Multiple Choice
Which of the following correctly represents the Lewis dot structure for a neutral molecule of HCl?
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11. Bonding & Molecular Structure
Lewis Dot Structures: Neutral Compounds
Multiple Choice
Which of the following Lewis dot structures correctly represents the covalent compound boron trichloride (BCl_3)?
A
A central B atom with three single bonds to three Cl atoms, each Cl atom having one lone pair, and the B atom having two lone pairs.
B
A central B atom with three single bonds to three Cl atoms, each Cl atom having two lone pairs, and the B atom having one lone pair.
C
A central B atom with three single bonds to three Cl atoms, each Cl atom having three lone pairs, and the B atom having no lone pairs.
D
A central B atom with three double bonds to three Cl atoms, each Cl atom having two lone pairs, and the B atom having no lone pairs.
Verified step by step guidance1
Step 1: Identify the total number of valence electrons available for bonding in BCl_3. Boron (B) has 3 valence electrons, and each chlorine (Cl) atom has 7 valence electrons. Since there are three Cl atoms, total valence electrons = 3 (from B) + 3 × 7 (from Cl) = 24 electrons.
Step 2: Determine the bonding framework. Boron is the central atom, and it forms bonds with the three chlorine atoms. Each bond is a pair of shared electrons (2 electrons per bond). For three single bonds, 3 × 2 = 6 electrons are used.
Step 3: Distribute the remaining electrons as lone pairs. After forming the three B–Cl single bonds, subtract the bonding electrons from the total valence electrons: 24 - 6 = 18 electrons left. These electrons are placed as lone pairs on the chlorine atoms to complete their octets. Each Cl needs 3 lone pairs (6 electrons) to reach 8 electrons total (2 from bond + 6 from lone pairs).
Step 4: Check the boron atom's electron count. Boron has only 3 bonds (6 electrons) and no lone pairs. Boron is an exception to the octet rule and is stable with 6 electrons in its valence shell in this molecule.
Step 5: Evaluate the given options based on the above reasoning. The correct Lewis structure has a central B atom with three single bonds to three Cl atoms, each Cl atom having three lone pairs, and the B atom having no lone pairs.
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