How the Structure of a Compound Is Represented

First we will see how compounds are drawn using Lewis structures. Then we will look at the kinds of structures that are used more commonly for organic compotmds. 

The chemical symbols we have been using, in which the valence electrons are represented as dots or solid lines, are called Lewis structures. Lewis structures show us which atoms are bonded together and tell us whether any atoms possess lone-pair electrons 

Notice that the atoms in Lewis structures are always lined up linearly or at right angles. Therefore, they do not tell us anything about the bond angles in the actual molecule. 

When you draw a Lewis stmcture, make sure that hydrogen atoms are surrounded by two electrons and that C, O, N, and halogen (F, Cl, Br, 1) atoms are surrounded by eight electrons, in accordance with the octet rule. Valence electrons not used in bonding are called nonbonding electrons or lone-pair electrons. 

Once you have the atoms and the electrons in place, you must examine each atom to see whether a formal charge should be assigned to it. A formal charge is the difference between the number of valence electrons an atom has when it is not bonded to any other atoms and the number it owns when it is bonded. An atom owns all of its lone-pair electrons and half of its bonding (shared) electrons. 

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