chapter 16 alkanes and alkenes. organic chemistry chemistry of carbon compounds organic compounds...

Chapter 16

Chapter 16Alkanes and

AlkenesAlkanes and

Alkenes

ORGANIC CHEMISTRY

• Chemistry of CARBON compounds

• Organic compounds contain numerous carbon atoms

• Over 2 millions organic compounds need classifications

• Classified into families called “HOMOLOGOUS SERIES”

• 3 Homologous Series :

Alkanes

Alkenes

Alcohols

• PHYSICAL properties changes gradually down each series . As the number of carbon atoms in a molecule increases, boiling point increases, compound becomes less flammable and more viscous

HOMOLOGOUS SERIES

• A family of organic compounds with similar CHEMICAL properties• Chemical properties due to same FUNCTIONAL GROUP

AlkaneFunctional Group :

C – CCarbon-carbon Single Bond

H H H | | |H- C – C – C -H | | | H H H

FUNCTIONAL GROUPS

FUNCTIONAL GROUPS

Alkene

Functional Group :

C = CCarbon-carbon Double Bond

H H H

H- C - C = C – H

H

Alcohol

Functional Group :

-O – HHydroxy Group

H H | | H- C – C – O -H | | H H

FUNCTIONAL GROUP

NAMING OF ORGANIC COMPOUNDS

Naming is divided into 2 parts :

1st part tell the no. of carbon

1st part of name No. of carbon atoms

Meth-

Eth-

Prop-

But-

Pent-

Hex-

Hep-

Oct-

1

2

3

4

5

6

7

8

NAMING OF ORGANIC COMPOUNDS

2nd part shows the homologous series of compound

Name ending Homologous Series

-ane

-ene

-ol

Alkane

Alkene

Alcohol

Deduce the structure of

PROPANE

3 carbon atoms alkane

H H H | | |H- C – C – C -H | | | H H H

Alcohol = -ol

H H H H H | | | | |H- C – C – C – C – C – O -H | | | | H H H H H

5 carbon atoms = PENT

What is the chemical name of

PENTANOLWhat is the molecular formula ?

PHYSICAL PROPERTIES

1) Boiling Points

2) Solubility

BOILING POINTS

ALKANESNo. of carbon

Chemical Name

Molecular Formula

Rel. Molecular

Mass

Structural Formula Boiling Point

1 Methane CH4 16 H

|

H- C –H

|

H

-162

2 Ethane C2H6 30 H H

| |

H- C – C –H

| |

H H

-89

3 Propane C3H8 44 H H H

| | |

H- C – C – C –H

| | |

H H H

-42

4 Butane C4H10 58 H H H H

| | | |

H- C – C – C – C –H

| | | |

H H H H

-0.5

BOILING CURVE OF ALKANESB

oilin

g P

oin

t o C

200

150

100

50

0

-50

-100

-150

-200

No. of Carbon2 4 6 8 10

Methane

Ethane

Propane

ButanePentane

Hexane

The boiling point increases down a homologous series

BOILING POINTS

Alkanes are covalent compounds. They have low boiling point

Alkanes are gases or liquids at room temperature.

Why does boiling point increases down a homologous series?

BOILING POINTS

As carbon number increases, molecular size also increases.

The larger the size of molecules, the greater is the van der Waals forces

between them

SOLUBILITY

THREE

SOLUBILITY OF ALKANES

From these products, what can you say about the solubility of alkanes?

Refer to Handout “Chief Uses of Oil Products”

They are not soluble because they are oil-based

SOLUBILITY OF ALKANES

All alkanes are NOT soluble

alkanesalkanes

a group of organic compounds with the general formula, CnH2n+2, where n is the number of carbon atoms in one molecule

names of alkanes end in –ane

are molecular compounds

have low boiling points; tend to be liquids and gases at room conditions

are insoluble in water

a group of organic compounds with the general formula, CnH2n+2, where n is the number of carbon atoms in one molecule

names of alkanes end in –ane

are molecular compounds

have low boiling points; tend to be liquids and gases at room conditions

are insoluble in water

alkanesalkanes

a ball-and-stick model of methane,

CH4

alkanesalkanes

alkanes burn in air to form CO2 and H2O

example: combustion of propane, C3H8

alkanes burn in air to form CO2 and H2O

example: combustion of propane, C3H8

combustioncombustion

C3H8 + 5O2 3CO2 + 4H2O

incomplete combustion results in the formation of carbon monoxide, CO and soot, C

incomplete combustion results in the formation of carbon monoxide, CO and soot, C

alkanesalkanes

main use of alkanes is in combustion to produce energy:

main use of alkanes is in combustion to produce energy:

o bottled gas for cookingo fuels for buses and carso fuels for aircrafts

o bottled gas for cookingo fuels for buses and carso fuels for aircrafts

uses of alkanesuses of alkanes

alkanesalkanes

alkanes react with chlorine in the presence of light

example: substitution reaction of methane with chlorine

alkanes react with chlorine in the presence of light

example: substitution reaction of methane with chlorine

substitution with chlorinesubstitution with chlorine

CH4 + Cl2 CH3Cl + HCl

o a hydrogen atom in methane is replaced by a chlorine atom

o This is called a substitution reaction

o more hydrogen atoms in methane can be replaced by chlorine atoms to produce organic halogen compounds (CH2Cl2, CHCl3 and CCl4)

o a hydrogen atom in methane is replaced by a chlorine atom

o This is called a substitution reaction

o more hydrogen atoms in methane can be replaced by chlorine atoms to produce organic halogen compounds (CH2Cl2, CHCl3 and CCl4)

Story of a Star

Starry

Candies!!!

Starry

Substitution

Substitution

Starry

Time for Chemistry!

Starry

Carbon atom

Hydrogen atom

Chlorine atom

Covalent bonds

Time for Chemistry!

Starry C

H

H

H

H

Cl Cl

Time for Chemistry!

C

H

H

Cl

HStarry

H Cl

Substitution Reaction

• A reaction in which one or more atoms of an organic compound are replaced with one or more other atoms

C

H

H

H

H C

H

H

Cl

H

• Methane + Chlorine Monochloromethane + Hydrogen Chloride

+ Cl-Cl + HCl

CH4 + Cl2 CH3Cl + HCl

monochloromethane

Substitution Reaction

• Write out the substitution equations if monochloromethane is further substituted with more chlorine molecules. What will the final product be?

CH4(g) + Cl2(g) CH3Cl (g) + HCl (g)

monochloromethane

Substitution Reaction

When more chlorine is added,

+ +C

H

H

Cl

H C

H

Cl

Cl

HCl-Cl HCl

CH3Cl (g) + Cl2(g) CH2Cl2(g) + HCl (g)

dichloromethanemonochloromethane

Substitution Reaction

When more chlorine is added,

C

H

Cl

Cl

H C

Cl

Cl

Cl

H+ Cl-Cl + HCl

CH2Cl2(g) + Cl2(g) CHCl3(l) + HCl(g)

trichloromethane

For your information :

Trichloromethane is commonly called chloroform and is very useful as an anaesthetic

dichloromethane

Substitution Reaction

When more chlorine is added,

C

Cl

Cl

Cl

H C

Cl

Cl

Cl

Cl+ Cl-Cl + HCl

CHCl3 + Cl2 CCl4 + HCl

tetrachloromethane

For your information :

Tetrachloromethane is a valuable solvent, used in dry cleaning because it is very volatile and good at dissolving grease and dirt.

trichloromethane

Summary

• Alkanes

- CombustionAlkanes + Oxygen

Carbon dioxide + water

- Substitution- with Chlorine to form

variety of substituted products

End of alkanes

Coming soon : test on fuels and alkanes