Revised: 2/12/15
A COMPUTATIONAL STUDY OF SCN-
REPORT INSTRUCTIONS
Create a computational study page in the Week 5’s folder. All Spartan files and tables for this
experiment must be attached to or in the ELN. No formal lab report sections are needed.
INTRODUCTION
Lewis structures are created by summing the valence electrons of all the atom’s of a chemical
species and then arranging those electrons so each atom typically has an octet of electrons. For
example, the Lewis structure of NO2- has a total of 18 valence electrons – 6 from both oxygen
atoms, 5 from the nitrogen atom, and 1 extra because of the negative charge.
When the Valence Shell Electron Pair Repulsion (VSEPR) theory is applied, the shape of the
chemical species can be determined. The lone pair of electrons on the nitrogen atom will result
in a bent molecule.
The placement of the double bond between the nitrogen atom and the oxygen on the right is
arbitrary.
When two or more Lewis structures differ only by the placement of double or triple bonds, they
are referred to as resonance structures. An imbalance of the number of lone and bonding pairs
around a particular atom can potentially create a charge localized on that atom. The charge on
that atom is referred to as formal charge and is calculated by the following equation:
Formal Charge = # of valence e-s – (# of lone pair e-s + ½ # of bonding pair e-s)
For the oxygen atom singly bound to the nitrogen atom above, the formal charge is calculated as
follows:
Formal Charge = 6 – (6 + ½ (2)) = -1
So, a more accurate representation of NO2- places the negative charge on the oxygen atom singly
bound to the nitrogen atom and shows both resonance structures.
O N O
-
O
N
O
-
O
N
O
-
-
O
N
O O
N
O
-
