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.
