Chapter 16 Alkanes 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

Alkane Functional Group : C – C Carbon-carbon Single Bond H H H | | | H- C – C – C -H | | | H H H FUNCTIONAL GROUPS

Alkene Functional Group : C = C Carbon-carbon Double Bond H H H H- C - C = C – H H

Alcohol Functional Group : -O – H Hydroxy Group H H | | H- C – C – O -H | | H H FUNCTIONAL GROUP

NAMING OF ORGANIC COMPOUNDS Naming is divided into 2 parts : 1 st part tell the no. of carbon 1 st part of nameNo. of carbon atoms Meth- Eth- Prop- But- Pent- Hex- Hep- Oct

NAMING OF ORGANIC COMPOUNDS 2nd part shows the homologous series of compound Name endingHomologous Series -ane -ene -ol Alkane Alkene Alcohol

Deduce the structure of PROPANE 3 carbon atomsalkane 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 PENTANOL What is the molecular formula ?

PHYSICAL PROPERTIES 1) Boiling Points 2) Solubility

BOILING POINTS

ALKANES No. of carbon Chemical Name Molecular Formula Rel. Molecular Mass Structural FormulaBoiling Point 1MethaneCH 4 16 H | H- C –H | H EthaneC2H6C2H6 30 H | H- C – C –H | H -89 3PropaneC3H8C3H8 44 H H H | | | H- C – C – C –H | | | H H H -42 4ButaneC 4 H H H | | H- C – C – C – C –H | | H H H H -0.5

BOILING CURVE OF ALKANES Boiling Point o C No. of Carbon Methane Ethane Propane Butane Pentane 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

alkanes  a group of organic compounds with the general formula, C n H 2n+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, C n H 2n+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 alkanes a ball-and-stick model of methane, CH 4

alkanes  alkanes burn in air to form CO 2 and H 2 O  example: combustion of propane, C 3 H 8  alkanes burn in air to form CO 2 and H 2 O  example: combustion of propane, C 3 H 8 combustion C 3 H 8 + 5O 2 3CO 2 + 4H 2 O  incomplete combustion results in the formation of carbon monoxide, CO and soot, C

alkanes  main use of alkanes is in combustion to produce energy: o bottled gas for cooking o fuels for buses and cars o fuels for aircrafts o bottled gas for cooking o fuels for buses and cars o fuels for aircrafts uses of alkanes

alkanes  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 chlorine CH 4 + C l 2 CH 3 C l + HC l 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 (CH 2 C l 2, CHC l 3 and CC l 4 ) 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 (CH 2 C l 2, CHC l 3 and CC l 4 )

Story of a Star Starry

Candies!!! Starry

Substitution Starry

Time for Chemistry! Starry Carbon atom Hydrogen atom Chlorine atom Covalent bonds

Time for Chemistry! Starry C H H H H Cl

Time for Chemistry! C H H Cl H Starry 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 CH 4 + Cl 2 CH 3 Cl + HCl monochloromethane

Substitution Reaction Write out the substitution equations if monochloromethane is further substituted with more chlorine molecules. What will the final product be? CH 4(g) + Cl 2(g) CH 3 Cl (g) + HCl (g) monochloromethane

Substitution Reaction When more chlorine is added, + + C H H Cl H C H H Cl-Cl HCl CH 3 Cl (g) + Cl 2(g) CH 2 Cl 2(g) + HCl (g) dichloromethane monochloromethane

Substitution Reaction When more chlorine is added, C H Cl H C H + Cl-Cl+ HCl CH 2 Cl 2(g) + Cl 2(g) CHCl 3(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 H C + Cl-Cl+ HCl CHCl 3 + Cl 2 CCl 4 + 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 - Combustion Alkanes + Oxygen Carbon dioxide + water - Substitution - with Chlorine to form variety of substituted products

End of alkanes Coming soon : test on fuels and alkanes