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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
