Lab 6
MOLECULAR GEOMETRY
Objectives
 Correlate Lewis dot structures with electron
domain geometries
 View the effect of lone pairs of electrons on
molecular shape
Materials
 5 molecular models representing the 5 basic
electron domain geometries
 13 balloon models representing the 13 different
molecular geometries
How to determine the 3D
structure of a molecule
 Step 1: Draw the Lewis structure
 Step 2: Determine electron-domain geometry
around the central atom.
 Step 3: Determine the molecular geometry
Step 2:
Determine electron
domain geometry
 VSEPR theory – a model used to predict the 3D
structure of individual molecules. This theory is
based on the idea that electrons repel each
other.
 Electron domain geometry describes the
geometric arrangement of electrons around an
atom (bonds and/or lone pair(s) of electrons).
Step 2:
Determine electron
domain geometry
 There are 5 basic electron domain geometries
1.
2.
3.
4.
5.
Linear
Trigonal planar
Tetrahedral
Trigonal bipyramidal
Octahedral
Step 3:
Determine the
molecular geometry
 Linear
 Trigonal Planar (Bent)
 Tetrahedral (trigonal pyramid; bent)
 Trigonal bipyramidal (Seesaw; T shaped)
 Octahedral (Square pyramid; square planar)
 (Show some examples and diagrams)
Lab 6: Procedure/Data
Collection
 Station 1 – Lewis Structures and Molecular
Models
- 1 set of eight substances (Table 2 pg
64) are assigned (workshop handout).
- In the lab, match the Lewis structure
to one of the 5 molecular models on the
lab bench.
-(Table 3 pg 65) Identify the correct model
number (and molecular formula), name
the electron-domain geometry, draw the
3D structure, and label all ideal bond
angles.
Lab 6: Procedure/Data
Collection
 Station 2 – VSEPR and Balloon Models: effect of
lone pairs on molecular shape.
- Again, you are to match the Lewis
structure (from workshop) to one of the
balloon models representing
VSEPR structures.
-Balloons represent the space occupied
by either bonding pairs or lone pairs.
Station 4 – cont.
 (Table 4 pg 67 & 68)
 Identify the VSEPR model number
 Name the molecular geometry (shape) (e.g.
Bent, Seesaw, T shaped etc.)
 Draw the 3D structure
 Label all bond angles in your structure, indicating
distortions using “<“ or “>” signs.
At the end of the lab…
 Turn in today’s lab write-up and all of the
workshop handouts.
 Lab 9 write-up, naming compounds H.W. and lab
6 (handout from last week) are due in the
beginning of the lab.