In what type of orbital does the lone pair on each N atom reside
The correct answer and explanation is:
The lone pair on each nitrogen (N) atom in a molecule typically resides in an sp³ hybrid orbital. Nitrogen, which is in Group 15 of the periodic table, has five valence electrons. In molecules like ammonia (NH₃), nitrogen forms three sigma bonds with hydrogen atoms. The fourth electron remains in an orbital that is not involved in bonding, forming a lone pair. This lone pair occupies an sp³ hybrid orbital.
To understand why nitrogen uses an sp³ orbital, it’s important to recognize its electronic configuration. The nitrogen atom in its ground state has an electron configuration of 1s² 2s² 2p³. When nitrogen forms a molecule like NH₃, one of the 2s electrons is promoted to the empty 2p orbital. This results in an excited state where nitrogen has three unpaired electrons available for bonding.
In a molecule, nitrogen’s 2s and three 2p orbitals hybridize to form four equivalent sp³ hybrid orbitals. Three of these sp³ orbitals overlap with the hydrogen 1s orbitals to form bonds, while the fourth sp³ orbital holds the lone pair of electrons.
The lone pair affects the geometry of the molecule. In ammonia, the molecule adopts a trigonal pyramidal shape because the lone pair occupies one of the sp³ hybrid orbitals, pushing the hydrogen atoms closer together. The lone pair itself is in an sp³ orbital, and it exerts a repulsive force on the bonding pairs, which slightly compresses the bond angles from the ideal 109.5 degrees of a perfect tetrahedron.
Thus, in summary, the lone pair on each nitrogen atom typically resides in an sp³ hybrid orbital, and the type of orbital plays a crucial role in determining the molecule’s geometry and reactivity.