Chemical Bonding: BH₃ Lewis Structure

Drawing the Lewis Structure for BH₃

Viewing Notes:

• The BH₃ Lewis structure is similar to BF₃, BCl₃ and BBr₃ since F, Cl, and Br are all in Group 7 and have 7 valence electrons.
• Boron (B) doesn't need 8 valence electrons to have an octet (Boron often only needs 6).
• If you're not sure you have the best Lewis structure for BH₃ you can calculate the formal charges. You'll find the B in BH₃ only has 6 valence electrons.
• For the BH₃ Lewis structure there are a total of 6 valence electrons available.

Transcript: Dr. B. here. Let's do the Lewis structure for BH3. On the periodic table, Boron's in group 3. It has 3 valence electrons. Hydrogen's in group 1, but we have 3 Hydrogens; so we have a total of 3 + 3: 6 valence electrons. Boron goes in the center, Hydrogens on the outside. So we'll put electrons in pairs between the atoms to form chemical bonds, and we've actually used all 6 already. Each Hydrogen has 2, so its outer shell is full. The Boron in the center only has 6 and we've used all of our valence electrons. Boron's actually OK with 6 valence electrons. If we were concerned, we could calculate the formal charges for each atom to see if they were zero. In this case, they are.

So this makes it the correct structure for BH3. This is Dr. B., and thanks for watching.