# Why is it O-Cl-O and not O-O-Cl?

I'm currently preparing my exam and while I did never think about this question during the course, it begins to confuse me right now...

Why is it the structure of $\ce {ClO_{2}-}$ like $\ce {O-Cl-O}$ and not like $\ce {O-O-Cl}$?

I know how to place the covalent bonds and the electrons, but I don't know how to figure out the basic structure of the molecule. Is there a relatively simple rule to solve (and understand) such relatively simple molecules?

Is there a relatively simple rule to solve (and understand) such relatively simple molecules?

The most electropositive atom is usually at the center of a molecule because

• a "central atom" implies that there are multiple (more than 1) bonds to the central atom. If the central atom is relatively electropositive, then it will be better able to share its electrons and form bonds with other atoms, at least more so than an electronegative central atom would.
• electronegative atoms tend to carry multiple lone pairs of electrons. If this electronegative atom and all of its lone pairs were at the center of the molecular structure, then we would have many more destabilizing (lone-pair - bonding pair) electron-electron repulsions, then if all of these lone pairs were on the periphery of the molecule.

Try to draw the structure of $\ce{ClO2-}$. It will like this :

If you see the structure it is $\ce{O−Cl−O}$ and not $\ce{O−O−Cl}$.

Chlorine is in the center because Least electronegative atom will be at center. You can refer this links: YouTube and chemistry education

• The right O and Cl are connected by a covalent double bond? But Cl would then have 5 electron pairs which is wrong. (Furthermore, my textbook says, that the atoms are connected by single bonds only.) – Michael Aug 12 '14 at 18:45
• @Michael this is $\ce{ClO2-}$ Lewis Structure, if you want to know how to draw structure you should see this video. – Freddy Aug 12 '14 at 18:53
• Doesn't $O-O-Cl$ have lower formal charges than $O-Cl=O$? Why is having Chlorine as the central atom preferable to having oxygen as it? – 1110101001 Aug 12 '14 at 19:10
• @user2612743 Least electronegative atom will be at center. – Freddy Aug 12 '14 at 19:18
• @Freddy Why is it the least electronegative? Is it most conducive to "sharing" electrons/forming bonds? – 1110101001 Aug 12 '14 at 19:26
1. Draw a Lewis structure.
2. Check for formal charges. The structure which:

a. Has the less number of formal charges

b. Has the lowest charges sum (but appropriate to the molecule ionization state).

Will be more "natural" to occur.

For counting charges use: (Valance shell electrons)-(number of bonds near the atom)-(lone paired electrons)

where "-" stands for subtraction.

Edit: Didn`t notice her the lewis structure rules - suppose you are familiar with them.

• I'm having a hard time trying to see the novelty in this answer. Pretty much all that's written here has been covered by an accepted answer already. – andselisk Jan 23 '18 at 0:32
• Please dont try hard to search the novelty her, i just saw a familiar question and 1st time answered a random topic. Which after a while i noticed that it was very old :) – Mabadai Jan 23 '18 at 13:09