GUIDELINES FOR DRAWING LEWIS STRUCTURES A Lewis structure consists of the electron distribution in a compound and the formal charge on each atom. You are expected to be able to draw such structures to represent the electronic structure of compounds. The following guidelines are given to assist you. 1. Determine whether the compound is covalent or ionic. If covalent, treat the entire molecule. If ionic, treat each ion separately. Learn to recognize complex ions. 2. Determine the total number of valence electrons available to the molecule or ion by (a) summing the valence electrons of all the atoms in the unit and (b) adding one electron for each net negative charge or subtracting one electron for each net positive charge. Then divide the total number of available electrons by 2 to obtain the number of electron pairs (EP) available. 3. Organize the atoms so there is a central atom (usually the least electronegative) surrounded by ligand (terminal) atoms or ligand groups. Note that hydrogen is always a ligand atom never a
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