Please can you help me with bond angles?

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C_Yap
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#1
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So there are a few names and bond angles I'm still confused about:

5BP 0LP is trigonal bipyramidal (90 degrees and 120 degrees)
4BP 1LP is seesaw (but what is the bond angle, that will get me the mark in the exam?)
3BP 2LP is t-shaped (what is the bond angle?)

6BP is octahedral (90 degrees)
5BP 1LP is square pyramidal (what is the bond angle?)
4BP 2LP (what is the bond angle?
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C_Yap
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Sorry for bumping, but I really need some clarification on this.
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Jpw1097
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(Original post by Baaah)
So there are a few names and bond angles I'm still confused about:

5BP 0LP is trigonal bipyramidal (90 degrees and 120 degrees)
4BP 1LP is seesaw (but what is the bond angle, that will get me the mark in the exam?)
3BP 2LP is t-shaped (what is the bond angle?)

6BP is octahedral (90 degrees)
5BP 1LP is square pyramidal (what is the bond angle?)
4BP 2LP (what is the bond angle?
Image

I would normally just take 2-3° off the angle for each lone pair due to the repulsion. So 4bp 1lp would have angles of approximately 88° and 118°. As for 3bp 2lp, the geometry can be trigonal planar (in which case the bond angles are 120°) or T-shape - in which case the bond angle is approximately 85° as the two lone pairs means more repulsion.
As for square pyramidal, the angles are likely to be around 87-88°. Of course, for square planar (4bp 2lp) the angles are 90° as the lone pairs exert equal but opposite repulsion. I don't think there are precise bond angles, so just looking at the geometry and taking 2-3° off the normal bond angle for each lone pair should do.
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C_Yap
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(Original post by Jpw1097)
Image

I would normally just take 2-3° off the angle for each lone pair due to the repulsion. So 4bp 1lp would have angles of approximately 88° and 118°. As for 3bp 2lp, the geometry can be trigonal planar (in which case the bond angles are 120°) or T-shape - in which case the bond angle is approximately 85° as the two lone pairs means more repulsion.
As for square pyramidal, the angles are likely to be around 87-88°. Of course, for square planar (4bp 2lp) the angles are 90° as the lone pairs exert equal but opposite repulsion. I don't think there are precise bond angles, so just looking at the geometry and taking 2-3° off the normal bond angle for each lone pair should do.
Wow thanks!

I was basically confused because a lot of tables I found are wrong (I found one that said square pyramid is exactly 90 degrees bond angle)

I was also confused before because I didn't know what <90 degrees meant.

Thanks for clarifying everything!
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Jpw1097
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(Original post by Baaah)
Wow thanks!

I was basically confused because a lot of tables I found are wrong (I found one that said square pyramid is exactly 90 degrees bond angle)

I was also confused before because I didn't know what <90 degrees meant.

Thanks for clarifying everything!
The reason they say <90° is because there's no real precise value, like I say, just taking 2-3° is about right.
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Ninja_R
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#6
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Check out the bond angle (VSEPR Theory) videos by Tyler Dewitt on YouTube.
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MexicanKeith
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(Original post by Jpw1097)
The reason they say <90° is because there's no real precise value, like I say, just taking 2-3° is about right.
As already mentioned, knocking off a few degree for each lone pair is not unreasonable.

Expecting you to know the exact angles for the more unusual geometries would be unreasonable (in reality they vary slightly from compound to compound) so, as long as you know the values for TBP, trigonal planar, octahedral, "bent" (ie water), trigonal pyramidal (ie ammonia) and tetrahedral you should be alright. Some other geometries may be asked, but hopefully they should be obviously if you can visualise them
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C_Yap
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(Original post by MexicanKeith)
As already mentioned, knocking off a few degree for each lone pair is not unreasonable.

Expecting you to know the exact angles for the more unusual geometries would be unreasonable (in reality they vary slightly from compound to compound) so, as long as you know the values for TBP, trigonal planar, octahedral, "bent" (ie water), trigonal pyramidal (ie ammonia) and tetrahedral you should be alright. Some other geometries may be asked, but hopefully they should be obviously if you can visualise them
Hey thanks!

I was confused at first because different websites/images showed different bond angle values. Thanks for clearing it up!
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