Lewis Structure of Boron Trifluoride (BF3)

Boron trifluoride (BF₃) has a trigonal planar molecular geometry. Boron trifluoride consists of a boron atom single-bonded to three evenly spaced fluorine atoms in a trigonal planar arrangement. All three of its bonds are sigma bonds (overlapping orbitals of the two participating atoms).

Here’s how to draw its Lewis structure:

1. Count the total number of valence electrons:
   • Boron (B) has 3 valence electrons.
   • Fluorine (F) has 7 valence electrons and there are three Fluorine atoms.
   • Total electrons = 3 (from B) + 3 × 7 (from F) = 3 + 21 = 24 electrons.
2. Place the central atom:
   • Boron is the central atom since it is less electronegative than fluorine and can form multiple bonds.
3. Connect the atoms with single bonds:
   • Draw single bonds from Boron to each of the three Fluorine atoms. This uses up 6 electrons (2 for each bond).
4. Distribute the remaining electrons:
   • You now have 24 – 6 = 18 electrons left.
   • Place these electrons around the fluorine atoms to complete their octets. Each fluorine needs 6 more electrons (3 pairs), so:
     • 3 pairs on each F atom = 3 × 6 = 18 electrons.
5. Check the octet rule:
   • Each Fluorine now has 8 electrons around it (including the shared pair with Boron).
   • Boron, however, only has 6 electrons (3 bonds × 2 electrons each). This means Boron does not fulfill the octet rule, which is acceptable in this case because Boron can be stable with only 6 electrons around it in some compounds like BF₃.
6. Formal Charges:
   • To ensure this is the most stable structure, check formal charges:
     • For Boron: 3 (valence e-) – 0 (non-bonding e-) – 3 (bonds) = 0
     • For each Fluorine: 7 (valence e-) – 6 (non-bonding e-) – 1 (bond) = 0

Since all formal charges are zero, and this structure adheres to the lowest energy configuration, here’s how the Lewis structure looks:

• Each line represents a bond (2 electrons).
• Each Fluorine atom will also have three lone pairs of electrons, which aren’t typically shown in a simple Lewis structure drawing but are understood to be there to complete the octet.

Remember, while this structure shows the connectivity, BF₃ in reality has all bonds equal due to resonance and electron delocalization, although the simple Lewis structure doesn’t fully capture this phenomenon.