Van's Shell Electron Pair Repulsion theory, short named VSEPR theory, says that the geometry of a molecule is based on minimizing the repulsion between electron groups on the central element. Now what exactly do we mean by electron groups? Well, electron groups, we're going to say, equal lone pairs on the central element plus bonding groups. Now when I say bonding groups, I mean the surrounding elements that are connected to the central element. And we're going to say here that our lone pair electrons, which are part of our lone pair, exhibit an electron cloud that further adds to repulsion. So when we talk about VSEPR theory, it's just talking about atoms and lone pairs on the central element will space themselves out to form specific types of shapes. This happens because of the repulsion that exists between the lone pairs and the bonding groups on the central element.
Valence Shell Electron Pair Repulsion Theory (Simplified) - Online Tutor, Practice Problems & Exam Prep
Using VSEPR Theory, locations of surrounding elements and lone pairs around central element can be determined.
Valence Shell Electron Pair Repulsion Theory (Simplified) Concept 1
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Valence Shell Electron Pair Repulsion Theory (Simplified) Example 1
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Here it asks, how many electron groups on the nitrogen atom based on the following Lewis dot structure? So here we have NH3. Now remember, your electron groups equal the lone pair or pairs on the central element plus the bonding groups on the central element. Remember, bonding groups are just these surrounding elements. So if we take a look here, we have 1 lone pair on the central element, plus 1, 2, 3 surrounding elements, which equates to 3 bonding groups. So the total number of electron groups on the nitrogen would be 4.
Valence Shell Electron Pair Repulsion Theory (Simplified) Concept 2
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Here we can say using VSEPR theory, the locations of surrounding elements and lone pairs around the central element are determined. Here, we're going to say that the number of electron groups on the central element can either be 2, 3, or 4. If we take a look here at our molecular shapes, we're going to say when your central element has 2 electron groups, they both are going to be surrounding elements. So, this black ball here represents our central element, and it's connected to 2 surrounding elements or bonding groups. When we have 3 electron groups on the central element, there are 2 possibilities: The central element either has 3 surrounding elements, or it has 2 surrounding elements and one lone pair. When the central element has 4 electron groups, then there are 3 possibilities: the central element could either be connected to 4 surrounding groups, and that's it, or it could be connected to 3 surrounding groups and one lone pair, or it could be connected to 2 surrounding groups and 2 lone pairs. So, just realize the different combinations that exist, and realize the more electron groups that we have on the central element, the more possible shapes that can arise. Now, all you have to remember are electron groups of 2, 3, and 4, so don't worry about going beyond that. And just remember, we're going to go more in-depth in terms of naming these molecular shapes later on.
Using VSEPR Theory, the locations of surrounding elements and lone pairs around the central element are determined.
Valence Shell Electron Pair Repulsion Theory (Simplified) Example 2
Video transcript
How many electron groups, lone pairs, and bonding groups does the compound have respectively? Alright. So electron groups, we're going to abbreviate as EG, lone pairs on the central element as LP, and bonding groups as BG. Alright. So lone pairs on the central element. We have one lone pair on the central element. Bonding groups are the surrounding elements attached to that central element. That'd be 1, 2 bonding groups. That means we have a total of 3 electron groups. Alright? So we'd say we have 3 electron groups, 1 lone pair, and 2 bonding groups for this particular compound.