Final answer:
The carbon atom in the cyanide ion (CN-) has a partial positive charge due to the electronegativity difference with nitrogen, which holds a partial negative charge. A triple bond between the two atoms is responsible for this charge distribution, similar to polar covalent bonds seen in other molecules like HCl.
Step-by-step explanation:
To determine the partial charge on the carbon atom in the cyanide ion (CN-), we consider its electronic structure and distribution. The CN- ion has a total of 10 valence electrons: 4 from carbon (C) and 5 from nitrogen (N), plus an extra electron due to the -1 charge on the ion. These electrons will fill up the lowest-energy orbitals, forming a triple bond between C and N, analogous to the triple bond in dinitrogen (N₂). The bond order, which can be predicted as (8 - 2) ÷ 2 = 3, supports the presence of this triple bond.
Nitrogen is more electronegative than carbon, which leads to a partial negative charge on the nitrogen atom. Since the bonding electrons are more attracted towards nitrogen, this results in a partial positive charge on the carbon atom due to the electron distribution favoring nitrogen. For comparison, in an HCl molecule, we can measure the partial charges using the dipole moment and bond length. The electron distribution here is also asymmetric, resulting in a partial negative charge on the chlorine atom of about -0.18.
The partial charge on nitrogen in the CN ion implies a corresponding partial positive charge on the carbon, typically less than +1, as the bond is covalent with polar characteristics rather than purely ionic.