Which of the following is the correct formula unit for the ionic compound formed when calcium combines with nitrogen?

• A. CaN_2
• B. Ca_3N_2
• C. CaN
• D. Ca_2N

Answer: (B)

Verified step by step guidance

1. Identify the charges of the ions formed by calcium and nitrogen. Calcium is in Group 2 and typically forms a Ca^{2+} ion, while nitrogen is in Group 15 and typically forms an N^{3-} ion.
2. Determine the ratio of calcium ions to nitrogen ions needed to balance the total positive and negative charges so that the compound is electrically neutral.
3. Set up the charge balance equation: let the number of calcium ions be x and the number of nitrogen ions be y. The total positive charge is 2x and the total negative charge is 3y. For neutrality, 2x = 3y.
4. Find the smallest whole number ratio of x to y that satisfies 2x = 3y. This ratio will give the subscripts in the formula unit of the ionic compound.
5. Write the formula unit using the ratio found, placing the calcium subscript first followed by the nitrogen subscript, resulting in the correct formula unit for the compound.