Lewis Structure Guidelines
1. Determine the total number of valence electrons
2. The central atom is the least electronegative atom with the exception of hydrogen
3. Draw structure symmetrically with single bonds
4. Subtract the bonding electrons from the total valence electrons – put 6e- on the outer atoms
(except H) and the remainder on the central
5. If the central atom has less than 8e- add a bond for every 2e- that’s missing – exceptions Be, B
or Al – these elements can have less than an octet
Formal Charge ⇒ Group Number - # bonds - # non-bonded electrons
Resonance structures ⇒ More than one valid Lewis structure where each structure contributes to a
hybrid or true structure – structure with minimum formal charge is the most stable and will contribute
to the hybrid the most – a (-) formal charge is more stable if on the most EN atom whereas a (+) formal
charge is more stable on the least EN atom
Electronic
Domains
Generic
Formula
Electronic and
molecular
geometry
2
AX2E0
3
3
4
4
4
5
Bond
Angle
Hybridization
of central atom
EG/MG ⇒
Linear
180°
sp
AX3E0
EG/MG ⇒
Trigonal planar
120°
sp2
AX2E1
EG ⇒ Trigonal
planar
MG ⇒ Bent or
V-shaped
<120°
sp2
109.5°
sp3
<109.5°
sp3
<109.5°
sp3
90°/120°
dsp3
AX4E0
AX3E1
AX2E2
AX5E0
Picture
** => always polar
**
EG/MG ⇒
Tetrahedral
EG ⇒
Tetrahedral
MG ⇒ Trigonal
Pyramid
EG ⇒
Tetrahedral
MG ⇒ Bent or
V-shaped
EG/MG ⇒
Trigonal
bipyramid
**
**
Electronic
Domians
Generic
Formula
Electronic and
molecular
geometry
5
AX4E1
EG ⇒ Trigonal
bipyramid
MG => See-Saw
5
5
AX3E2
AX2E3
Picture
** => always polar
Bond
Angle
Hybridization
of central atom
<90°/<120°
dsp3
<90°
dsp3
180°
dsp3
90°
d2sp3
<90°
d2sp3
90°
d2sp3
<90°
d2sp3
180°
d2sp3
**
EG ⇒ Trigonal
bipyramid
MG ⇒ T-shaped
**
EG ⇒ Trigonal
bipyramid
MG ⇒ linear
6
6
AX6E0
AX5E1
6
AX4E2
6
AX3E3
6
AX2E4
EG/MG ⇒
Octahedral
EG ⇒
Octahedral
MG ⇒ Square
pyramid
EG ⇒
Octahedral
MG ⇒ Square
planar
EG ⇒
Octahedral
MG ⇒ T-shaped
EG ⇒
Octahedral
MG ⇒ linear
**
**
Molecular Polarity ⇒ Molecules are polar or have a non-zero dipole moment if there’s an uneven
distribution of bonding electrons. Non-polar molecules have no dipole moment due to an even or
symmetrical distribution of bonding electrons
1.
Are all of the central atoms the same (if more than one) and all of the outer atoms the same?
a. no ⇒ it’s polar (has a non-zero dipole moment)
b. yes ⇒ keep going
2. Does the central atom have lone pairs?
a. no ⇒ non-polar
b. yes ⇒ keep going
3. Is the molecular geometry linear or square planar?
a. no ⇒ polar
b. yes ⇒ non-polar