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Hello there! And welcome, to Pinch of KCN the Blog! Well thank you for visiting us again, currently we've finally reach 3,000 page views, which is kind of unbelievable.
Anyways, back to today's topic, the VSEPR Theory. To be honest, I think it is one the of weirdest theory with the weirdest diagrams and the weirdest name in chemistry history. Nevertheless, we are here to help you further understand this concept, and I must warn you that it requires decent skills on drawing Lewis Dot Diagrams, especially with covalent bonds. If you're still unsure, we highly recommend you to read our previous blog before leanring the VSEPR Theory.

Feeling confident?

Feeling CONFIDENT? Then let's start!

When you first saw the name of this theory, you must be wondering what "VSEPR" stands for, well, it's original name was "Valence Shell Electron Pair Repulsion Theory". Long name, huh? That's why lazy chemists have shortened its name in VSEPR.

What is the VSEPR Theory?
Valence shell electron pair repulsion (VSEPR) rules are a model in chemistry used to predict the shape of individual molecules based upon the extent of electron-pair electrostatic repulsion. The premise of VSEPR is that the valence electron pairs surrounding an atom mutually repel each other, and will therefore adopt an arrangement that minimizes this repulsion, thus determining the molecular geometry. [ctrl+v directly from Wikipedia,the not-so-trusty website]
In our own (and simpler) words, it means that the VSEPR helps to create a geometric model which shows the approximated position of the electrons of all covalent bond molecules. And where like electrons repel each other, their positions tend to be separated from each other as far as possible.
In general, there are about 5-6 simple steps to draw the VSEPR model, of course, if you have your own secret way of doing it, we highly recommend you to use that technique.

Modelling VSEPR with single atomic centered compounds
Single atomic centered compounds are molecules which they have a distinct element surrounded by another series of one-of-a-kind elements. (Eg. CH4, CCl4, and NH3) Now, let's use methane as the example for demonstration.
First, determine the total number of valence electrons of the compound. (Please don't tell me you don't know how to count valence electrons!!（╬￣皿￣）)
C = 4
H4 = 1 x 4= 4
Total number of valence electrons = 4 + 4 = 8
Secondly, draw the Lewis diagram for this compound, which is....

OR

I personally prefer the left one because it gets frustrated when you have drew dots in your chemistry test diagram and your teacher has decided that you did not. 

Thirdly, divide the total number of valence electrons by "2" to get the total coordination number.

CH4 total coordination number = 8/2 = 4

Fourthly, determine the geometric pattern which the compound will be in. The 5 different patterns are shown below:

2 Balloons =linear geometry
3 Balloons =trigonal planar geometry
4 Balloons =tetrahedral geometry
5 Balloons = trigonal bipyramidal geometry
6 Balloons = octahedral geometry
Now, imagine each balloon as one coordination number ; for methane, it has 4 coordination number , so it'll have a tetrahedral geometry shape.
Fifthly, draw the diagram with your artistic skills

Notice that there is a bond angle of 109.47, because like elements tend to repel each other. Well, you might want to ask, how do we know the bonding angle of these compounds, we can't just use a protractor to measure it, can't we?
No worries, here's a useful chat for you.

The AXE system

In the AXE system, you'll see weird formulas with letters like AXmEn. These formulas give you a hint of what the compound should shape like.

A = Central atom
m = The number of molecules or ions surrounding the central metal ion X (also called "ligands")
n = Number of non-bond lone pairs
E = Unbonded electron pairs on the central atom

For example, CH4 will be AX4.

So that's all for today's lesson! Feel stressed out?
Well, I'm not surprise if you said yes—everyone feels tired after reading long passages.
So here's an easy rubric cube for you, now solve it in 1 second.

Challenge denied.