Lewis Structures. 1. Start by determining the formula and the total number of valence electrons. 2. The central atom is the 1 st element in the formula.  It will never be hydrogen. Carbon is always the central atom. 3. Connect the central atom to the outer atoms with a single bond.
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1. Start by determining the formula and the total number of valence electrons.
2. The central atom is the 1st element in the formula.
 It will never be hydrogen. Carbon is always the central atom.
3. Connect the central atom to the outer atoms with a single bond.
4. Determine the number of remaining electrons.
5. Place the remaining electrons around the outer atoms so each obeys the octet rule.
6. Any remaining electrons go on the central atom.
7. Check to make sure each atom obeys the octet rule.
 If the central atom does not, take a pair from an outer atom and make a double bond with the central atom.

 

Li
H
He
VSEPR Theory
180o
2
2
0
linear
CO2
line
120o
3
3
0
trigonal
planar
BF3
triangle
••
120o
trigonal
planar
bent
3
2
1
SO2
boomerang
total #
e groups
#
bond
#
lone pairs
molecular
geometry
structure
e.g.
CH4
pyramid
4
4
0
tetrahedral
total #
e groups
#
bond
#
lone pairs
molecular
geometry
structure
e.g.
e groups
#
bond
#
lone pairs
molecular
geometry
structure
e.g.
109.5o
CH4
pyramid
4
4
0
tetrahedral
••
<109.5o
4
3
1
tetrahedral
trigonal
pyramidal
NH3
tripod
••
<109.5o
tetrahedral
bent
4
2
2
H2O
“v”
••