Question

In allene $(C_3H_4)$ the type(s) of hybridisation of the carbon atoms, is (are)

• A. $sp \,$ and$ \, sp^3$
• B. $sp \,$ and $\, sp^2$
• C. only $\, sp^3$
• D. $sp^2 \,$ and$ \, sp^3$

Answer 1

Answer: (B)

Allene is the name given to propdiene, $\underset{\text{Allene}}{H_2C = C = CH_2}$
Hybridisation of an atom is determined by determining the
number of hybrid orbitals at that atom which is equal to the
number of sigma $(\sigma)$ bonds plus number of lone pairs at the
concerned atom.
Pi$(\pi)$ bonds are not formed by hybrid orbitals, therefore, not counted for hybridisation.
Here, the terminal carbons have only three sigma bonds
associated with them, therefore, hybridisation of terminal carbons
is $sp^3$. The central carbon has only two sigma bonds associated,
hence hybridisation at central carbon is $sp$