Chapter MS, Problem 2PQ

Interpretation Introduction

Interpretation:

The structure of the molecule of type ${\text{ML}}_{\text{4}}$ that has four single bonds and no lone pairs has to be determined.

Concept Introduction:

VSEPR or valence shell electron pair repulsion theory predicts the shape of the molecules with the use of arrangement of electrons around the central metal atom. Its postulates are as follows:

1. The shape of the molecules is governed by the repulsion between electron pairs situated in the outermost or valence shell of the atoms.

2. A distortion is observed in the shape of the molecules if lone pairs are present in it. These are the electron pairs that do not participate in the chemical bonding between the atoms. The electron pairs that take part in bond formation are known as bond pairs.

3. The order of repulsion of electron pairs is as follows:

  $\text{lp}-\text{lp repulsion}>\text{lp}-\text{bp repulsion }>\text{bp}-\text{bp repulsion}$

4. Multiple bonds create more repulsion as compared to single bonds.

5. The following table shows the various molecular shapes that match to different number of electron pairs:

$\begin{array}{ccc}\begin{array}{l}\text{Number of}\\ \text{electron groups}\end{array}& \begin{array}{l}\text{Number of }\\ \text{lone pairs}\end{array}& \text{Molecular geometry}\\ 2& 0& \text{Linear}\\ 3& 0& \text{Trigonal planar}\\ 3& 1& \text{Bent}\\ 4& 0& \text{Tetrahedral}\\ 4& 1& \text{Trigonal pyramid}\\ 4& 2& \text{Bent}\\ 5& 0& \text{Trigonal bipyramidal}\\ 5& 1& \text{See}-\text{saw}\\ 5& 2& \text{T}-\text{structure}\\ 5& 3& \text{Linear}\\ 6& 0& \text{Octahedral}\\ 6& 1& \text{Square pyramidal}\\ 6& 2& \text{Square planar}\end{array}$