[deutdeut]

Suppose in a chlorine molecule, each chlorine atom attain the stable electonic configuration after the electrons are shared. Each chlorine atom then has 8 outermost shell electrons. Then, the two chlorine atoms become two chloride ions?

[Donaldson Tan]

Then, the two chlorine atoms become two chloride ions?

Covalent bonding is a type of chemical bonding that is characterised by the sharing of one or more electrons between two atoms. You have Cl-Cl and not 2 chloride atoms. Each chlorine atom donates an electron to the covalent bond and shares the electron pair in the covalent bond, so each chlorine atom has 8 electrons in its valence shell after bonding.

[deutdeut]

How about the net charge on each Cl atom?

[english]

How about the net charge on each Cl atom?

Diatomic chlorine has a formal charge of 0.  Formal charge is the charge the chlorine atom has as it would if it shared valence electrons equally.  In this case, chlorine exists in a nonpolar form, so the valence electrons are shared equally.

General formula for formal charge is:

# of valence electrons - (1/2*number of bonding electrons + number of lone pair electrons)

[deutdeut]

I mean, since the Cl atom has 17 protons but 18 electrons, does the charge is 1- ?

[Borek]

I mean, since the Cl atom has 17 protons but 18 electrons, does the charge is 1- ?

How did you get to the conclusion that it has 18 electrons?

[deutdeut]

Because of the sharing of electrons, it should have 18 electrons, right?

[Borek]

Because of the sharing of electrons, it should have 18 electrons, right?

How many electrons will the second atom in the molecule have then?

[deutdeut]

Also 18

[Borek]

Total of 36? Where do the two new electrons come from?

[deutdeut]

I mean, the 18 electrons include the  2 same bonded electrons. If I just view only ONE atom in chlorine molecule, the charge on Cl will be 1-, because there are 17 protons and 18 electrons. But that is not possible, for sure. So, I am confused about it!!!

[english]

Each chlorine atom in diatomic chlorine has a net charge of 0, not -1.  Each atom does have 17 protons, and 18 electrons in the molecule.

The molecule is not polar though.  Since both of your atoms are identical, neither pulls harder than the other on the valence electrons. 

Remember what I said of formal charge earlier:

General formula for formal charge is:

# of valence electrons - (1/2*number of bonding electrons + number of lone pair electrons)

[deutdeut]

Why should I use the so-called formal charge? After sharing, shouldn't each Cl atom has 18 electrons, including the bond pair electrons?

[Borek]

I mean, the 18 electrons include the  2 same bonded electrons. If I just view only ONE atom in chlorine molecule, the charge on Cl will be 1-, because there are 17 protons and 18 electrons. But that is not possible, for sure. So, I am confused about it!!!

You are assuming that one atom has 17 protons and 18 electrons, and it leads to impossible conclusions - so perhaps you should rethink your assumption? Perhaps every atom 'has' 17 electrons?

[deutdeut]

But in the chlorine molecule, each atoms should have an octet structure?