Question

Geometry of molecules in which the central atom has no lone pair of electrons

Answer 1

The Way of Chemistry

Molecules In Which The Central Atom Has No Lone pair

Good day! I’m here to discuss the first of the two types of molecular geometry, the molecule in which the central atom has no lone pairs. But first of all, what is molecular geometry?

Molecular geometry is the three dimensional arrangement of atoms in a molecule or compound. It follows the Valence Shell Electron Pair Repulsion theory, also known as VSEPR. It assumes that each atom in a molecule will be positional so that there is minimal repulsion between the valence electrons of that atom.

The following are the two types of molecular geometry:

A. Molecule in which the central atom has no lone pairs;

B. Molecule in which the central atom has no lone pairs.

Our intention for this article is to discuss and clearly understand the first type of molecular geometry, so here it is.

A. Molecule in which the central atom has no lone pairs

Writing the geometry of molecules requires the following format:



As mentioned in the picture above, “A” stands for the central atom, “B” stands for the surrounding atoms, and “x” stands for the number of B atoms. This will be used in finding out the geometrical structure of the compound/ molecule.

The following are the molecules in which the central atom has no lone pairs:



AB2

This molecule has two surrounding atoms and its structure is linear. The angle of separation of the surrounding atoms from each other is 180˚. The simplest example of this molecular geometry is Beryllium chloride or BeCl2.

To find out what to do in order to arrange the atoms, familiarize yourself with the following steps:

1. Get the number of electrons to be distributed in the atoms of the molecule. Add the number of electrons of the atoms present in the molecule and subtract the number of bonded electrons from the sum of it.

2. Make a Lewis Structure of the compound and distribute the electrons.

3. If you wanted to, make a three dimensional figure of the compound.

First, we have to get the number of electrons to be distributed in the atoms of the molecule by simply adding the number of electrons of the atoms present in the molecule and by subtracting the number of bonded electrons. 


For example is the Calcium Iodide. Calcium is from group 2 and Iodine is from group 7.Compute for the no. of electrons to be distributed

CaI2 = 2 + 2(7) = 16e­- - 4e- = 12e-

Distribute the electrons






AB3

This molecule has three surrounding atoms and its structure is a trigonal planar. The angle of separation of the surrounding atoms from the each other is 120˚. Indium chloride is an example of this molecular geometry.

InCl3 = 3 + 3(7) = 24 e- - 6e- = 18e­-




AB4

Four atoms are surrounding the central atom and the structure is tetrahedral. The angle of separation of the surrounding atoms from each other is 109.5˚.

Xenon fluoride is an example of a compound with a tetrahedral structure.

XeF4 = 8 + 4(7) = 36 e- - 8e- = 28e­-





AB5

There are five atoms that surround the central atom and the structure is a trigonal bipyramidal. The angles of separation of the surrounding atoms from each other are 90˚ and 120˚.

Antimony (V) fluoride is an example of a compound with a trigonal bipyramidal structure.

SbF5 = 5 + 5(7) = 40 e- -10e- = 30e­-



AB6

Six atoms are surrounding the central atom and its structure is octahedral. The angle of separation between the atoms is 90˚.

Uranium (VI) bromide is a compound with an octahedral structure.

UBr6 = 6 + 6(7) = 48 e- -12e- = 36e­-





To generalize, here is a table for the geometry of molecules with a central atom which has no lone pairs.

That’s all for the discussion of the molecules in which the central atom has no lone pairs.