103.CHEMICAL BONDING (50)- Practice Problems.

Q:  Why is o- hydroxy benzaldehyde a liquid whereas p-hydroxy benzaldehyde a solid , with high MP, at room temperature ?

A: o- hydroxy benzaldehyde has intramolecular H- bonds and so the molecules are not very tightly bound to each other as in the case of p-hydroxy benzaldehyde , where, the intermolecular H-bonds hold molecules together, making it a high melting solid.



Q: What type of C-C bond is highlighted in red in the figure below?

i.σ(C2sp3,C2sp3) and π (C2sp3,C2sp3)
3,C2sp3)  and σ (C2sp3,C2sp3)
iii.σ(C2sp2,C2sp2) and π (C2sp2,C2sp2)
2,C2sp2) and π (Cpy,Cpy

A: First thing to understand is that – ONE SHOULD NOT GET SCARED BY SEEING SUCH A COMPLEX STRUCTURE. The question is only related to a double bond in the structure.So let’s focus only on that part.

We know that when there is a double bond, one bond is a sigma bond(σ) and the other is a pi(π) bond. So, we can rule out option no ii as it has no π bond component. We also know, that a π bond is made from p-orbitals. Thus, we can rule out option no i and iii , as they don’t have a π bond with p-orbitals. Thus, the answer to the above question is – option no iv.

Q:Why ClF2 is a linear but ClF2+ is a bent molecular ion?

A: The hybridization of these two ions are responsible for their respective structures. How do we find the hybridization? We know that,

1033.jpgChlorine and fluorine both have 7 electrons in their valence shell. 

ClF2 ion – 

∴Total no of  valence electrons  for  ClF2 = 7 + 2(7) + 1 = 22. (We add 1 for the negative charge).
Out of the 22, 4 electrons are bonding and 18 electrons make 9 lone pairs.  Now let us draw the Lewis structure of this molecule. Chlorine is less electronegative , so it will be the central atom.After two bonds are formed, we have to arrange 9 lone pairs over the three atoms.Each atom has three lone pairs as shown below – 


The chlorine has 10 electrons on it , in this structure – thus Cl has an expanded octet here.

no. of hybrid orbitals for chlorine = 2 + 3 = 5. Thus, it is sp3d hybridized. So, this should have a triagonal bipyramidal geometry. But as we studied in post 73-


So, the LPs will occupy the equatorial positions.Thus, the structure will be as follows – 


Thus, if we ignore the LPs then the molecule will look linear(180º).


Total no of  valence electrons  for  ClF2+ = 7 + 2(7) – 1 = 20. (We subtract 1 for the positive charge).

Out of 20 electrons i.e 10 pairs, 2 are bonding.Thus, we have to arrange 8 pairs on three atoms.The Lewis structure can be drawn as follows – 


The structure in this case will be as follows – 


This ion has a bent geometry as seen in the above figure.


In the next post we shall start discussing a new topic .Till then,

Be a perpetual student of life and keep learning ….

Good day !









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