Valence Shell Electron Pair Repulsion Theory - Online Tutor, Practice Problems & Exam Prep

Valence Shell Electron Pair Repulsion Theory Concept 1

Now under valence shell electron pair repulsion theory, also known as Vesper theory, we say that the geometry of a molecule is based on minimizing the repulsion between electron groups on the central element.

Now when we say the term electron group, an electron group equals a lone pair or lone pairs on the central element plus bonding groups. Now when we say bonding groups, we are referring to the surrounding elements that are directly attached to our central element.

In addition to this, we can say that our lone pair electrons exhibit an electron cloud that further adds to repulsion. So we're going to start looking at different types of molecular shapes and we're going to see the number of electron groups associated with each one of these unique molecular shapes.

Valence Shell Electron Pair Repulsion Theory Example 1

How many electron groups on the nitrogen atom based on the following Lewis dot structure. So here we have a picture of ammonia. Ammonia has one lone pair and three surrounding elements. Remember your electron groups equal the number of lone pairs on the central element as well as the number of bonding groups which are just the number of surrounding elements.

So if we take a look here we're going to say we have 1234 electron groups on the nitrogen atom. Also realize here when we talk about a lone pair, it's just a pair of electrons not forming a bond. And remember they exhibit an electron cloud. So we see this electron cloud as this low pier.

This just helps push bonds further away from itself, causing even more repulsion within our molecule. So again in this particular question, we have 1 lone pair and three bonding groups on the nitrogen atom, giving us a total of 4 electron groups.

Valence Shell Electron Pair Repulsion Theory Concept 2

Using Vesper theory, the locations of surrounding elements and lone pairs around the central element are determined. Now it's important to realize that remember lone pairs cause further repulsion in terms of a molecular shape and the molecular shapes are going to see are drawn that way on purpose. These are the actual arrangements of the atoms based on the number of electron groups around the central element.

So if we take a look here, we have electron groups that go from 2:00 to 6:00 and based on your number of electron groups we can produce different types of molecular shapes. If we take a look at the first electron group pairing, we have two electron groups. There's only one possible molecular shape associated with it. It's a central element connected to two bonding groups or surrounding elements.

When we have 3 electron groups around the central element, 2 possible shapes can happen. One where we have 3 surrounding elements and one where we have two surrounding elements and 1 lone pair. Remember lone pairs? Again they have an electron cloud around them, which we show with this lobe.

If we have 4 electron groups and three shapes are possible, one where all four electron groups are surrounding elements, one where it's 3 surrounding elements, 1 lone pair, and one where it's two surrounding elements and two lone pairs. If you have 5 electron groups, this is the most complex of all of them, because it gives us four different shapes.

Here we'd have our first option, where it's five surrounding elements, one where it's 4 surrounding elements in one lone pair, one where it's 3 surrounding elements and two lone pairs, and finally one where it's two surrounding elements and three lone pairs. Finally, when we have 6 electron groups around the central element, we have three possible shapes, one where it's 6 surrounding elements around the central element. Then one where it's only 1 lone pair and five surrounding elements, and then one where it's 2 lone pairs and four surrounding elements.

Now as we go deeper and deeper in terms of shapes, we'll learn the names associated with each one of these molecular shapes shown. But again, remember the number of electron groups kind of limits the different types of molecular shapes that are possible for any given molecule.

Valence Shell Electron Pair Repulsion Theory Example 2

How many electron groups, lone pairs and bonding groups does the compound have respectively? So here we have SEF₄. Now if we look at the total number of electron groups, remember electron groups takes into account the lone pair as well as the bonding groups on the central element.

So we have 1, 2, 3, 4, 5 total electron groups, lone pairs, lone pairs on the central element. Remember they have an electron cloud. So we have one lone pair on our central element and then bonding groups are just the surrounding elements attached to the central element.

So that is 1, 2, 3, 4 bonding groups. So this is how we break down the different types of groups found within SEF₄.