Which of the following is not a Lewis base?

Question

This was one of the questions from AP chem final exam in my class..

which of the following is not a Lewis base?

1. NH2 ( i can't remember the charge,,,)
2. NH3 (no charge)
3. NH4 (+)
4. Cl (-)

Lewis base, by definition, is a substance that can form cobalent bond by donating an electron pair to another substance.

Answer 1

Ans is NH4+
Lewis base is that substance which can form co-ordinate covalent bond donating a pair of electrons.NH2-, NH3 and Cl- have 2,1 and 4 electrone lone pair which they can easyly donate and thats why they are lewis base. But for NH4+ there is no lone pair in bonding orbital( 1S electrons of N is core inner shell e- thets why nitrogen cant donate it).Thats why it is not a lewis base

Answer 2

Don't take this as gospel, but I think its the ammonium ion (NH4+). The hydrogens only have the two electons of the bond between it and the nitrogen (they have no filled octet, so no extra pairs to donate) The nitrogen's electrons are all being used for the 4 bonds to hydrogen)

Answer 3

NH4(+)

Answer 4

NH3