Inorganic and Applied Chemistry

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Inorganic and Applied Chemistry

Example 2- K:

The dinitrogen oxid molecule in Lewis structure

In the N 2 O molecule it is not so obvious which of the atoms that should be the central atom and how the

electrons shall be arranged in order to satisfy the octet rule for each atom. When the guidelines given in (2-

2) on page 59 are used you can reach the three Lewis structures given in Figure 2- 13a. In order to judge

which of these three structures are the most realistic, the formal charge of each atom has to be determined

according to (2- 3) on page 64. First the bond electrons are “shared” equally between the atoms as shown

in Figure 2- 13b. The number of electrons surrounding each atom is the counted. After that the number of

valence electrons for that element is then drawn from the number of surrounding electrons and you then

have the formal charge which is sketched in Figure 2- 13b. Since molecules normally seek to be as low in

energy as possible, it is advantageous for them overall to be in as low formal charge as possible. Thus the

most realistic of the Lewis structures given in Figure 2- 13a and b are the two upper ones. Thus the Lewis

structure for the N 2 O molecule can be considered as being a combination of the two structures given in

Figure 2- 13c.

Figure 2- 13 Lewis structure for the dinitrogen oxid molecule

(a) Three possible Lewis structures. (b) The formal charge is determined for all three atoms in the

molecule. (c) Lowest possible energy level is related with lowest possible formal charge for the single

atoms. The first two structures are therefore more realistic than the last structure. The Lewis structure for

the N 2 O molecule is thus considered as a combination of the two upper structures.

Chemical compounds