Drawing Lewis Dot Structures:
1.
Determine the central atom.

Most compounds are symmetrical. For example, if there is one “C” and two “O” like
in carbon dioxide, C will be the central atom.

If there is one of each, like in NOCl, the atom that can “make the most bonds”
should be placed in the center.
C: has 4 valence electrons – can make 4 bonds (to fill its octet) 4+4=8
N: has 5 valence electrons – can make 3 bonds, 5+3=8
O: has 6 valence electrons – can make 2 bonds, 6+2 =8
H and the halogens (F, Cl, Br, I) – can make 1 bond

H has one valence electron and is full with 2 (like He)

the halogens have seven valence electrons, 7+1=8
What would be the central atom in NOCl? _____
2. To determine the number of “dots”, add the number of valence electrons in each atom. Add
for each negative charge and subtract one for each positive charge. Lewis dot structures
for ions will have to be in brackets with the charge on the outside.

Examples: Determine how many valence electrons there are in each of the following:
a.
water (H2O)
b. ammonia (NH3)
c.
ammonium ion (NH4+)
d. sulfate ion (SO42-)
3.
Place them around to central atom to give it an octet, then fill in the octet for the
surrounding atoms. If there are not enough electrons for each atom to have an octet, make
a double or triple bond. (see e and f below)
 Example: methane (CH4)
 Calculate valence electrons: 4 from C, 1 from each H: 4+1+1+1+1 = 8
 Draw Lewis Dot Diagram for CH4
4. Practice: Draw Lewis Dot structures for
a.
NH3
e.
NOCl
2-
f.
N2
b. NH4
c.
SO4
d. F2
+