Lewis Acid-Base: Is BH3 a Base?

[terryds]

Homework Statement

In the reaction with NH₃, is specy BH₃ a Lewis base ?

Homework Equations

Lewis acid = electron acceptor
Lewis base = electron donor

The Attempt at a Solution

H electronegativity = 2.1
B electronegativity = 2.0
N electronegativity = 3
Since N-H bond is more electronegative than B-H bond, NH₃ is more electronegative than BH₃ which means that NH3 is more easily to accept electron. So, NH₃ is Lewis acid, BH₃ is Lewis base

Is it correct??
My book says that NH₃ is the base with no reason, and I doubt that.

 

[sidt36]

A good way to analyse the above problem would be to draw the Lewis structures.There is a reason it is named after G.N. Lewis!

 

[terryds]

A good way to analyse the above problem would be to draw the Lewis structures.There is a reason it is named after G.N. Lewis!

Alright,
Based on Lewis structure, NH₃ have three pair of bonding electrons and one pair of free electrons while BF₃ have three pair of bonding electrons.

and then? How to determine which one is base or acid ?

 

[sidt36]

So the electron configuration is something like this

So i think this might help

 

[sidt36]

My teacher Told me if it has an empty orbital ->Lewis acid
Otherwise its most likely ->Lewis base

 

[terryds]

Thanks! I got it!