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    Alkanes power point Alkanes power point Presentation Transcript

    • Overview of Organic Chemistry
    • Organic Compounds in Daily Life
      Can you identify organic compounds from this
      picture? 
      Road surface (bitumen)
      Fuel in car
    • Some Brief History
      MrFriedrich Wöhler
      Born: 31-Jul-1800
      Birthplace:Eschersheim, Germany
      Died: 23-Sep-1882
      • He changed the belief that organic compounds could only be made by living things.
      • Organic compounds are compounds that contain the element Carbon (C).
      • Most organic compounds also contain hydrogen (H).
      • Organic compounds that contain only carbon and hydrogen are called hydrocarbons.
    • Question Time!
      Q: Do all compounds containing carbon
      considered as organic compounds?
      A: No. Chemists consider carbonates and oxides
      of carbon as INORGANIC compounds rather
      than organic.
      Examples of inorganic compounds:
    • Some Real Life Incidents In Singapore (NE ISSUES)
      Q: Why do you think Singapore imposed very harsh measure to control pollution of our air and the environment?
    • How Do We Classify Organic Compounds
      Recall… On the topic of Periodic table..
      • We classified elements into families (group I, II ,III…).which had similar properties..
      On the topic of Organic Chemistry..
      • We classify organic compounds into families known as the homologous series which have similar chemical properties within the series.
    • How Do We Classify Organic Compounds
      A homologous series is a family of organic compounds with
      Similar chemical properties
      Similar functional group (reactive group)
      Same general formula
      Organic compounds in the same homologous series have
      Similar chemical properties because they have the same functional group
      Different physical properties due to different chain length (number of carbon atoms per molecule)
      Learning Point 1: As the number of carbon atoms increases, there is
      a gradual change in the physical properties.
    • How Do We Classify Organic Compounds
      The table below shows 4 homologous series, their functional groups and
      their general formula we will learn in this topic of Organic Chemistry.
      n refers to the number of carbon atoms
    • Naming Organic Compounds
      The table below shows 4 homologous series, their functional groups and
      their general formula we will learn in this topic of Organic Chemistry.
    • Question Time 2!
      Q: Where do you use/find alkanes in everyday life?
    • Activity: Time To Use Your Creative Juices!
      • Get into groups of 5 students each.
      • Complete this task in 2 minutes.
      Your Group Task:
      As a group, come up with a mnemonic for memorizing the prefixes for the first four alkanes (methane, ethane, propane, butane).
      My Version: Mike Eats Peanut Butter
      Disclaimer: Best group will get a special present from me!
    • Interactive Activity: ChemSketch Molecular Modelling
      Time to learn more about the physical properties of alkanes!
    • ChemSketch Molecular Modelling Activity (30Mins)
      In your groups of 5, you are to:
      Complete your individual worksheet by working together
      as a group to think about the questions and answering the questions.
      The complete worksheet must be submitted at the end of the lesson.
      Follow the instructions in the worksheet.
      Raise your hand to ask for assistance if your group encounters any problems or in doubt.
      Have Fun!! 
    • Reflection: ChemSketch Molecular Modelling Activity
      You have learnt 7 important concepts:
      How to draw 2D structural formula for Alkanes (C1-C5) and Alkenes (C2-C4)
      Derived the general formula of Alkanes CnH2n+2
      Derived the general formula of Alkenes CnH2n
      Alkanes are saturated (contains single C-C)
      Alkenes are unsaturated (contains C=C)
      As the no. of carbon atoms increases, the physical properties show a gradual change (m.p., b.p., state at r.t.p.)
      Isomerism starts from butane, how to draw isomers of butane and understand the term isomerism.
    • Chemical Properties of Alkanes
    • Chemical Properties of Alkanes
      • Alkanes are unreactive as their C-C and C-H bonds are very strong and difficult to break.
      • They do not react with acids, alkalis, metals or oxidizing agents!
      **Fun Fact: Alkanes used to be called paraffins **
      • In Latin  Parum = little
       Affinities = affinity
      • Named as such in the past because alkanes undergo few reactions
    • Reactions Of Alkanes
      • All alkanes have similar chemical properties because they belong to the same homologous series.
      • Alkanes are rather unreactive; they not react with most chemicals.
      • However, they undergo 2 main types of reaction:
    • Combustion Reaction (2 Types)
      Complete Combustion
      Incomplete Combustion
    • Combustion (Complete)
      • Alkanes are called saturated hydrocarbons because they only have single bonds between carbon atoms (C-C).
      • Alkanes burn in a plentiful supply of air to release energy (this is why they are used as fuels).
      Gas supplied here refers to Alkanes !!
      Recall your Bunsen Burner..
    • Combustion (Complete)
      • Burning (properly called combustion) also produces :
      Carbon dioxide (CO2)
      Water Vapour (H2O)
      Lets observe what happens when you light a bunsen burner!
    • Combustion (Complete)
      Lets break it down frame by frame:
      Methane gas (CH4) exits from the mouth the Bunsen Burner and mixes with the oxygen gas (O2) in the atmosphere
      A flame is placed near the mouth of the Bunsen Burner.
    • Combustion (Complete)
      Lets break it down frame by frame:
      Methane gas (CH4) burnsin oxygen gas (O2) in the surrounding atmosphere (process: combustion)
      The products of the combustion are CO2 and H2O.
      Complete combustion  Blue, non-luminous flame !
    • Combustion (Complete)
      Writing A Balanced Equation : Complete Combustion of Methane
      Word Equation: Methane(g) + Oxygen(g)  Carbon dioxide(g) + Water(l) + Heat
      Note: Heat is always evolved from the combustion. In the following equations, I will omit it for clarity.
      Chemical Equation:
      Step 1: CH4(g) + O2(g)  CO2(g) + H2O(l) [Write the chemical equation]
      Step 2:CH4(g) + O2(g)  CO2(g) + 2H2O(l) [Balance the equation]
      How to Balance Combustion Reactions:
      Balance the carbon atoms
      Balance the hydrogen atoms
      If you need an odd number of Oxygens, double all coefficients
      _____ C4H10 + _____O2 __4___CO2 + _____H2O
      _____ C4H10 + _____O2 __4___CO2 + ___5__H2O
      Need 13 oxygen atoms – so give O2, coefficient of 13 and double all other coefficients
      ___2__ C4H10 + __13___O2 __8___CO2 + __10___H2O
    • Combustion (Complete)
      Some Important Pointers on Complete Combustion
      • Heat is always produced during combustion of hydrocarbons
       exothermic reaction always.
      General Equation:CxHy(g) + (x + y/4) O2(g)  x CO2(g) + (y/2) H2O(l)
    • Combustion (InComplete)
      Some Important Pointers on Complete Combustion
      • When there is insufficient oxygen gas, incomplete combustionoccurs.
      • Note:Incomplete combustion also occurs for larger alkanes
      (e.g candle wax C25H52)
      • Its means that the alkanes is not burnt completely and gives a moresooty flame (orange-yellow in colour) !
      • The black soot is carbon and the yellow flame comes from glowing carbon atoms
      Think Tank Time : Can you suggest some products produced by the incomplete
      combustion besides CO2 & H2O?
      • Carbon Monoxide (CO)
      • Soot (unburnt carbon particles)
    • Combustion (InComplete)
      What Happens If There Is Insufficient Oxygen ?
      The possible balanced chemical equation for the incomplete combustion of methane gas is :
      CH4(g) + O2(g) -> C(s) + 2H2O(g) [Carbon Only]
      2CH4(g) + 3O2(g) -> 2CO(s) + 4H2O(g) [Carbon Monoxide Only]
      4CH4(g) + 5O2(g) ->2CO(s) + 2C(s) 8H2O(g) [Mixture of Both]
    • Substitution Reaction
      Substitution Reactions of Methane (CH4) and Chlorine (Cl2)
    • Substitution Reaction
      What Is It About?
      • Alkanes react with halogens, such as chlorine and bromine, in the presence of ultraviolet light (UV light)
      • For example:
      • Methane reacts with chlorine to form chloromethane and hydrogen chloride gas.
      CH4(g) + Cl2(g) CH3Cl(g) + HCl(g)
      • This is substitution reaction. The hydrogen atom in methane is replaced by chlorine atom.
      UV light
    • Substitution Reaction
      • How does the reaction look like?
      UV light
      • More hydrogen atoms can be replaced with chlorine atoms to produce a mixture of four organic compounds!!
    • Substitution Reaction
      • Writing Out The Entire Sequence Of Reaction..
      • More hydrogen atoms can be replaced with chlorine atoms to produce a mixture of four organic compounds!!
    • Summary
      Today you have learnt about the first part of Organic Chemistry:
      Today’s Lesson: Part 1- Alkanes (saturated molecules)
      Naming Organic Compounds
      Homologous Series
      Structural/ Condensed Formula of Alkanes
      Physical Properties of Alkanes
      Chemical Properties of Alkanes
      Uses of Alkanes and its substituted derivatives
      Next lesson: Part 2-Alkenes(unsaturated molecules)
    • Bunsen Burner Shockwave Flash Animation and Pictures:
      Pictures from Slides 5:
      Pictures from Slides 6:
      Pictures from Slides 8 & 9:
      ‘O’ Level Science Chemistry by Tan Yin Toon pg. 193
      Pictures from Slide 10:
      Pictures from Slide 31: