MOLECULE LEWIS DIAGRAMS
A Lewis diagram depicts a mmolecule using an element symbol
to represent the nucleus and core electrons of each atom. Valence
electrons are represented by lines for electron pair bonds and
dots for unbonded electrons.
The following procedure can be followed to derive Lewis diagrams
for most molecules.
1. Find the total number of electrons:
Tabulate the total number of outer energy level electrons for
all atoms in the molecule. For each atom, read the group number.
2. Draw a first tentative structure:
The element with the least number of atoms is usually the central
element. Draw a tentative molecular and electron arrangement
attaching other atoms with single bonds as the first guess. Single
bonds represented with a line represent 2 electrons
3. Add electrons as dots to get octets around atoms:
When counting electrons for the octet around an atom, count both
electrons in a bond for each atom and any lone pair electrons.
Hydrogen, of course, gets only 2 electrons.
4. Count the total number of electrons in the final structure
to see if the total agrees with the number tabulated in step
#1. If not, then move a lone pair of electrons into a double
bond. Or add more lone pairs of electrons.
5. Cycle through steps 3 and 4 several times until
you get it right by trial and error.