Why is NH4+ an ionic species?

[20090900]

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So i tried googling it but I can't find out why. Can someone please explain, thanks!

 

[jefff]

NH4+ it is formed when NH3 reacts with an H+
(nitrogen has 1 lone pair of electrons)
(hydrogen ion has 0 electrons, but 1 proton)

*remember atoms are neutral when they have equal number of p+ and e-

~coordinate covalent bond is formed when H+ --bond--> :NH3 = NH4+

*in total there is 1 less electron than there are protons hence the + charge for NH4+

edit: also this may help for future
also know how to calculate formal charges

sum of the individual formal charges on each atom in a molecule = molecules total charge

formal charge = (# valance electrons) - (# of bonds) - (# of nonbonding electrons)

ex/ NH3
nitrogen formal charge = (5) - (3) - (2) = 0
hydrogen formal charge = (1) - (1) - (0) = 0
hydrogen formal charge = (1) - (1) - (0) = 0
hydrogen formal charge = (1) - (1) - (0) = 0
NH3 total charge = 0 - 0 - 0 - 0 = 0

ex/NH4
nitrogen formal charge = (5) - (4) - (0) = +1
hydrogen formal charge = (1) - (1) - (0) = 0
hydrogen formal charge = (1) - (1) - (0) = 0
hydrogen formal charge = (1) - (1) - (0) = 0
hydrogen formal charge = (1) - (1) - (0) = 0
NH4 total charge = +1 - 0 - 0 - 0 - 0 = +1

 

[Dusk]

Just memorize the few polyatomic ions that always appear in the dat. NH4+, NO3-, phosphate, sulfate, etc.

 

[20090900]

ok thanks. quick question: when calculating formal charge, does a double/triple bond count as just one bond or 2/3 bonds respectively?

 

[jefff]

single bond is 1 bond
double bond is 2 bonds
triple bond is 3 bonds

if you've seen other formulae for calculating formal charge, this portion of the calculation is sometimes stated as (½ # of bonding electrons)

a single bond has 2 bonding electrons and therefore ½(2) = 1
a double bond has 4 bonding electrons and therefore ½(4) = 2
a triple bond has 6 bonding electrons and therefore ½(6) = 3

so hopefully that will help you visualize its easiest to just use:
formal charge = (# valance electrons) - (# of bonds) - (# of nonbonding electrons)

 

[Dotoday]

anything that has a charge isconsidered an ion. Nitrogen with 4 bonds has +1 charge. Oxygen with 3 bonds has +1 charge, oxygen with 1 bond has -1 charge.