Chapter 1.10, Problem 28PTS

Interpretation Introduction

Interpretation: The geometry for carbocations and carbanions has to be predicted

Concept Introduction:  According to VSEPR (Valence Shell Electron Pair Repulsion) theory, each molecule gets a unique structure. That structure is explained by considering steric number of that molecule.

The steric number is the combination of both number of σ-bonds and number of lone pairs involved in a particular molecule.

σ-bonds are formed by the mutual sharing of electrons between the two atoms.  As a result, bond between two atoms is formed.  This type of bond is called covalent bond.  In this process, bonding electron pairs are involved.

Non-bonding electrons are not involved in the bond formation.  They are called lone pairs.

The geometry of the atom will be determined by counting the steric number followed by the hybridization state of that atom and finally electronic arrangement of atoms in space.

If the steric number is 4, the atom or ion has sp³ hybridization and the electronic arrangement of atoms in space (i.e. geometry) will be tetrahedral.

If the steric number is 3, the atom or ion has sp² hybridization and the electronic arrangement of atoms in space (i.e. geometry) will be trigonal planar.

If the steric number is 2, the atom or ion has sp hybridization and the electronic arrangement of atoms in space (i.e. geometry) will be linear.

To find: Comparing the structures of carbocation and carbanion and assigning the correct geometry to each ion