Chapter 1.10, Problem 14P

Interpretation Introduction

a) The oxygen atom in dimethyl ether, CH₃-O-CH₃

Interpretation:

The number of nonbonding lone pair of electrons present on oxygen atom in dimethyl ether is to be identified. Further its expected geometry is to be stated.

Concept introduction:

The electrons present in the valence shell of an atom that are not involved in bonding with other atoms are called nonbonding or lone pair of electrons. In a molecule, if an atom has only single electrons in all hybridized orbitals then the bonds formed by these orbitals will be equivalent in all respects. The molecule will thus have a regular structure. But if the atom contains single electron as well as unshared pairs of electrons in the hybridized orbitals, the orbitals with unshared pair of electrons will tend to occupy as much space as those orbitals involved in bonding. The bond angles will be slightly different from the expected bond angle and hence the molecule will not have a regular geometry.

To determine:

The number of nonbonding lone pair of electrons present on oxygen atom in dimethyl ether and its expected geometry.

Interpretation Introduction

b) The nitrogen atom in trimethylamine, CH₃-N- [CH₃]₂

Interpretation:

The number of nonbonding lone pair of electrons present on nitrogen atom in trimethylamine, is to be identified. Further its expected geometry is to be stated.

Concept introduction:

The electrons present in the valence shell of an atom that are not involved in bonding with other atoms are called nonbonding or lone pair of electrons. In a molecule, if an atom has only single electrons in all hybridized orbitals then the bonds formed by these orbitals will be equivalent in all respects. The molecule will thus have a regular structure. But if the atom contains single electron as well as unshared pairs of electrons in the hybridized orbitals, the orbitals with unshared pair of electrons will tend to occupy as much space as those orbitals involved in bonding. The bond angles will be slightly different from the expected bond angle and hence the molecule will not have a regular geometry.

To determine:

The number of nonbonding lone pair of electrons present on nitrogen atom in trimethylamine and its expected geometry.

Interpretation Introduction

c) The phosphorus atom in phosphine, PH₃

Interpretation:

The number of nonbonding lone pair of electrons present on phosphorus atom in phosphine is to be identified. Further the expected geometry of phosphorus atom in phosphine is to be stated.

Concept introduction:

The electrons present in the valence shell of an atom that are not involved in bonding with other atoms are called nonbonding or lone pair of electrons. In a molecule, if an atom has only single electrons in all hybridized orbitals then the bonds formed by these orbitals will be equivalent in all respects. The molecule will thus have a regular structure. But if the atom contains single electron as well as unshared pairs of electrons in the hybridized orbitals, the orbitals with unshared pair of electrons will tend to occupy as much space as those orbitals involved in bonding. The bond angles will be slightly different from the expected bond angle and hence the geometry of the molecule will be pyramidal.

To determine:

The number of nonbonding lone pair of electrons present on phosphorus atom in phosphine and its expected geometry.

Answer:

The phosphorus atom in phosphine has one lone pair of electrons. The phosphorus atom is in sp³ hybridized state with one orbital occupied by lone pairs of electrons. Hence the geometry will be pyramid.

Explanation:

Phosphorus atom has five electrons in its valence shell. It has formed three single bonds with three hydrogen atoms in phosphine. Therefore one lone pair of electrons remains on phosphorus atom. In phosphine the phosphorus atom is in sp³ hybridized state. Three of the sp³ hybrid orbitals containing single electron are utilized for forming three P-H sigma bonds. The fourth sp³ hybrid orbital accommodates the lone pair of electrons and it occupy as much space as a P-H bond does. The H-P-H bond angles deviate slightly from the normal tetrahedral angle. Hence the shape is pyramidal.

Conclusion:

The phosphorus atom in phosphine has one lone pair of electrons. The phosphorus atom is in sp³ hybridized state with one orbital occupied by lone pairs of electrons. Hence the structure will be pyramidal.

Interpretation Introduction

d) The sulfur atom in the amino acid methionine

Interpretation:

The number of nonbonding lone pair of electrons present on sulfur atom in the amino acid methionine is to be identified and to state its expected geometry.

Concept introduction:

The electrons present in the valence shell of an atom that are not involved in bonding with other atoms are called nonbonding or lone pair of electrons. In a molecule, if an atom has only single electrons in all hybridized orbitals then the bonds formed by these orbitals will be equivalent in all respects. The molecule will thus have a regular structure. But if the atom contains single electron as well as unshared pairs of electrons in the hybridized orbitals, the orbitals with unshared pair of electrons will tend to occupy as much space as those orbitals involved in bonding. The bond angles will be slightly different from the expected bond angle.

To determine:

The number of nonbonding lone pair of electrons present on sulfur atom in the amino acid methionine and its expected geometry.