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Why does the molecule have net positive charge? enter image description here

quantised
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    Because the particles before the formation of the said bond had a net charge. – Ivan Neretin Jul 13 '18 at 13:13
  • why not negative charge then? – quantised Jul 13 '18 at 14:17
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    Because they never had negative charge in the first place. – Ivan Neretin Jul 13 '18 at 14:38
  • shouldn't positive charge of H get neutralised when it gets an electron? Also, what are the criteria for getting the total charge of the compound? Is it by adding formal charges? What is the formal charge of O after forming the coordinate bond? – quantised Jul 13 '18 at 15:01
  • It never gets an electron for free. Instead, it starts to share someone else's electrons. – Ivan Neretin Jul 13 '18 at 15:04
  • Before you know a thing about formal charges, and even before you know a thing about atoms, you have to know that the total charge is always conserved. Now the total charge of $\ce{H2O}$ is 0, and the total charge of $\ce{H+}$ is +1 (we know that because it is written with that little $^+$). Just what their combined total charge might be? – Ivan Neretin Jul 13 '18 at 15:08
  • +1, so every time a compound ionizes, is it because of coordinate bond? – quantised Jul 13 '18 at 15:16
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    No, this is not because of coordinate bond. The charge is conserved no matter what. Coordinate bonds are irrelevant here, as well as bonds of any other type. – Ivan Neretin Jul 13 '18 at 15:51
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    @IvanNeretin I have feeling this is hopeless case here... – Mithoron Jul 13 '18 at 16:25
  • @IvanNeretin I finally understood it :) Thanks for your patience – quantised Jul 13 '18 at 16:54

2 Answers2

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Consider the formation of the given hydronium ion: $\ce{H2O + H+ -> H3O+}$ (also more correctly stated as the auto-ionization of water: $\ce{2H2O -> H3O+ + OH-}$)

The positive charge you're seeing indeed belongs to the whole molecule, as any reaction conserves charge both on the left and right side of the arrow.

However, this is not true in general. If a neutral molecule itself forms from neutral atoms, which involves a coordinate bond, then the molecule won't be charged.

Although, do note that the distinction between normal covalent bond and coordinate covalent bonds is artificial.

Gaurang Tandon
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The charges are produced only due to the nearness of the electrons with the nucleus of the respective atom. Here the co-ordinate bonds produces charge because the electrons in this case is near the H atom which results in a partial positive charge on H that's why there is a charge overall in the compound.

Utsav Umang
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