(a) The H2C═ group has sp hybridization, and (b) the ═C═ atom has sp2 hybridization.
In the allene molecule (H2C═C═CH2), the central carbon atom participating in the double bond exhibits sp2 hybridization. This hybridization involves the combination of one s orbital and two p orbitals, forming three sp2 hybrid orbitals in a trigonal planar arrangement around the carbon atom.
On the other hand, each terminal carbon atom attached to a hydrogen atom has sp hybridization. The terminal carbon atoms form two sigma bonds with hydrogen and one sigma bond with the adjacent carbon, using the combination of one s orbital and one p orbital to form two sp hybrid orbitals in a linear arrangement.
The unique hybridization patterns of sp2 and sp orbitals in the allene molecule contribute to its linear geometry, where the three carbon atoms lie on a straight line. Understanding the hybridization state of carbon atoms is crucial for predicting molecular shapes and properties in organic chemistry.