Chemistry
NAME:
§06.02a
DATE:
Steps for Drawing Lewis Structures
Example: NH3 (ammonia)
Steps
1. Determine the type and number of atoms in
the molecule.
Description
The formula shows one carbon atom, one
iodine atom, and three hydrogen atoms.
Example
Write the electron-dot notation for each type of atom in the molecule.
2. Determine the total number of valence electrons available in the atoms to be combined:
–
1
x
5e
=
5e
H
3
x
1e
=
3e
Total
=
8e
–
3. Build a skeletal structure putting the least electronegative atom in the center; hydrogens
and halogens are at the terminal ends.
4. Count shared valence electrons (2 electrons
per bond). Place remaining electrons on
most electronegative atom(s) to complete
each atom’s outer shell.
The bonds in the skeletal structure
account for 6 electrons (3 bonds). Place
the remaining 2 valance electrons on the
nitrogen to account for all 8.
5. Count electrons to be sure that the number of valence electrons used equals the number of valence electrons available.
6. If any atoms does not have a filled
outer shell, move electrons so that
they’re shared to fill outer shells using
double or triple bonds.
e.g., CO2
each O has 8 e–,
–
but C has only e 4
F:\2014-2015\330_ModChem\330_sections\330_06_Bonding\06.02a.Steps for Drawing Lewis Structures.docx (11/19/2014)
–
N
–
–
Chemistry
Lewis Structures
Draw molecular model and Lewis structures for the following molecules.
ATOM
COLOR
ATOM
COLOR
carbon
black
hydrogen
white
oxygen
red
nitrogen
blue
halogens
green
CH4 (methane)
1. atoms:
C H HH H
–
2. e dot:
–
3. v. e :
C: 1 x 4 = 4
H: 4 x 1 = 4
8
4. skeletal:
–
5. e used: 8
Lewis Structure:
skeletal structure:
H
|
H–C–H
|
H
Lewis structure = skeletal
structure
CHCl3 (chloroform)
drawing:
–
6. e unused: 0
HCl (hydrochloric acid)
H2O (water)
p. 2
Chemistry
Bonding: Lewis Structure
CH3I (iodomethane)
H2CO (formaldehyde)
C2H6 (ethane)
C2H4 (ethylene)
p.3
Chemistry
Bonding: Lewis Structure
C2H2 (acetylene)
acetic acid (CH3COOH)
OF2 (oxygen difluoride)
SiH4 (silane)
p.4