Drawing Lewis structure

[popcorn]

Would someone help in the following:-

1) draw lewis structure of odd electron molecules or atoms.

2) how to decide when there is going to be double or a co_ordinate bond?

(had this doubt while trying to draw the structure of S2O3(2-))

3) how to claculate formal charge and oxidation number in general and a

co_ordinate bond is involved in particular?

 

THANK YOU IN ADVANCE.....

[drufae]

q1) you can draw them the same way you draw normal systems just show the single pair.

q2)sorry don't know

q3)there are 2 ways .1 by assuming each atom in the molecule will have the same oxidation staet creating an equation and solving for your element(this only works in simple situations).

the 2nd ways is by looking at the structure of the molecule.if the bond is ionic the more electronegetive gets a full -1 charge added to its oxidation state,if between the 2 atoms participating in the bond one is more electropositive it gets +1 added.in case of co-valent bonds the same concept applies eevn though the electrotrons are not completely transferred.(you can think of it as heterolytic fission of all covalent bond before calculating the O.N.).As for co ordinate bonds There is absolutely no differnece in co valent and coordinate bonds after their formation.therefore if the bond is natural i.e. form an general electron donor to an general electron acceptor it is counted and a chage of 2( sign depends on atom) is added.if the opposite happens the bond is completely disregarded while calculating the O.N.

[Branos]

Q2) When the doubt between a co-ordinate and a double bound happens, there's always a chalcogen involved as a peripheral atom. In this case, there are 3, 2 O's and a S.

So that's the hint: First, complete the octet of the central atom with double bonds. Than, all the other bonds will be co-ordinate. In the ion thiosulfate, one sulfur is the central atom and the other is a peripheral atom. The central atom makes a double bond with an oxygen. With it, it's octet is complete, therefore, all the others bonds will be co-ordinate. However, because there is more than one bond with oxygen, there will be a resonance in the molecule. So, the following lewis structure is just a representation of one of the canonic forms of the ion:

Edited October 13, 2008 by Branos