Which of the following is the correct chemical formula for barium phosphide?

• A. BaP2
• B. Ba2P3
• C. Ba2P
• D. Ba3P2

Answer: (D)

Verified step by step guidance

1. Step 1: Identify the charges of the ions involved. Barium (Ba) is an alkaline earth metal in Group 2, so it forms a cation with a charge of +2, written as Ba^{2+}. Phosphide is the anion formed from phosphorus, which gains three electrons to form P^{3-}.
2. Step 2: Determine the ratio of Ba^{2+} to P^{3-} ions needed to balance the overall charge to zero. Since Ba has a +2 charge and P has a -3 charge, find the smallest whole number ratio where the total positive charge equals the total negative charge.
3. Step 3: Use the least common multiple (LCM) of the charges 2 and 3 to find the total charge balance. The LCM of 2 and 3 is 6, so the total positive charge should be +6 and the total negative charge should be -6.
4. Step 4: Calculate the number of each ion needed to reach the total charge of 6. For Ba^{2+}, 3 ions are needed (3 × +2 = +6). For P^{3-}, 2 ions are needed (2 × -3 = -6).
5. Step 5: Write the chemical formula by combining the ions in the ratio found: 3 barium ions and 2 phosphide ions, resulting in the formula Ba_{3}P_{2}.