Molecule shapes and bond angles Watch

LeaX
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Could someone please explain why H30+ is pyramidal and NH2- is bent shaped?

H30 surely has 4 pairs - 3 bonded and 1 lone pair which should make it tetrahedral, right? Same with NH2-?
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illusionz
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(Original post by LeaX)
Could someone please explain why H30+ is pyramidal and NH2- is bent shaped?

H30 surely has 4 pairs - 3 bonded and 1 lone pair which should make it tetrahedral, right? Same with NH2-?
You only count atoms and not lone pairs when it comes to assigning the shape of a molecule. You are correct that the electrons occupy a tetraheral structure though.
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thegodofgod
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(Original post by LeaX)
Could someone please explain why H30+ is pyramidal and NH2- is bent shaped?

H30 surely has 4 pairs - 3 bonded and 1 lone pair which should make it tetrahedral, right? Same with NH2-?
Tetrahedral = 109.5o = 4 bond pairs + 0 lone pairs, e.g. CH4, CCl4.

Pyramidal = 107o = 3 bond pairs + 1 lone pair, e.g. NH3.

NH2- is bent shaped (a.k.a. V-shaped / angular) as it has 2 bond pairs + 2 lone pairs, like H2O, giving it bond angles of 104.5o.
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Mallika
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In addition to the other answers, we've been told that Lone pair-lone pair eletron pairs have the greatest repulsion, so the bond angle between them increases, so the other bond angles will decrease by 2.5 degrees, making the bond angle in NH2 104.5 (bent), and the bonding angle in H30+ 107 degrees (pyramidal).
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s.aley
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both of them have 4 regions of electron density around the central atom.

this gives both of them a tetrahedral based shape (109)

they both have roughly 109 degree bond angles, but

NH2 only has 2 bonds that have a 109 degree angle between them

H30 has 3 bonds, with the 109 degrees between them


look at this image

aslong as theres 4 regions of electron density, it will always have those angles (roughly). both NH2 and H30

but for the bent shape, imagine wiping off 2 of the bonds coming out, but keeping the shape the same

and for the pyramidal shape, imagine wiping off 1 of the bonds coming out
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peterson croos
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What is thebond angle nh2
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FlowerFaerie087
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The "standard" tetrahedral bond angle is of a perfect tetrahedron, ie: nearly 109.5°. According to the simpler and not-quite-true-but-good-enough models you use when first learning this, the lone pairs are in closer to the central N atom, so NH2- should be squished in a little more and have a smaller angle than 109.5°.

Also, remember your charges (or unpaired electron dots)... and you know oxygen is O not 0, right? All the elements are letters.
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