SHAPES OF MOLECULESSHAPES OF MOLECULES

COVALENT BONDCOVALENT BOND

ByBy

RIMKHONG GROUPRIMKHONG GROUP

LOOK AT THIS VDOLOOK AT THIS VDO

Before you start it would be helpful to…

• know the definition of a covalent bond

• know what a lone pair is

• know that like charges repel

SHAPES OF MOLECULESSHAPES OF MOLECULES

is the chemical bond that involves the sharing of pairs of electrons between atoms.

Covalent BondCovalent Bond

ELECTRON PAIR REPULSION THEORYELECTRON PAIR REPULSION THEORY

“THE SHAPE ADOPTED BY A SIMPLE MOLECULE OR ION IS THAT WHICH KEEPS REPULSIVE FORCES TO A MINIMUM”

AlBonds are further apart so repulsive forces are less

Bonds are closer together so repulsive forces are greater

Al

All bonds are equally spaced out as far apart as possible

REGULAR SHAPESREGULAR SHAPES

Molecules, or ions, possessing ONLY BOND PAIRS of electrons fit into a set of standard shapes.

All the bond pair-bond pair repulsions are equal.

All you need to do is to count up the number of bond pairs and chose one of the following

C

A covalent bond will repel another covalent bond

examples...

REGULAR SHAPESREGULAR SHAPES

2 LINEAR 180º BeCl2

3 TRIGONAL PLANAR 120º AlCl3

4 TETRAHEDRAL 109.5º CH4

5 TRIGONAL BIPYRAMIDAL 90º & 120º PCl5

6 OCTAHEDRAL 90º SF6

BOND BONDPAIRS SHAPE ANGLE(S) EXAMPLE

BERYLLIUM CHLORIDEBERYLLIUM CHLORIDE

Cl ClBe180°

BOND PAIRS 2

LONE PAIRS 0

BOND ANGLE...

SHAPE...

180°

LINEAR

ClBe Be ClCl

LINEARLINEAR

Al

ALUMINIUM CHLORIDEALUMINIUM CHLORIDE

Cl

Cl

Al120°

Cl

ClAl

Cl

Cl

Cl

BOND PAIRS 3

LONE PAIRS 0

BOND ANGLE...

SHAPE...

120°

TRIGONAL PLANAR

TRIGONAL PLANAR

METHANEMETHANE

BOND PAIRS 4

LONE PAIRS 0

BOND ANGLE...

SHAPE...

109.5°

TETRAHEDRAL

C H CH

H

H

H

109.5°

H H

C

H

H

TETRAHEDRAL

PHOSPHORUS(V)FLUORIDEPHOSPHORUS(V)FLUORIDE

FP

P

F

F

F

F

FBOND PAIRS 5

LONE PAIRS 0

BOND ANGLE...

SHAPE...

120° & 90°

TRIGONAL BIPYRAMIDAL

120°F

F

P

F

FF

90°

TRIGONAL

BIPYRAMIDAL

TRIGONAL

BIPYRAMIDAL

SULPHUR(VI) FLUORIDESULPHUR(VI) FLUORIDE

FS

BOND PAIRS 6

LONE PAIRS 0

BOND ANGLE...

SHAPE...

90°

OCTAHEDRAL

S

F

F

F

F

F

F

F

F F

FS

F

F

90°

OCTAHEDRAL

OCTAHEDRAL

ARE YOU OK!summaryTo predict the shape of a molecule: (1)Write down the Lewis dot structure for the molecule. (2)Count the number of bond pairs and lone pairs around the central atom. (3) Decide on the electron pair orientation based on the total number of electron pairs (4 = tetrahedral, 5 = trigonal bipyramidal). (4) Consider the placement of lone pairs and any distortions from "regular" shapes. (5) Name the shape based on the location of atoms

summary

CO2

CCl4

NCl5

HCN

BCl3

NH3

TEST QUESTIONSFor each of the following molecules state the number of bond pairs

state the shapestate the bond angle(s)

CO2

CCl4

NCl5

HCN

BCl3

NH3

Linear

BOND BONDPAIRS SHAPE ANGLE(S)

2 180º

Tetrahedral4 109.5º

Trigonal BipyramidalTrigonal Bipyramidal55 90º 120º90º 120º

Linear2 180º

Trigonal PlanarTrigonal Planar33 120º120º

Trigonal PyramidalTrigonal Pyramidal33 107º107º

TEST QUESTIONS

SHAPES OF SHAPES OF MOLECULESMOLECULES

The EndThe End