Rules for Writing Lewis Dot Structures for Molecules

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
(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.