Explain why NH3 reacts with alkyl halides not with NH4+?

Question

PLEASE HELP ME!!!!!!!!!!!!!!!!!!!!!!

Answer 1

NH3 has a lone pair of electrons, which it uses to attack the C atom which is bonded to the halogen atom. This is called nucleophilic attack. The ammonium ion doesn't have a lone pair of electrons, so it can't attack in this way.

Answer 2

Lancenigo di Villorba (TV), Italy

FUNDAMENTs
As you know, the AMMONIA's molecule (e.g. NH3) obeys to a TETRAHEDRON MODEL where Nitrogen Atom in Ammonia binds three Hydrogen Atoms by means of three Covalent Bonds and the related Electron's Atomic Orbitals ; Nitrogen Atom shows a FOURTH ORBITAL which hosts ITS OWN ELECTRON DUET.
This Duet is responsible for the BASICITY NATURE of Ammonia, e.g. you have to apply the ACID-BASE's THEORY developed by G. LEWIS, an american chemist.
As Lewis thought, Ammonia may SHARE ITS OWN Electron's Duet to get it in favour of several other Chemical Compounds, e.g. the Electrophilic Stuffs.

ABOUT AMMONIUM ION
Ammonium Ion (e.g. NH4+) is a ACID-BASE's PRODUCT from Ammonia : you may name it as AMMONIA's SALT.
On the other terms, Ammonium Ion derives from
ACID-BASE's REACTION occuring between Ammonia and Hydrogen Ion.
Moreover, Ammonium Ion haven't till Electron-Duet and it cannot acts as Electron-Donor

NH4+ + R-X ---> There's No Lewis-Reaction

where R-X is Alkyl Halides as I wrote here below.
Furthermore, Ammonium Ion haven't till Molecular Orbitals so it cannot host other Electron's Valence and it cannot acts as Electron-Acceptor

NH4+ + NH3 ---> There's No Lewis-Reaction.

ABOUT ALKYL HALIDEs
Alkyl Halides may results Excellent Electrophilic Stuffs.
In effects, their Molecular Structure are characterized by an Halogen Atom bound to the Molecule's Carbon-Chain.
The Carbon Atom binding the Halogen's One shows an influenced chemical behaviour since THEIR COVALENT BOND results a POLAR ONE.
The Carbon Atom in discussion becomes the Electrophilic Site WHERE THE ELECTRON-DONOR ARE MOVING ON.
Ammonia usually have success in reaction against Alkyl Halides

NH3 + R-X ---> R-NH3+ + X- As a Lewis-Reaction.

I hope this could be clear.