Valence Shell Electron Pair Repulsion Theory - Video Tutorials & Practice Problems
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VSEPR Theory
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concept
Valence Shell Electron Pair Repulsion Theory Concept 1
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Now under valence shell electron pair repulsion theory, also known as VSEPR 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, electron group equals a lone pair or lone pairs on the central element plus bonding groups. Now when we say bonding groups, we're referring to the surrounding elements that are directly attached to our central element. Now in addition to this, we can say that our lone pair electrons, they exhibit an electron cloud that further adds to repulsion. So we're gonna start looking at different types of molecular shapes, and we're gonna see the number of electron groups associated with each one of these unique molecular shapes.
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example
Valence Shell Electron Pair Repulsion Theory Example 1
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51s
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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 3 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 gonna say we have 1, 2, 3, 4 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 loop here. 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 3 bonding groups on the nitrogen atom giving us a total of 4 electron groups.
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Valence Shell Electron Pair Repulsion Theory Concept 2
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Using VSEPR 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 you're 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 to 6. 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 2 electron groups. There's only one possible molecular shape associated with it. It's a central element connected to 2 bonding groups or surrounding elements. When we have 3 electron groups around the central element, 2 possible shapes can happen. 1 where we have 3 surrounding elements, and one where we have 2 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, then 3 shapes are possible. 1 where all 4 electron groups are surrounding elements, one where it's 3 surrounding elements, 1 lone pair, and one where it's 2 surrounding elements and 2 lone pairs. If you have 5 electron groups, this is the most complex of all of them because it gives us 4 different shapes. Here, we'd have our first option where it's 5 surrounding elements, one where it's 4 surrounding elements and 1 lone pair, one where it's 3 surrounding elements and 2 lone pairs, and finally, one where it's 2 surrounding elements and 3 lone pairs. Finally, when we have 6 electron groups around the central element, we have 3 possible shapes. One where it's 3 surrounding elements 6 surrounding elements around the central element, then one where it's only 1 lone pair and 5 surrounding elements, and then one where it's 2 lone pairs and 4 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.
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example
Valence Shell Electron Pair Repulsion Theory Example 2
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51s
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How many electron groups, lone pairs, and bonding groups does the compound have respectively? So here we have s e f 4. 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 s e f 4.
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