Question

what is the correct structure for bf₃ ?

Explanation:

Step1: Determine Valence Electrons

Boron (B) has 3 valence electrons, and each Fluorine (F) has 7. For \( \text{BF}_3 \), total valence electrons: \( 3 + 3\times7 = 24 \).

Step2: Analyze Bonding and Lone Pairs

Boron is the central atom. It forms single bonds with 3 F atoms (each single bond uses 2 electrons). Each F atom has 3 lone pairs (6 electrons) to satisfy octet. Let's check each option:

• First Option: B has 3 single bonds (6 electrons), each F has 3 lone pairs (6 electrons). Total electrons: \( 3\times2 + 3\times(2 + 6) = 6 + 24 = 30 \)? Wait, no—wait, each single bond is 2 electrons (B - F), and each F has 6 lone electrons. Wait, B has 3 valence electrons, so 3 single bonds (each F contributes 1 electron to bond, B contributes 1). So B's electrons: 3 bonds (6 electrons), but B has 3 valence, so that's okay (boron can have incomplete octet here). Each F: 1 bond (2 electrons) + 6 lone = 8, good. Total electrons: \( 3\times2 + 3\times6 = 6 + 18 = 24 \), which matches.
• Second Option: Double bonds. B would have more electrons, but B only has 3 valence, can't form double bonds (would require more electrons than available).
• Third Option: Incorrect structure (F - F bonds, not B - F as central).
• Fourth Option: B has a lone pair? B only has 3 valence, can't have a lone pair (would exceed 3). So first option is correct.

Answer:

The first structure (with B bonded to three F atoms via single bonds, each F having three lone pairs of electrons).