Which of the following Lewis dot structures correctly represents the covalent compound boron trichloride (BCl_3)?

• A. Boron atom in the center with three double bonds to three chlorine atoms, each chlorine atom has two lone pairs, and boron has no lone pairs.
• B. Boron atom in the center with three single bonds to three chlorine atoms, each chlorine atom has two lone pairs, and boron has one lone pair.
• C. Boron atom in the center with three single bonds to three chlorine atoms, each chlorine atom has one lone pair, and boron has two lone pairs.
• D. Boron atom in the center with three single bonds to three chlorine atoms, each chlorine atom has three lone pairs, and boron has no lone pairs.

Answer: (D)

Verified step by step guidance

1. Step 1: Identify the total number of valence electrons available for bonding in BCl_3. Boron has 3 valence electrons, and each chlorine atom has 7 valence electrons. Since there are three chlorine atoms, total valence electrons = 3 (from B) + 3 × 7 (from Cl) = 24 electrons.
2. Step 2: Arrange the atoms with boron as the central atom and the three chlorine atoms surrounding it. This is because boron is less electronegative and typically forms the central atom in such compounds.
3. Step 3: Form single bonds between the boron atom and each chlorine atom. Each single bond consists of 2 electrons, so 3 single bonds use 6 electrons out of the total 24.
4. Step 4: Distribute the remaining electrons as lone pairs to satisfy the octet rule for the chlorine atoms. Each chlorine atom needs 8 electrons total (including bonding electrons), so after the single bond, each chlorine will have 6 electrons as lone pairs (3 lone pairs per chlorine).
5. Step 5: Check the boron atom's electron count. Boron often forms stable compounds with an incomplete octet, so it will have only 6 electrons (from the three single bonds) and no lone pairs. This matches the correct Lewis structure for BCl_3.