Final answer:
The formal charge on the nitrogen atom in hydrogen cyanide (HCN) can be calculated to be +1, based on the number of valence electrons, lone pairs, and bonding electrons, despite some initial confusion with the application of the formal charge formula.
Step-by-step explanation:
The formal charge on an atom in a molecule can be calculated using the following formula: Formal charge = (number of valence electrons on the free atom) - (number of lone pair electrons) - (1/2 * number of bonding electrons). For the nitrogen atom in hydrogen cyanide (HCN), nitrogen normally has 5 valence electrons. In the Lewis structure for HCN, nitrogen forms three bonds (one triple bond to carbon and no lone pairs). So, following our formula, the formal charge would be 5 - (0 lone pair electrons) - (1/2 * 6 bonding electrons) = 5 - 3 = +2. This clearly indicates some error since we are expecting formal charge values like -1, 0, or +1, typically.
However, based on common formal charges and known resonance structures, nitrogen in HCN often possesses a lone pair, with a triple bond to the carbon atom, and the hydrogen is bonded to carbon. Therefore, the formal charge calculation should be adjusted as nitrogen should have a lone pair. With this in mind, nitrogen would have 5 valence electrons - (1 lone pair * 2 electrons) - (1/2 * 4 electrons from the triple bond) = 5 - 2 - 2 = +1, which matches the information provided that in a Lewis structure, nitrogen has a +1 nearby. The formal charge on nitrogen in HCN is therefore +1.