Finding Lone Pairs That Are Not Drawn

From all of the cases above (oxygen, nitrogen, carbon), you can see why you have to know how many lone pairs there are to figure out the formal charge on an atom. Similarly, you have to know the formal charge to figure out how many lone pairs there are on an atom. Take the case below with the nitrogen atom showm  

So you can see that drawings must include either lone pairs or formal charges. The convention is to ahvays show formal charges and to leave out the lone pairs. This is much easier to draw, because you usually won t have more than one charge on a drawing (if even that), so you get to save time by not drawing every lone pair on every atom. 

Now that we have established that formal charges must always be drawn and that lone pairs are usually not drawn, we need to get practice in how to see the lone pairs when they are not drawn. This is not much different from training yourself to see all the hydrogen atoms in a bond-line drawing even though they are not drawn. If you know how to count, then you should be able to figure out how many lone pairs are on an atom where the lone pairs are not drawn. 

Tlie oxygen has one bond, which means that it is using one of its seven electrons to form a bond. The other six must be in lone pairs. Since each lone pair is two electrons, this must mean that there are three lone pairs  

Count the number of electrons the atom should have according to the periodic table. 

Take the formal charge into account. A negative charge means one more electron, and a positive charge means one less electron. 

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If the two lone pair sp orbitals on oxygen are drawn in the customary skittle shapes, the major lobes in a Newman projection look like two rabbit s ears. The direct electrostatic effect of lone pair electrons was therefore dubbed the rabbits ears effect, but failed to find acceptance, as much from the overtones of Beatrix Potter as from the fact that the shape of electron density resembled not two, but one ear (Figure 2.11). 

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