Why does O acquire a positive charge in the reaction

[andyrk]

The reaction is shown in the image attached. So the lone pair over O goes into making a bond with C. But why does it create a + over O? A + means the number of protons are one more than electrons, or deficiency of 1 electron. But if the lone pair is used up for making a bond, shouldn't it result into a 2+ charge and not just a single +?

 

[Borek]

You started with a cation, nothing has changed in terms of total number of protons of electrons - charge just shifted.

 

[andyrk]

Why did the charge shift?
The cation (i.e the carbon atom) in beginning had deficiency of 1 electron. That's why it had a + charge on it. But when it forms a bond with H, it gets back the electron that it was short on and also gets another electron (as H carried 2 electrons with it on its way to C+) so as to fully complete its octet. How is that C even related to O which not even directly connected to it?

 

[Borek]

As long as the molecule is isolated, its charge can't change (this is the charge conservation at work). The only thing that can change is the charge localization on the molecule. When the electrons move between bonds/atoms, charge shifts - but it doesn't change. So if you start with a +1 molecules, it stays at +1 as long as it doesn't loose or accept an electron.