Electron Geometry - Video Tutorials & Practice Problems
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The simplest system for geometrical shapes that focuses on the number of electron groups around the central atom.
Electron Geometry
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concept
Electron Geometry Concept 1
Video duration:
3m
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Hey everyone. So when we say electron geometry, realize that it represents the simplest system for geometrical shapes that focuses on the number of electron groups around the central element. When it comes to the electron geometry we're going to treat lone pairs and surrounding elements as the same. So if we take a look here at this chart we are breaking things down in terms of number of electron groups, the orbital shapes where we just give certain examples that fit this particular row, the electron geometry name, and then a memory tool to help us remember that electron geometry name. So here we're going to start out with the first one, and let's say that our molecule has 2 electron groups. Here we have carbon dioxide as our example. Carbon is a central element. It has 2 surrounding elements, so that's why it has 2 electron groups. The geometry here, the electron geometry, would be called linear. And a good way to remember linear is that recall that there are 2 points in a straight line. Okay? So line for linear and two points because there's 2 electron groups. So again we have carbon in the center and we have 2 electron groups, these 2 oxygens. For the next one we have 3 electron groups, and remember these electron groups could either be 3 surrounding elements, or they could be 2 surrounding elements and 1 lone pair. Remember we're treating lone pairs and surrounding elements as the same. In this case the electron geometry name would be trigonal planar. Now the beauty of chemistry is that we can pronounce things differently, but all that really matters is that you get the spelling correct. Okay. So you might hear trigonal planar, trigonal planar, trigonal planar, trigonal planar, none of that matters, just make sure you're spelling it correctly. And how do we remember this? Well, we're going to say we have 3 electron groups and it starts with tri, tri meaning 3. Next we have 4 electron groups, and remember that could just be different situations where they're all surrounding elements or they're surrounding elements with a mixture of lone pairs. As long as it adds up to 4 electron groups it fits in this row. Here the electron geometry name would be tetrahedral. Tetra means 4 4 electron groups. Now the next 2, let's look at the next 2. We have 5 electron groups for the next one, So the central element has 5 electron groups around it, which could be all surrounding elements or a combination of surrounding elements and lone pairs. Right? So here we have 3 surrounding elements, 2 lone pairs, still that's up to 5. Here we have 2 surrounding elements and 3 lone pairs. Now the name for this one, this one's a bit longer, this is trigonal or trigonal bipyramidal. Now Jules, how am I supposed to remember this name? Well, we know that it has 5 electron groups, and we're gonna say here tri means 3, bi here means 2. 3+2 will give me 5. Alright, finally we have 6 electron groups, so again that could be a combination of all surrounding elements that add up to 6 or some combination of surrounding elements and lone pairs. This one, its name is octahedral. This one is going to require a little bit more imagination in terms of remembering it. Octa, you might say, hey, Jules, octa means 8. But here we're talking about 6 electron groups. Well, we can play on this idea of octa meaning 8. So octa octopus. So an octopus has 8 tentacles, right, or 8 legs and it has 2 eyes. So 8 tentacles-28-two gives me 6. 6 electron groups. So remember if you have 6 electron groups your electron geometry is octahedral. So just remember some of these memory tools if it's hard for you to remember a particular electron geometry name, and you'll be able to get through this. Remember, in the case of electron geometry, lone pairs on the central element and surrounding elements are treated as the same.
The electron geometry of a compound treats surrounding elements and lone pairs on the central element as the same.
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example
Electron Geometry Example 1
Video duration:
48s
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Determine the electron geometry for the hydrogen sulfide molecule, h two s. So if we take a look at hydrogen sulfide or, yeah, sulfide molecule, we're gonna see here that it is a central element sulfur connected to how many electron groups? It's connected to 1, 2, 3, 4 electron groups. Remember, electron groups represent lone pairs on the central element, as well as surrounding elements directly connected to the central element. So we have 4 electron groups, and remember 4 is connected to tetra. Because it's connected to tetra, this electron geometry will be tetrahedral. So hydrogen sulfide has a tetrahedral electron geometry.
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Problem
Problem
Determine the electron geometry for the carbon disulfide molecule, CS2.
A. Linear
B. Bent
C. Trigonal planar
D. Tetrahedral
A
Linear
B
Bent
C
Trigonal planar
D
Tetrahedral
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example
Electron Geometry Example 2
Video duration:
1m
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Recall there are many possible Lewis dot structures that exist, but there are rules to draw the best structure. So for this example, it says, determine the electron geometry for the following molecule, c h two o. This is also called formaldehyde. So if we take a look here, we place the least electronegative element in the center. Now that would be hydrogen, but remember we have another rule when it comes to hydrogen. It can never go in the center. So as a result, it's carbon that has to go in the center. Carbon is in group 4 a, so it has 4 valence electrons, and remember hydrogens are group 1a and they can only form single bonds. Carbon itself has to make 4 bonds. It's already making 2 bonds, it needs 2 more. The only element that's left is oxygen, so carbon would have to form a double bond to that oxygen. Carbon oxygens in group 6 a's would have 6 valence electrons and here we're showing all of them. So this will represent the structure or molecular shape of formaldehyde. Now if we take a look, we'd say that the carbon is connected to how many electron groups? It's connected to 1, 2, 3 electron groups. Remember 3, we say tri equals 3, Because we're saying tri, that would mean that the electronic geometry is trigonal planar. So this would be the electronic geometry or molecular shape of the formaldehyde molecule.
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Problem
Problem
Determine the number of electron groups for the following cation:AsBr2+.
A. 2
B. 3
C. 4
D. 1
A
2
B
3
C
4
D
1
6
Problem
Problem
Draw and determine the electron geometry for the following molecule:TeBr4
Video duration:
1m
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7
Problem
Problem
Determine the electron geometry of the nitrogen atom within methylamine, CH3NH2.