Multiple Choice
Which of the following is the correct Lewis dot structure for chloroethylene (C2H3Cl)?
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11. Bonding & Molecular Structure
Lewis Dot Structures: Neutral Compounds
Multiple Choice
Which of the following is the correct Lewis dot structure for boron trichloride (BCl_3)?
A
B atom in the center with three double bonds to Cl atoms; each Cl atom has two lone pairs; B has no lone pairs.
B
B atom in the center with three single bonds to Cl atoms; each Cl atom has three lone pairs; B has no lone pairs.
C
B atom in the center with three single bonds to Cl atoms; each Cl atom has two lone pairs; B has one lone pair.
D
B atom in the center with three single bonds to Cl atoms; each Cl atom has one lone pair; B has two lone pairs.
Verified step by step guidance1
Step 1: Identify the total number of valence electrons available for bonding. 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 because it is less electronegative than chlorine. Connect the boron atom to each chlorine atom with a single bond initially. Each single bond represents 2 electrons.
Step 3: Distribute the remaining electrons as lone pairs on the chlorine atoms to complete their octets. Each Cl atom needs 8 electrons total (including bonding electrons). Since each Cl is bonded with one single bond (2 electrons), add 6 electrons (3 lone pairs) to each Cl atom.
Step 4: Check the boron atom's electron count. Boron is an exception to the octet rule and is stable with 6 electrons around it (3 single bonds × 2 electrons each). Therefore, boron has no lone pairs and does not form double bonds in BCl₃.
Step 5: Confirm the Lewis structure: Boron in the center with three single bonds to chlorine atoms; each chlorine atom has three lone pairs; boron has no lone pairs. This matches the correct Lewis dot structure for BCl₃.
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