formed by sp³(N)-1s(H) orbital overlap. The fourth sp³ hybrid orbital contains the two electrons of the lone pair and is not directly involved in bonding.

Methyl amine

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 109.5^o due to compression by the lone pair electrons.

Bonding in H₂O

The oxygen in H₂O has six valence electrons. After hybridization these six electrons are placed in the four equivalent sp³ hybrid orbitals. The electron configuration of oxygen now has two sp³ hybrid orbitals completely filled with two electrons and two sp³ hybrid orbitals with one unpaired electron each. The filled sp³ hybrid orbitals are considered non-bonding because they are already paired. These electrons will be represented as a two sets of lone pair on the structure of H₂O . The two unpaired electrons in the hybrid orbitals are considered bonding and will overlap with the s orbitals in hydrogen to form O-H sigma bonds. Note! This bonding configuration was predicted by the Lewis structure of H₂O.

The four sp³ hybrid orbitals of oxygen orientate themselves to form a tetrahedral geometry. The two O-H sigma bonds of H₂O are formed by sp³(O)-1s(H) orbital overlap. The two remaining sp³ hybrid orbitals each contain two electrons in the form of a lone pair.

Methanol

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 109.5^o due to compression by the lone pair electrons.

Methyl phosphate

The bond pattern of phosphorus is analogous to nitrogen because they are both in period 15. However, 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 112^o.

Methanethiol & Dimethyl Sulfide

Sulfur has a bonding pattern similar to oxygen because they are both in period 16 of the periodic table. Because sulfur is positioned in the third row of the periodic table it has the ability to form an expanded octet and the ability to form more than the typical number of covalent bonds. 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. The simplest example of a thiol is methane thiol (CH₃SH) and the simplest example of a sulfide is dimethyl sulfide [(CH₃)₃S]. In both cases the sulfur is sp³ hybridized, however the sulfur bond angles are much less than the typical tetrahedral 109.5^o being 96.6^o and 99.1^o respectively.

methanethiol

dimethyl sulfide

1.10 Exercises