Topic: Molecular Shape
Do Now: Draw the Lewis Dot Diagram for
N2
and
C2H2
BONDING Capacity
ELEMENT
# of bonds it likes to make
Halogen,F, Cl, Br, I
1
Hydrogen
1
O and S
2
N and P
3
C
4
Molecular Shape
H O H
Use the Lewis Structure
• Lewis structure is 2-D, but can
help figure out 3-D shape
Molecular Shape
• Shape determined by two factors:
1. # of unpaired e- around the central
atom
2. total # atoms bonded to central
atom
It’s important to classify electron pairs
as bonding or nonbonding
• Electron pairs repel each other:
• want to be as far apart from each other
as can be
• Nonbonding pairs take up a little more room
than bonding pairs
2-Atom Molecules
• Atoms located
right next to each
other
• linear molecules!
3-Atom Molecules
• linear or bent
Bent
Linear
H2 O
..
Lewis Structure of H2O = H:O:H
..
3 total atoms, free unpaired
electrons = BENT
CO2
..
..
Lewis structure: O :: C :: O
..
..
3 total atoms, no free unpaired
electrons = Linear
4 atom molecules
They make triangles…
…so we call them trigonal
Planar or pyramidal
Trigonal Pyramidal = Free electrons
around the central atom
4-Atom Molecules:
Trigonal Planar = no free electrons around
the central atom
4-Atom Molecules:
Planar
5-Atom Molecules:
H
..
H:C
:
H
..
H
Tetrahedral
Molecular Polarity
Look at structure and shape of
molecule - all bent molecules are
polar
Draw a
• If top/bottom and left/right are same
then NONPOLAR
• If either of the two are different then
POLAR
Symmetrical
Molecules
 Nonpolar – they don’t have poles
Asymmetrical
Molecules
 Polar – they have poles
(different ends)
Let’s try a few…
Name the SHAPE and
POLARITY
BENT
POLAR
Trigonal Planar
POLAR
Tetrahedral
POLAR
Trigonal Pyramidal
POLAR
linear
POLAR
linear
POLAR
bent
POLAR
tetrahedral
NONPOLAR