Transcript Molecular VSEPR Models

MOLECULAR
STRUCTURES
CH4
GUMDROP MOLECULE ACTIVITY
Draw the Lewis dot structure for the molecule
Use gumdrops, marshmallows, and toothpicks to
build a 3D representation of the molecule
 Gumdrop=atom
 Toothpick=bond
 Small marshmallow=shared electron pair
 Large marshmallow=lone electron pair
 Draw a sketch on sheet of your molecule (remember a
key!)
LETS LOOK AT METHANE (CH4)…
What do you notice about methane?
How many shared electron pairs are
surrounding the central carbon?
 Enter number into Quizdom Remote
LETS LOOK AT METHANE (CH4)…
What do you notice about methane?
Can it bond with anything else?
Yes
No
LETS LOOK AT METHANE (CH4)…
3D Model: Jmol perspective
Bond Angle: 109.5°
Molecular Shape Name:
Tetrahedral
4 pairs. All Shared.
NH3
GUMDROP MOLECULE ACTIVITY
Draw the Lewis dot structure for the molecule
Use gumdrops, marshmallows, and toothpicks to
build a 3D representation of the molecule
 Gumdrop=atom
 Toothpick=bond
 Small marshmallow=shared electron pair
 Large marshmallow=lone electron pair
 Draw a sketch on sheet of your molecule (remember a
key!)
NOW, HOW ABOUT AMMONIA (NH3)?
How many shared pairs of electrons are there?
NOW, HOW ABOUT AMMONIA (NH3)?
How many shared pairs of electrons are there?
Predict what you think will happen to the bond
angles between the hydrogens in ammonia
compared to the hydrogens in methane:
 A) The angle will increase
 B) The angle will decrease
 C) The angle will remain the same
LETS LOOK AT AMMONIA (NH3)…
3D Model: Jmol perspective
With lone pairs
Bond Angle: 107.6°
Molecular Shape Name:
Trigonal pyramidal
4 pairs: 3 shared. 1 lone pair
WHAT WOULD HAPPEN IF THERE WAS NO
LONE PAIR ON AMMONIA?
BH3
FOR BH3 …
How many unshared pairs of electrons exist
around the central atom?
WHAT DOES BH3 LOOK LIKE?
3D Model: Jmol perspective
Bond Angle: 120°
Molecular Shape Name:
Trigonal planar
3 pairs: 3 shared. 0 lone pair
H2O
NOW LET’S TAKE ANOTHER ELECTRON PAIR OFF…
WHAT WILL H2O LOOK LIKE?
Which is NOT true about the relationship
between water and ammonia?
 A) The bond angle is greater for water than it is for
ammonia
 B) The bond angle is smaller for water than it is for
ammonia
 C) There are more lone pairs in water
 D) There are fewer shared pairs in water
H2O…IT’S EVERYWHERE
3D Model: Jmol perspective
With Lone Pairs
Bond Angle: 104.5°
Molecular Shape Name:
Bent
4 pairs: 2 shared. 2 lone pair
CO2
WHAT IS DIFFERENT FOR CO2?
How many lone pairs are there?
WHAT IS DIFFERENT FOR CO2?
How many lone pairs are there?
How many covalent bonds are formed around the
carbon?
LET’S LOOK AT CO2…
3D Model: Jmol perspective
Bond Angle: 180°
Molecular Shape Name:
Linear
4 pairs: 4 shared. 0 lone pair
EASY ENOUGH…LETS SEE IF WE CAN
USE OUR CHART TO PREDICT FOR
OTHER MOLECULES
WHAT DO YOU THINK ABOUT BeCl2?
How many shared pairs are there?
WHAT DO YOU THINK ABOUT BeCl2?
How many shared pairs are there?
How many lone pairs are there around the central
atom?
NOW LET’S LOOK AT H2S
How many lone pairs are there?
NOW LET’S LOOK AT H2S
How many lone pairs are there?
What would the bond angle be?
FOR PH3…
How many lone pairs are there?
FOR PH3…
How many lone pairs are there?
The bond angle for PH3 is ______ compared to
CH4.
 A) Larger
 B) Smaller
 C) The same
HOW ABOUT CCl4?
How many shared pairs around central atom?
HOW ABOUT CCl4?
How many shared pairs around central atom?
How many lone pairs?
HOW ABOUT CCl4?
How many shared pairs around central atom?
How many lone pairs?
What would you predict the bond angle would be?
PCl5
EXPANDED OCTET: PCl5
Trigonal Bipyramidal
 Jmol representation
 Bond Angles: 90° and 120°
 5 Total Pairs: 5 Shared pairs 0 Lone Pairs
EXPANED OCTET… CONT.
Octahedral : SF6
 Jmol Representation
 Bond Angles: 90°
 6 Total Pairs: 6 shared, 0 Lone Pairs
OCTAHEDRAL : SF6
What do you think would happen if you removed an Fluorine
from the central Sulfur atom?
What if you removed another?
How do you think this would affect the molecular model?
VALENCE SHELL ELECTRON PAIR
REPULSION THEORY
The molecular structure is based on electrons (Shared or
unshared) arranging themselves so that they have the greatest
distance between one another around the central atom.
The goal is to minimize the repulsion between the negativelycharged electrons.