# Lab 6. Objectives  Correlate Lewis dot structures with electron domain geometries  View the effect of lone pairs of electrons on molecular shape.

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Lab 6

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. Linear 2. Trigonal planar 3. Tetrahedral 4. Trigonal bipyramidal 5. 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 “ ” 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.

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