Bonding A level Chem - Help

GoodStudent 1710

4

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Can someone help with this question please ?
Thanks u

Reply 1

have

17

Original post

by GoodStudent 1710

Can someone help with this question please ?
Thanks u

BF3. There are no lone pairs on the central atom (boron)

NF3 -> Nitrogen has lone pair, lone pair on central atom makes it a trigonal pyramadal
H2F -> F has 2 lone pairs, long pairs on central atom makes it V-shaped
CH3OH, the O has 2 lone pairs, which makes the C-O-H bond shape V shaped

Reply 2

Kallisto

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Original post

by GoodStudent 1710

Can someone help with this question please ?
Thanks u

If I am not mistaken, it is A, methanol. The C-atom of methanol has three H-atoms and the OH-group bonded, so there are just bonded electron pairs. That is to say there are no non bonding electron pairs left to be influenced.

Reply 3

Pigster

20

Original post

by Kallisto

If I am not mistaken, it is A, methanol. The C-atom of methanol has three H-atoms and the OH-group bonded, so there are just bonded electron pairs. That is to say there are no non bonding electron pairs left to be influenced.

The shape around the C may be unaffected by lone pairs, but the shape around the O is 2bp, 2lp -> bent.

Reply 4

username2975726

20

Original post

by Kallisto

If I am not mistaken, it is A, methanol. The C-atom of methanol has three H-atoms and the OH-group bonded, so there are just bonded electron pairs. That is to say there are no non bonding electron pairs left to be influenced.

nah its C because BF3 has no lone pairs of electrons. Boron has 3 outer electrons + 3 electrons donated by flourine (1x3) so 6 electrons on the outershell in total. 6/2 = 3 means theres 3 pairs of electrons and since there are 3 flourides they're all bonded, meaning theres no free lone pairs.

Reply 5

Kallisto

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Original post

by Pigster

The shape around the C may be unaffected by lone pairs, but the shape around the O is 2bp, 2lp -> bent.

True! have forgotten to consider the lone pairs around the oxygen. Thanks for corrected this mistake of my own!

But I am a bit confused about this lewis structure. Does this not mean that every single flourine atom has three lone electron pairs? as in the oxygen with the 2 ones on oxygen?

(edited 8 years ago)

Reply 6

Pigster

20

Original post

by Kallisto

But I am a bit confused about this lewis structure. Does this not mean that every single flourine atom has three lone electron pairs? as in the oxygen with the 3 ones on oxygen?

Each F in BF3 has 1bp & 3lp.

I don't understand the comparison you're trying to make to O, though.

Reply 7

GoodStudent 1710

OP

4

Thank u so much

Reply 8

GoodStudent 1710

OP

4

Thankssss

Reply 9

GoodStudent 1710

OP

4

Original post

by StayWoke

BF3. There are no lone pairs on the central atom (boron)

NF3 -> Nitrogen has lone pair, lone pair on central atom makes it a trigonal pyramadal
H2F -> F has 2 lone pairs, long pairs on central atom makes it V-shaped
CH3OH, the O has 2 lone pairs, which makes the C-O-H bond shape V shaped

Thank U

Reply 10

GoodStudent 1710

OP

4

Thanks

Thanks u

Reply 11

Kallisto

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Original post

by Pigster

Each F in BF3 has 1bp & 3lp.

I don't understand the comparison you're trying to make to O, though.

The lone pairs in O in CH3OH are influenced, but the ones for each F in BF3 does not. I wonder why, that is all.

Reply 12

username2975726

20

Original post

by Kallisto

But I am a bit confused about this lewis structure. Does this not mean that every single flourine atom has three lone electron pairs? as in the oxygen with the 2 ones on oxygen?

You only look at the central atom that 'holds' the structure together, which in this case is boron. Since t the 3 pairs of electrons are all bonding pairs, it has no lone pairs to influence the shape.

Reply 13

Pigster

20

Original post

by Kallisto

The lone pairs in O in CH3OH are influenced, but the ones for each F in BF3 does not. I wonder why, that is all.

F bonds to B only. The two nuclei can only be in a straight line. The lp on the F cannot affect the bond angle between the F and B, there isn't an angle to affect.

The O in CH3OH has two bonds, so now you can meaningfully talk about angles: the angle between the line joining the C to the O and the O to the H. That angle is affected by the 2lp also on the O.

Reply 14

Kallisto

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Original post

by Pigster

F bonds to B only. The two nuclei can only be in a straight line. The lp on the F cannot affect the bond angle between the F and B, there isn't an angle to affect.

The O in CH3OH has two bonds, so now you can meaningfully talk about angles: the angle between the line joining the C to the O and the O to the H. That angle is affected by the 2lp also on the O.

Thanks! the angles were the last puzzle in understanding. Now everything makes sense. Thanks for another excellent answer to my question again. :smile:

Reply 15

mislam1.2018

1

Original post

by Kallisto

If I am not mistaken, it is A, methanol. The C-atom of methanol has three H-atoms and the OH-group bonded, so there are just bonded electron pairs. That is to say there are no non bonding electron pairs left to be influenced.