In coordinate bond, why doesn't the H^+ atom get a negative charge?

[mjc123]

Protons attract electrons by charge, not mass. The electrical force is enormously greater than the gravitational force between electrons and protons - a factor of about 10³⁹.

 

[HCverma]

'

It will also get 3 protons (in the case of NH₃) or 4 protons (in the case of NH₄⁺). For simplicity, in the case of NH₃, N will share 3 of its electrons with 3 hydrogen atoms (each with 1 electron and 1 proton). It doesn't take the hydrogens' electrons from them (at least not entirely--see below). If it did, then you would write ammonia's formula as N^3-(H⁺)₃. Covalent bonds involve sharing of electrons. The 3 electrons from the hydrogens serve to complete the nitrogen's octet, but they don't count toward the formal charge. For the formal charge, each covalent bond counts as one electron.

So for NH₄⁺, there are 4 covalent bonds around nitrogen; therefore there are 8 (4x2) valence electrons satisfying the nitrogen's octet, but only 4 valence electrons counting toward nitrogen's formal charge. Add the 2 non-bonding 1s electrons and you have 6 total electrons assigned to nitrogen for the sake of formal charge. Since nitrogen has 7 protons, the formal charge on nitrogen is +1.

(Caveat: there is some polarity in the N-H bond. That is, a given electron is more likely to be found around the nitrogen in an N-H bond than the hydrogen. However, it is far from being a complete charge transfer.)

I understand everything except this point 'Add the 2 non-bonding 1s electrons and you have 6 total electrons assigned to nitrogen for the sake of formal charge.' Add to which atom the 2 non-bonding 1 s electrons? Could you simplify your point, please?

 

[TeethWhitener]

Add to which atom the 2 non-bonding 1 s electrons?

No, add as in 4+2=6. You have 4 electrons from nitrogen participating in bonding in NH₄⁺. You have 2 electrons in the 1s orbital of nitrogen (these electrons are not valence electrons: they don't participate in bonding). You add 4+2 to get 6 electrons assigned to nitrogen. Since nitrogen has 7 protons (this is always true--otherwise it's not nitrogen), its formal charge is 7-6 = +1.