Download LEWIS DOT STRUCTURES , MOLECULAR SHAPES, AND

LEWIS DOT STRUCTURES and VSEPR MOLECULAR SHAPES
Valence electrons— electrons occupying the last s & p sublevels used. The number of valence electrons is easily
determined for Representative elements. You simply need to look at the group number. Examples: Group 1A elements
like sodium have 1 valence electron. Group 6A elements like oxygen have 6 valence electrons.
Lewis Structures—a representation of a molecule which reflects atoms present and the number of shared and unshared
electrons present.
Lone pair—non bonded electron pair
Bonding electrons—pairs of electrons shared between 2 atoms
ELECTRONIC GEOMETRY—the basic arrangement of atoms about a central atom. It is determined by counting the
total number of atoms bound to central atom and adding it to the number of lone pairs on the central atom. This total will
be equal to a value 1-6. Those numbers correspond to one of the basis shapes in bold .
MOLECULAR GEOMETRY—the specific geometry of atomic arrangement around a central atom based upon bond
atoms and lone pairs.
How to Construct Lewis Dot Structures for Molecules:
1. Determine the type and number of atoms present in the molecule
2. Determine the number of valence electrons each atom will supply (you may wish to draw the electron dot diagram for
that atom) If you are asked to do the structure of a polyatomic ion: add to the total number of electrons if the ion is
negative; subtract from the total number of electrons if the ion is positive.
Example: if an ion has a –3 charge, add 3 more electrons to the total of valence electrons.
3. Total the number of valence electrons in the atoms to be combined
4. Arrange the atoms to form a skeletal structure for the molecule. The central atom is always the least electronegative
atom. (Hydrogen is never the central atom!)
5. Add connect the atoms by adding electron pair bonds.
6. Add unshared electron pairs around the remaining atoms so that everything is satisfied with an octet (note some atoms
like hydrogen are satisfied when they have 2 valence electrons).
7. Count to make sure that the number of electrons used equals the number of electrons available.
- if too many electrons are used, take away one or more lone pairs (non-bonded electron pairs) until the correct
number of electrons is achieved. Then move 1 (or more) of the lone pairs to a bonding position between a non-hydrogen
atom and a central atom to form a double bond.
ELECTRONIC GEOMETRY AND VSEPR MOLECULAR GEOMETRY:
To determine a geometry, first construct a Lewis structure, then consult the table below:
# of atoms
bonded to
Central atom
# of Lone
pairs of
electrons
Electronic Geometry
VSEPR Molecular Geometry
Predicted
Bond
Angles
Example
Molecule
2
0
Linear
Linear
180˚
BeCl2
Hybridization
sp
3
0
Planar Triangle
Planar Triangle
120˚
BF3
sp2
2
4
1
0
Planar Triangle
Tetrahedral
Bent (angular)
Tetrahedral
109.5˚
SnCl2
CH4
sp2
sp3
3
1
Tetrahedral
Trigonal-pyramidal
107
NH3
sp3
2
2
Tetrahedral
Bent
104.9
water
sp3
1
3
Tetrahedral
linear
HF
sp3
5
0
Trigonalbypyramidal
Trigonal-bypyramidal
PCl5
sp3d
4
1
Trigonalbypyramidal
SF4
sp3d
3
2
ClF3
sp3d
2
3
Linear
XeF2
sp3d
6
0
Trigonalbypyramidal
Trigonalbypyramidal
Octahedral
See-saw
(unsymmetrical
tetrahedral)
T-shaped
SF6
sp3d2
5
1
Octahedral
Square Pyramidal
BrF5
sp3d2
4
2
Octahedral
Square Planar
XeF4
sp3d2
Octahedral
120˚,
90˚
90˚
Pre AP Chemistry Electronic and Molecular Geometry Worksheet HW 2A
To determine molecular geometry, first construct a Lewis structure, then consult the table below:
MOLECULE
1
OCl2
2
HF
3
CHCl3
4
H2S
5
CO2
6
CH3OH
7
O2
8
ICl3
Total
Number
of
Valence
Electrons
Available
Lewis Dot
Structure
Predicted
Molecular shape
Is it polar?
Hybridization
Possible
types of
I.M.F’s
MOLECULE
9
N2
10
(SO3)-2
11
KrF4
12
IF5
13
COS
14
CF2Cl2
15
*HNO3
16
SeCl6
Total
Number
of
Valence
Electrons
Available
Lewis
Structure---
Predicted
Molecular shape
Is it
polar?
Hybridization
Possible
types of
I.M.F’s