Return to Contents Chapter 2 : Alkanes  Ch 2 contents
Bonding and Hybridisation Answers
 
Ans 1:
 

 

No, a π bond is not symmetric with respect to the internuclear axis. Rotation about the axis along the bond between the two nuclei produces no change in the view of a σ bond (top pair) but rotation about the axis along the bond switches the lobes of the orbitals in the π bond (bottom).

Ans 2 :  Allene  H2C=C=CH2 first look at how many groups each C is attached to, the answer is colour coded below:

Therefore,  there are 2 sp2 and 1 sp hybridised C atoms. Note that this example highlights an example of an sp hybridised C that is not part of an alkyne C≡C
Ans 3 :  Again we need to look at the groups attached to the C atoms in question:
Therefore the bond that attaches the methyl group to the double bond is a σ bond formed by the intereraction of a C sp3 and a Csp2 orbitals.
Ans 4:
 

 

The molecule H22- is isoelectronic with He2, so like diatomic helium, this is an unstable molecule.
In order to be able to "work-out" an answer to the problem, we should draw out the molecular orbital diagram for the interaction of two H atoms as shown to the right.   The only difference compared to regular H2 is the number of electrons. Since H22- is a four electron system, we are forced to use the
s*-anti-bonding orbital so destabilising the system.

 © Dr. Ian Hunt, Department of Chemistry, University of Calgary