Guidelines for writing Lewis Dot Structures
• Identify the central atom (the atom to
which the other atoms will be attached)
- The central atom is the one having the lowest
ionization energy (or lowest electronegativity)
• Determine the total number of valence
electrons
– Remember to include any extra electrons, if
present
Guidelines for writing Lewis Dot Structures
• Arrange atoms in a symmetrical fashion
(remember that this is being done in 2
dimensions rather than 3)
• Use a single pair of electrons for each
bond
• Place remaining electrons around the rest
of the atoms in groups of 2
Guidelines for writing Lewis Dot Structures
• Use the OCTET RULE to determine the
exact arrangement of electrons with each
atom
• The only exception to the octet rule is
hydrogen which requires only 2 electrons.
Guidelines for writing Lewis Dot Structures
• Sharing of a single pair of electrons
between two atoms constitutes a single
bond which is called a sigma bond ()
• The electrons in a bond are counted twice,
once with each of the atoms that form the
bond to determine if the octet rule is
satisified
Guidelines for writing Lewis Dot Structures
• Sharing of two or more pairs of electrons between 2
atoms constitutes a multiple bond
-The first pair of electrons is a sigma
bond ()
- each of the remaining pairs of electrons
forms a bond which is called a pi bond ()
Resonance
Sigma and Pi Bonds
• A sigma () bond centers along the
internuclear axis.
• A pi () bond occupies the space above
and below the internuclear axis.
Summary of Bonding Types
# of 
bonds
4
3
2
# of 
Steric
bonds
Number
(Honors)
0
0
0
4
4
4
# of pairs of
non-bonded
electrons
0
1
2
3
1
3
0
2
2
2
0
VSEPR
designation
sp3
sp3
sp3
sp2
sp
Bond
angle, 
Molecular
Geometry
109.5
Tetrahedral
107.5
Trigonal Pyramidal
104.5
Bent
120
Trigonal Planar
180
Linear