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RelativeResourceManager-1 - Drawing Lewis Structures 1...

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Drawing Lewis Structures 1 Determine the total number of valence electrons for ALL atoms. Don’t be concerned with which atom gave what; the SUM TOTAL is what is important. If the entire molecule is charged (i.e. a polyatomic anion or cation) add one valence electron for each unit of negative charge (if it is an anion) and remove one valence electron for each unit of positive charge (if it is a cation). 2 Write a skeleton structure for the molecule, making the least electronegative atom the central atom. The order of electronegativity for the nonmetals is F>O>N>Cl>Br>I>S>C>H. Metals will almost always be the central atom if they are present. Hydrogen is never the central atom. a If there are more than one of the least electronegative atom, your skeletal structure should have those two attached to one another (EXCEPTION: Hydrogen) 3 Connect each member of the skeleton structure to the central atom(s) using a single line to represent a bond. Each bond is comprised of two electrons so each line indicates a two- electron bond (two and only two electrons). 4 Count the number of bonds that you made in step 3 and multiply that by 2. Subtract that number from the number of total valence electrons from step 1. This is the number of electrons you have left to distribute. Simply: you are counting the electrons you have used and subtracting from what you started with to find out how many you have left ! This is a tally you must always be aware of.
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5 Starting with the atoms bonded TO the central atom (the ‘outside’ atoms), distribute the electrons two at a time until all electrons from step 4 are used OR until each atom has an octet (eight electrons around it); DO NOT give hydrogen any of these ‘left-over’ electrons. A good rule of thumb is to give EACH non-hydrogen two electrons at a time until each outside atom has two extras, then give two more to each non-hydrogen until each has four extra electrons and so on. Once all of the ‘outside’ atoms have octets (except for the hydrogens), put remaining electrons on the central atom(s) until all electrons are used or every atom has an octet (or a duet, in the case of H). . AT THIS POINT: Any time
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RelativeResourceManager-1 - Drawing Lewis Structures 1...

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