shape of water

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shape of water

Postby tatianatumbling_1J » Wed May 23, 2018 3:20 pm

is water still considered trigonal pyramidal even though it has 2 lone pairs?

Mohamad Farhat 1L
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Re: shape of water

Postby Mohamad Farhat 1L » Wed May 23, 2018 4:11 pm

I think it matters how many 90 degree lp-bp interactions there are rather than how far apart the lone pairs are.

Solene Poulhazan
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Re: shape of water

Postby Solene Poulhazan » Wed May 23, 2018 4:13 pm

Water has 8 electrons around the central oxygen atom. This means there are four electron pairs arranged in a tetrahedral shape. There are two bonding pairs and two lone pairs.

Steven Luong 1E
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Re: shape of water

Postby Steven Luong 1E » Thu May 24, 2018 12:28 am

No. The shape of water is bent due to the 2 lone pairs repelling one another, pushing the O-H bonds down to form a bent shape.

Tina Wen 1G
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Re: shape of water

Postby Tina Wen 1G » Thu May 24, 2018 9:08 am

I thought this was the name of a movie haha. But anyways the shape should be bent. The shape is first more determined by the number of bonding pair which is 2 in this case. And then consider the presence of lone pairs which results in repulsion and distortion of the linear structure. A trigonal pyramidal structure would be something like NH3 which has 3 bonding pairs already and then bent to the pyramidal shape by one lone pair.

Jacy Black 1C
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Re: shape of water

Postby Jacy Black 1C » Fri May 25, 2018 11:45 am

I do think that Lavelle really emphasized that the lone pairs don't play a role in the naming of shape, although it does affect the overall shape. This is important to know, and is a large part of the reason why the shape isn't pyramidal but bent.

Sara Veerman-1H
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Re: shape of water

Postby Sara Veerman-1H » Fri May 25, 2018 12:20 pm

I think shape is named based on the amount of bonds there are. However, the amount of lone pairs do alter the shape of the molecule. Water, because the central atom is only bonded to 2 other atoms, cannot be named trigonal pyramidal (trigonal pyramidal implies there are 3 bonds to the central atom and one lone pair making a similar shape to a tetrahedral) instead it is named bent (VSEPR formula: AX2E2).

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Re: shape of water

Postby 304984981 » Sun May 27, 2018 9:22 pm

Water molecule has a BENT SHAPE
Although it has 4 regions of electronic density, which mean it is arranges tetrahedrally
But 2 of the regions are because of lone pairs, while 2 others are bonding pairs
So it causes a larger repulsion than the tetrahedral(109.5), also larger than the trigonal pyramidal(107.5) which contains 3bonding pair,1 lone pair. eg NH3
So this greater repulsion squeeze the bond anlge, making it smaller to be 106

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Re: shape of water

Postby ramayyala1G » Sun May 27, 2018 10:26 pm

Keep in mind you do not need to know the bond angle for this shape because it varies from molecule to molecule. 106 degrees is not the standard bent shape angle.

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