In the cyanate ion, OCN-, carbon is the central atom. (b) Which resonance structure makes the greatest contribution to the resonance hybrid? Which makes the least contribution? Explain.

Verified step by step guidance

1. Identify the possible resonance structures for the cyanate ion (OCN-). In each structure, consider different arrangements of double bonds and lone pairs while ensuring that the formal charges are minimized and the octet rule is satisfied for each atom.
2. Calculate the formal charge on each atom in every resonance structure. The formal charge can be calculated using the formula: Formal Charge = (Valence electrons) - (Non-bonding electrons) - 0.5*(Bonding electrons).
3. Assess the overall charge distribution in each resonance structure. Structures with formal charges closest to zero on each atom are generally more stable and contribute more to the resonance hybrid.
4. Evaluate the placement of negative charges in the resonance structures. Structures where the negative charge is located on the more electronegative atom (oxygen in this case) are typically more stable.
5. Determine which resonance structure has the most favorable characteristics based on the above evaluations. The structure with minimized formal charges, proper placement of the negative charge, and adherence to the octet rule will make the greatest contribution to the resonance hybrid. Conversely, the structure that least meets these criteria will make the least contribution.

Key Concepts

Resonance Structures

Resonance structures are different Lewis structures for a molecule that can be drawn by moving electrons around while keeping the positions of the atoms fixed. These structures represent the same molecule but differ in the distribution of electrons, particularly in the placement of double bonds and lone pairs. The actual structure of the molecule is a resonance hybrid, which is a weighted average of all valid resonance forms.

Formal Charge

Formal charge is a theoretical charge assigned to an atom in a molecule, calculated based on the number of valence electrons, the number of non-bonding electrons, and half the number of bonding electrons. It helps in determining the most stable resonance structure, as the structure with the lowest formal charges on atoms is generally more favorable. A formal charge of zero on all atoms is ideal, but if not possible, the negative charges should reside on the more electronegative atoms.

Electronegativity

Electronegativity is a measure of an atom's ability to attract and hold onto electrons in a chemical bond. In resonance structures, the placement of charges is influenced by electronegativity; more electronegative atoms are better suited to bear negative charges. Understanding electronegativity helps in evaluating which resonance structures are more stable and thus contribute more significantly to the resonance hybrid.