Final answer:
A π bond (pi bond) is present in species where there is a side-by-side overlap of two p orbitals, such as in ethene (C2H4), which contains a double bond with one sigma and one pi bond.
Step-by-step explanation:
The species that contains a π bond (pi bond) can be identified by understanding the nature of covalent bonding. A π bond is a type of covalent bond that results from the side-by-side overlap of two p orbitals. In contrast, a sigma (σ) bond is formed by the end-to-end overlap of orbitals, with the electron density concentrated along the internuclear axis. A molecule such as ethene (C2H4) contains a double bond between the carbon atoms consisting of one sigma bond and one π bond. The π bond is characterized by a nodal plane containing the nuclei with electron density localized on both sides of this plane, while sigma bonds have circular cross-sections of electron density around the internuclear axis.
To distinguish between sigma and pi bonds in specific examples:
- (a) Side-by-side overlap of a 4p and a 2p orbital depicts a π bond.
- (b) End-to-end overlap of a 4p and a 4p orbital depicts a sigma (σ) bond.
- (c) End-to-end overlap of a 4p and a 2p orbital also depicts a sigma (σ) bond.