Chapter 6 – Covalent Compounds Section 3 – Molecular Shapes.

Chapter 6 – Covalent CompoundsSection 3 – Molecular Shapes

Chapter 6 – Covalent CompoundsSection 3 – Molecular Shapes

Determining Molecular ShapesLewis structures are two-dimensional and do not show the three dimensional shape of a molecule. However, the three-dimensional shapeof a molecule is important in determining the molecule’s physical andchemical properties.

Chapter 6 – Covalent CompoundsSection 3 – Molecular Shapes

A Lewis Structure Can Help Predict Molecular Shape

There is a model based on the valence shell electron pair repulsion (VSEPR) theory Using this model, you can predict the shape of a molecule by examining the Lewis structure of the molecule.

Unshared electrons are called lone pair electrons and influence the shape of a molecule. Lone pair electrons will push bonded pair electrons awayfrom themselves.

Chapter 6 – Covalent CompoundsSection 3 – Molecular Shapes

Shared Pairs

Lone Pair Shape of Molecule

Formula Example

Linear AB2,A2,AB CO2

F2

HBr

Bent AB2 H2O

Triginal Planer

AB3

BCl3

Triginal Pyramidal

AB3

NH3

Tetrahedral AB4

2 2

3 0

3 1

4 0

Only two atoms bondedOr double bonds to side

atoms as in CO2

CCl4

Chapter 6 – Covalent CompoundsSection 3 – Molecular Shapes

Name Shape of Molecule Name Shape of Molecule

HBr NH3

CF4 BI3

SiO2 CCl4

BF3 H2O

CO2 N2

H2S PCl3

SCl2 AsI3

BBr3 H2Te

Linear

Linear

Tetrahedral

Linear Tetrahedral

Bent

Bent

Bent

Triginal Planer

Bent

Triginal Planer

Triginal Planer

Linear

TriginalPyramidal

Triginal Pyramidal

Triginal Pyramidal

Chapter 6 – Covalent CompoundsSection 3 – Molecular Shapes

Molecular Shape Affects a Substance’s Properties

The polarity of a molecule that has more than two atoms depends on thepolarity of each bond and the way the bonds are arranged in space. If the bonds create a molecule that is symmetrical the partial polar charges ()will cancel each other out.

This will create a molecule that has polar covalent bonds but the molecule overall will be nonpolar.

Chapter 6 – Covalent CompoundsSection 3 – Molecular Shapes

O=C=OOxygen has a higher electronegativity than carbon and therefore should have a negative and carbon a positive .

- -+

However because CO2 is symmetrical the will cancel each other out and makethe molecule nonpolar. (without poles)

Chapter 6 – Covalent CompoundsSection 3 – Molecular Shapes

OH H

Place the partial polar charges on H2O. Look up electronegativity.

+

-

+

Look to see if H2O symmetrical.

H2O is not symmetrical, therefore has polar bonds and the molecule remainspolar.

Chapter 6 – Covalent CompoundsSection 3 – Molecular Shapes

The stronger the poles of a molecule the higher the melting and boiling point of the molecule.

To determine the strength of the pole find the electronegativity difference.

Which of the following solids has the highest melting point?1. H2O(s) 2. Na2O(s) 3. SO2(s) 4. CO2(s)

Chapter 6 – Covalent CompoundsSection 3 – Molecular Shapes

The electrons in a bond between two iodine atoms (I2) are shared1. equally, and the resulting bond is polar 2. equally, and the resulting bond is nonpolar 3. unequally, and the resulting bond is polar 4. unequally, and the resulting bond is nonpolar

Which electron-dot formula represents a polar molecule?

Chapter 6 – Covalent CompoundsSection 3 – Molecular Shapes

Which structural formula represents a nonpolar molecule?

Which structural formula represents a dipole?

Chapter 6 – Covalent CompoundsSection 3 – Molecular Shapes

Which type of molecule is CF4?1. polar, with a symmetrical distribution of charge 2. polar, with an asymmetrical distribution of charge 3. nonpolar, with a symmetrical distribution of charge 4. nonpolar, with an asymmetrical distribution of charge

Which formula represents a nonpolar molecule?1. CH4

2. HCl 3. H2O 4. NH3