[sankalpmittal]

Hello , I'm a new member here. 

Hydrogen Fluoride (HF) contains 3 lone pairs and one bond pair. Then how the bond angle of it is measured ? According to Valence Shell Electron Pair Repulsion theory (VSEPR) , its bond angle should be 103 degrees , but its 92.5 degrees. Why is it so ?

[curiouscat]

How does a diatomic molecule have   a bond angle (other than 180 that is)?

Maybe I don't see what you mean.

[sankalpmittal]

How does a diatomic molecule have   a bond angle (other than 180 that is)?

Maybe I don't see what you mean.

Yes , I too thought that the geometry of HF must be linear and it must have bond angle of 180. But its not so. Hybridization of HF is sp3 and I was told that compounds having hybridization of sp3 should have a bond angle of 109 degrees. (Why is it so ?) As lone pair increases in sp3 hybridization , the bond angle keep on decreasing. Example is that H2O of sp3 hybridization has bond angle 105 degrees.

Order of bond angle in sp3 hybridization is as follows :

CH4 : lone pair : 0 Bond pair : 4 Bond angle : 109
NH3 : lone pair : 1 Bond pair : 3 Bond angle : 107
H2O : lone pair : 2 Bond pair : 2 Bond angle : 105

By seeing the following pattern , bond angle of HF should be 103 degrees , but its 92.5 degrees (HF : lone pair : 3 Bond pair : 1). Why is it so ? That's what I am asking.

[Borek]

Where did you got the bond angle for HF from?

[sankalpmittal]

Where did you got the bond angle for HF from?

Our school teacher told us. My guess is also that bond angle of HF should be 180 degree , but he told that its 92.5 . Either he is wrong or I  , or there is also a possibility that he is telling the bond angle when "two" HF molecules get bonded via "hydrogen bond".

[AWK]

Old quantum theory - hybridization index
eg:
http://courses.chem.psu.edu/chem210/mol-gallery/hybridization/hybrids.html

[curiouscat]

Either he is wrong or I  , or there is also a possibility that he is telling the bond angle when "two" HF molecules get bonded via "hydrogen bond".

The H-bonding angle is 116 degrees as per Wikipedia; so wrong again.

[curiouscat]

Old quantum theory - hybridization index
eg:
http://courses.chem.psu.edu/chem210/mol-gallery/hybridization/hybrids.html

From this site:

Strictly speaking, in this case the hybrid cannot be determined just from the bond angle. An angle between any two sp-type hybrids is always 180°, regardless of their specific s characters. In this case,

[sankalpmittal]

Either he is wrong or I  , or there is also a possibility that he is telling the bond angle when "two" HF molecules get bonded via "hydrogen bond".

The H-bonding angle is 116 degrees as per Wikipedia; so wrong again.

Ah thanks !! Anyways HF is sp3 hybridization. So bond angle of a diatomic compound is 180 i.e its geometry is linear , no matter which hybridization it undergo. Am I correct ? Or is it better to say that diatomic molecules have no bond angle ?

[Borek]

Or is it better to say that diatomic molecules have no bond angle ?

For me that's the only logical answer. Angle is between two objects (lines, vectors, line segments, surfaces and so on) connected at a vertex. You have one object.

[curiouscat]

Or is it better to say that diatomic molecules have no bond angle ?

For me that's the only logical answer. Angle is between two objects (lines, vectors, line segments, surfaces and so on) connected at a vertex. You have one object.

I totally agree. It is silly to speak of an angle in a A-B entity. Doesn't matter if A and B are atoms, molecules, balls, planets whatever you might have.

An angle needs an A-B-C system.

[sankalpmittal]

Well thanks for your replies !!