Notes Ch 9 - Lewis Dot Structure Rules PDF

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Rules for Writing Lewis Dot Structures for Molecules 1. Sum valence electrons from all atoms

 It does not matter which atom they come from.  Add 1 e- for each (-) charge  Subtract 1 e- for each (+) charge 2. Identify the central and terminal atoms and write the skeletal structure

 The central atom will usually be one of the lowest electronegativity (H excepted)  This will sometimes be given or may take some trial and error. (H is always terminal) (O usually terminal except for peroxides and hydroxides OH) (C is always a central atom, it always has 4 bonds) 3. Draw a bond between each pair of atoms an appropriate.

 Each bond uses up 2 of the available e-. 4. Assign remaining e- to terminal elements first until duet rule has been met for H and octet rule has been met for all others. 5. If there are leftover e-, place them first on the central atoms to complete their octets. If there are additional e- still left, place them on central atoms that have empty d orbitals. 6. If all e- are used up and the central atoms do not have completed octets, move one or more lone pairs to form a multiple bond.

Note: If there is a choice (more than one arrangement of electrons will satisfy the requirements of items 5 and/or 6), choose based on the lowest formal charge....