Final answer:
In HCN, there are two σ (sigma) bonds and two π (pi) bonds. CO₂ contains two sigma bonds and two pi bonds due to its double bonds with oxygen. CO has a triple bond between carbon and oxygen, implying one sigma bond and two pi bonds plus a lone pair on carbon.
Step-by-step explanation:
To determine how many σ (sigma) and π (pi) bonds are present in a given molecule, such as HCN, CO₂, and CO, it's important to understand the formation of these bonds. A sigma bond is typically formed when orbitals overlap in an end-to-end fashion, creating a single bond that allows for free rotation of atoms around the bond axis. In contrast, a pi bond is created by the side-to-side overlap of two p-orbitals, leading to areas of electron density above and below the nuclei plane, and is characteristic of multiple bonds such as double or triple bonds.
In the molecule HCN, which stands for hydrogen cyanide, there is a triple bond between the carbon (C) and nitrogen (N) atoms. This consists of one sigma bond and two pi bonds, due to the nature of triple bonds. Additionally, there is a sigma bond between the hydrogen (H) atom and the carbon (C) atom. Therefore, HCN has a total of two sigma bonds and two pi bonds.
For molecules like CO₂ (carbon dioxide), the carbon atom is double-bonded to each oxygen atom. Each double bond consists of one sigma and one pi bond. This results in a total of two sigma bonds and two pi bonds in CO₂. In the molecule CO (carbon monoxide), there is a triple bond between carbon and oxygen, similar to HCN, suggesting one sigma and two pi bonds, as well as a lone pair on the carbon.