module 3 lesson 2 VSEPR.ppt

MODULE 3
POLARITY OF
MOLECULES

MELCS:
• Determine if a molecule is polar or
nonpolar given its structure.
(S11/12PS-IIIc-15)

OBJECTIVES
At the end of the lesson, the students should be able to:
1.Explain VSEPR (Valence Shell Electron Pair Repulsion)
theory.
2.Draw the geometry of molecules using the VSEPR theory in
the Lewis dot structure.
3.Distinguish between polar and non-polar molecules.

TOPIC: Polarity of Molecules
Lesson 2: Molecular Geometry:
VSEPR (Valence Shell Electron Pair
Repulsion)

Electronegativity refers to the extent of
attraction of an atom for a shared pair of
electrons.

Types of Covalent Bond
Polar Covalent Bond
Non polar Covalent Bond

Types of covalent bonds
–Non-polar covalent: equal sharing of
electrons
–Polar covalent: unequal sharing of
electrons

EXAMPLE: HF (hydrofluoric acid)
H= 2.1 Computation: 4.0 - 2.1 = 1.9
F= 4.0 Bond: Polar Covalent

Let’s have a warm up exercise!!!

ACTIVITY 1: What Shape is this?
Directions:
Identify the geometrical shapes on the
following slides.

Molecular geometry
- pertains to the three-dimensional
arrangement of atoms in a
molecule

The approach in predicting
molecular GEOMETRY is
through………..????

VSEPR theory
Valence Shell Electron Pair
Repulsion theory

4 Key ideas of the VSEPR
theory

1st….
Electron pairs stay as far apart
from each other as possible to
minimize repulsions.

2nd….
Molecular shape is determined
by the number of bond pairs
and lone pairs around the
central atom.

Lone pair
pair of valence electrons that are not shared
with another atom in a covalent bond and is
sometimes called an unshared pair or non-
bonding pair.
found in the outermost electron shell of
atoms.
 can be identified by using a Lewis structure.

Bond pair
A bond pair is a pair of electrons
that are in a bond.
A single bond is always composed of
two electrons that are paired with
each other.
These two electrons together are
called the bond pair.

3rd…
Treat multiple bonds as if they
were single bonds (in making
the prediction).

4th…
Lone pairs occupy more volume than
bond pairs.
Lone pair – lone pair repulsions are
greater than
lone pair – bond pair repulsions
which in turn are greater than
bond pair – bond pair repulsions.

To minimize repulsion, electron
pairs ( bond pair and lone pair)
should be oriented accordingly.

Guidelines for Applying the VSEPR
Model
Step 1: Draw the Lewis structure
Step 2: Count the number of electron pairs
around the central atom.
Step 3: Use Table 2 to predict the geometry of
molecule.
Step 4: Determine the molecular geometry.
Step 5: Draw the molecular geometry.

Example: H2O
Step 1: Draw the Lewis structure

4 electron pairs around the central atom:
2 bond pairs
2 lone pairs
Step 2:Count the number of electron pairs
around the central atom

Step 3. Use the table to predict
geometry
• The arrangement of electron pairs are
tetrahedral

Step 4: Determine the molecular
geometry
Bent

Step 5: Draw/ assemble the
molecular geometry using the ball
and stick model

Let’s do this…….
Activity 2:
Given the task cards, determine the
molecular geometry of molecules by
using the ball and stick model.

Let’s do this…….
1. Draw the Lewis dot structure and
follow the VSEPR in determining the
molecular geometry of molecules.
2. Determine if the molecule is polar
or nonpolar given its structure.

Present your molecular model to the
class.

HCl
Number of electron pairs of the central atom:
4 (1 bond pair and 3 lone pairs)
Arrangement of electron pairs: tetrahedral
Molecular Geometry (VSEPR shape): linear
Geometric Sketch :

NH3
4 (1 lone pair and 3 bond pairs)
Molecular Geometry (VSEPR shape): trigonal
pyramidal
Geometric Sketch :

SO2
3 (1 lone pair and 2 bond pairs)
Arrangement of electron pairs: trigonal planar
Molecular Geometry (VSEPR shape): bent
Geometric Sketch :

BF3
3 (no lone pair)
Arrangement of electron pairs: trigonal planar
Molecular Geometry (VSEPR shape): trigonal
planar
Geometric Sketch :

CF2Cl2 (Dichlorodiflouromethane)

CF2Cl2
4 (no lone pair)
Molecular Geometry (VSEPR shape): tetrahedral
Geometric Sketch :

CH4
4(no lone pair)
Molecular Geometry (VSEPR shape): tetrahedral
Geometric Sketch :

Keep this in mind……..
VSEPR model generates realible
predictions of the geometries of
molecular structures.
Chemists use the VSEPR approach
because of its simplicity.

Keep this in mind……..
Aside from electronegativity as
factor to determine the polarity of
molecule, molecular geometry
applying the VSEPR theory is one
good way to determine whether a
molecule I polar or nonpolar.

Activity 3
• Given the Lewis structure of molecules,
predict the VSEPR Shape that
corresponds to the structure of
molecule.
• Determine if the molecule is polar or
nonpolar.

1. Beryllium Dichloride (BeCl2)

3. Carbon tetrachloride (CCl4)

6. Tellurium hexafluoride (TeF6)

7. Phosphorus pentachloride (PCl5)

1. Beryllium Dichloride (BeCl2)
Polarity polar
Molecular
Geometry
Linear

2. WATER (H2O)
Polarity POLAR
Molecular
Geometry
Bent

3. Carbon tetrachloride (CCl4)
Polarity nonpolar
Molecular
Geometry
tetrahedral

4.Sulfur trioxide (SO3)
Polarity nonpolar
Molecular
Geometry
trigonal planar

5. Sulfur trioxide ion SO3
2-
Polarity polar
Molecular Geometry trigonal pyramidal

6. Tellurium hexafluoride (TeF6)
Polarity nonpolar
Molecular
Geometry
octahedral

7. Phosphorus pentachloride (PCl5)
Polarity nonpolar
Molecular Geometry trigonal bipyramidal

Nonpolar molecule
If the shape is symmetrical due to the equal
sharing of electrons hence no dipole moment
produced.
The valence electrons are shared equally on
both sides of the atom.

Nonpolar molecule if:
the central atom does not have lone pairs
thus electrons were equally shared to
another atom of the same element
Examples: CF4 and CO2

Polar molecule
If the shape is asymmetrical due to the
unequal sharing of electrons creating a
dipole moment.
Examples: HCl, HF

Polar molecule if:
The central atom or one of the central
atoms has lone pair
Examples: H2O and NCl3

Polar molecule if:
- the central atom does not have lone pair
but bonded to atoms of different kind
Examples: CH2F2 (difloroumethane) and OCS (carbonyl
sulfide)

Summary
1. Polarity of molecules can be determined by
two ways: solving for electronegativity (from
previous lesson) and determining molecular
geometry using the VSEPR theory.
2. In determining molecular geometry using the
VSEPR theory it is a must to illustrate the
atoms Lewis dot structure.
3. Chemists use the VSEPR approach to
determine a molecules polarity due to its
simplicity.

Evaluation:
Choose the letter that corresponds to the best
answer.
1. Which of the following molecule will exhibit
tetrahedral geometry?
a. CCl4
b. CO3
c. O3
d. PCl5

2. The geometry of the molecule BF3 is?
a. linear
b. tetrahedral
c. pyramidal
d. trigonal planar

3. If there are 3 electron pairs around the
central atom of a molecule, these electron
pairs are in a ______?
a. linear
b. trigonal planar
c. trigonal pyramidal
d. bent

4. Predict the geometry and polarity of the
CS2 molecule.
a. linear, nonpolar
b. tetrahedral, polar
c. linear, polar
d. bent, polar

5. Which of the following compound
correctly matches with its molecular
geometry?
a. CO2: tetrahedral
b. NH3: trigonal pyramidal
c. H2O: linear
d. O2: bent

Assignment
Activity 5: POLARITY OF MOLECULES
Direction: Complete the table with necessary
information learned from Lesson 1 to Lesson 3.
Use the worksheet provided for your answers.

Non-polar covalent
• Sharing of electrons equally
• Usually occurs when two identical atoms
are bonded together.
• Examples: H2, O2, N2, Cl2, Br2, I2, F2

Polar covalent
• Unequal sharing of electrons
• Unequal sharing caused by 2 elements
with different electronegativities
(different abilities to attract electrons).
• The bond is called a dipole (two poles)
• Creates molecule with partial charges

• Partial charges symbolized by (delta)
+ and -
• The more electronegative atom is located
at the partially negative end
• Example: + -
H-Cl and H-Cl

Polar molecule or not?
• The shape of a molecule usually tells if a
molecule is polar or not
• If the VSEPR shape is symmetric it is
usually non-polar
• If the molecule is asymmetric it is polar

Name Polar
example
Non-polar
example
Linear HCl CO2
Trigonal Planar CH2O AlH3
Tetrahedral CH3OH CH4
Trigonal pyramidal always
Bent always
Youtube polar vs nonpolar

module 3 lesson 2 VSEPR.ppt

More Related Content

What's hot

Similar to module 3 lesson 2 VSEPR.ppt

Recently uploaded

module 3 lesson 2 VSEPR.ppt