Hydrocarbons

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Hydrocarbons

• Chapter 8

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What is carbon chemistry?

• Compounds containing Carbon make up 90 of all
  chemicals and form the basis of living things
• Organic chemistry is the study of Carbon
  compounds

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How does Carbon form so many compounds?

• The electronic configuration of carbon is
  1s22s22p2.
• It can form a wide variety of compounds because
• each carbon atom has four valence electrons, all
  available for bonding with other atoms
• a carbon atom can form strong covalent bonds with
  other carbon atoms
• bonds between carbon atoms can be single or
  multiple.

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Hydrocarbons

• Compounds made up of Hydrogen and Carbon are
  known as Hydrocarbons
• Hydrocarbons can be classified into several
  series or families
• The first series is known as the alkanes

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Alkanes

• Are a family that consist of carbon and hydrogen
  only
• They contain only single bonds
• CnH2n2
• Compounds that differ only by CH2- belong to the
  same homologous series
• Compounds of the same homologous series share the
  similar chemical properties

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Representing Alkanes

• We use structural formulas to represent
  hydrocarbons
• You will notice that each carbon atom
• forms a single covalent bond to four other atoms
• each hydrogen atom forms a single covalent bond
  to one carbon atom
• the four atoms bonded to each carbon atom are
  arranged in a tetrahedral manner around the
  carbon.

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Structural Isomers

• When we come to draw a structural formula for
  C4H10, however, there are two possible
  arrangements that satisfy the bonding
  requirements of each of the four carbon atoms and
  ten hydrogen atoms

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Structural Isomers

• These two compounds are structural isomers. That
  means that they have the same molecular formula
  (C4H10) but a different
• arrangement of their atoms.
• Structural isomers have similar chemical
  properties but differ in some physical properties
  such as melting and boiling temp.

As molecules become larger, the number of
possible arrangements of atoms increases rapidly.
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Saturated Hydrocarbons

• The alkanes are known as saturated hydrocarbons.
• Because there are only single bonds between
  carbon atoms, they are saturated with hydrogen
  atoms.
• Carbon and hydrogen can also form families of
  compounds in which there are double or triple
  bonds between carbon atoms. These compounds are
  unsaturated as they do not contain the maximum
  number of H atoms.

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Naming Alkanes

• Alkanes use the prefix relevant to the number of
  Carbons, and ends in ane.
• Four things you may be asked for
• Name the compound
• Write the molecular formula
• Draw the Structural formula
• Write the condensed structural formula
  (semi-structural)

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Alkenes

• The alkenes form a new homologous series. Their
  members differ by -CH2- and contain a single
  double bond between two carbon atoms and share
  similar chemical properties.
  
• CnH2n
• Alkenes are unsaturated as they contain less than
  the maximum amount of Hydrogens possible. They
  are named using the same prefix and end in ene.
• Isomers exist in Alkenes as well. Isomers can be
  branched, straight chain or even a different
  position of the double bond.

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Your Turn

• Complete the Handout
• Name the alkanes
• Draw the Structural formula
• Write the semi-structural (condensed) formula
• Write the molecular formula
• Chapter 8 Review Questions
• Q 2, 3, 4, 5, 6
• Complete the second handout of challenge
  questions
• Dont forget SACT due next Wednesday!!
• Check the blog and keep up to date!!

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Naming Organic Compounds

• IUPAC (International Union of Pure and Applied
  Chemisty) created a common set of naming rules

• Rules
• Determine the longest chain of carbon atoms
• Determine which end is nearest to a branch,
  double bond or triple bond
• Number the carbon atoms from the end chosen
• Name any branches first with the ending yl, then
  the longest chain, then any single or double bond
• When two or more branches occur on the same
  carbon atom, the number of the carbon atom is
  indicated for each branch
• When two or more identical branches occur on
  different carbon atoms, the prefixes di, tri and
  tetra are used
• Avoid the common errors
• Not identifying the longest chain
• Not listing the side branches in alphabetical
  answer
• Omitting the prefixes di, tri and tetra

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Naming Organic Compounds

• There are a set of rules used to name carbon
  compounds to distinguish between different
  isomers
• In the systematic naming of straight-chain
  hydrocarbons, the first part of the name refers
  to the number of carbon atoms in one molecule
• The name of the hydrocarbon ends in
• ane if all carbon-to-carbon bonds are single
  bonds
• ene if one of the carbon-to-carbon bonds is a
  double bond
• eyne if one of the carbon-to-carbon bonds is a
  triple bond

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Example - Naming straight chain alkenes

• To name straight-chain alkenes, first number the
  carbon atoms in the chain, starting at the end
  that will give the first carbon atom involved in
  the double bond the smallest number possible.
• The numbering of the chain starts at this end and
  the isomer is named according to the first carbon
  atom involved in the double bond.

But-2-ene
But-1-ene
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Branched Hydrocarbons

• An alkyl group most often forms a branch in a
  branched-chain hydrocarbon.
• An alkyl group is an alkane molecule less one
  hydrogen atom and is named after the alkane from
  which it is derived. For example, CH3 is a
  methyl group,

• Systematic naming requires us to
• identify the longest continuous chain of carbon
  atoms in the molecule and the series the molecule
  belongs to (alkane/alkene/alkyne)
• identify the side group that forms the branch in
  the chain
• number the carbon atoms from one of the ends of
  the longest carbon chain so that the side group
  is attached to the carbon atom with the smallest
  number possible.

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Branched Hydrocarbons Have a go
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Your Turn practice makes perfect!

• Review Questions
• 1. Chapter 8
• Q7
• Q8 (draw as well as name each of these)
• 2. Write the structural formula for
• a) hex-2-ene b) 2-methylpropene c) 2-pentyne
• d) 4-methylpent-2-ene e) 2,4-dimethylhexane
• f) 3,3-dimethylpentane g) 3-ethyl-2,4-dimethylocta
  ne
• h)3-ethylheptane i) 4-ethyl-3-methylhex-2-ene
• j) 3-ethyl-4,5-dipropyloctane

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Functional Groups

• The majority of carbon compounds contain other
  elements in addition to hydrogen.
• Taking an alkane and replacing a hydrogen atom
  with another atom or group of atoms changes the
  chemical properties of the compound.
• An atom or group of atoms that influence the
  properties of the compounds forming a homologous
  series is known as a functional group

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Hydroxyl group - OH

• Alcohols have the functional group OH.
• A functional group is a group of atoms that gives
  the molecule unique chemical properties.
• Molecules with the hydroxyl group (OH) are very
  soluble in water, depending on their molecular
  size.
• A H atom is replaced by an OH group
• The last part of the name is replaced with an
  ol
• Methanol Butanol

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Carboxyl group - COOH

• Carboxylic acids have the functional group COOH.
• Molecules with the carboxyl functional group
  (COOH) are known as organic acids. They dissolve
  in water to form acidic solutions.
• The COOH group is made up
  of
• 2 H atoms are replaced by COOH group
• The last part of the name becomes -anoic acid
• Propanoic Acid Ethanoic Acid

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Halogens - (Cl, Br, I, F)

• Cl chloroalkanes Br - Bromoalkanes
• F Fluoroalkanes I - Idoalkanes
• A H atom is replaced by a Halogen
• The first part of the halogen is said in front of
  the alkane
• Chloroethane 2-Bromopropane

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Physical Properties

• As the number of carbon atoms increases, members
  of a homologous series show a gradual change in
  their physical properties.
• Compounds with smaller molecules are more
  volatile than larger molecules
• Less energy is needed to break bonds of smaller
  molecules
• Smaller molecules have a lower viscosity
• The boiling temperature increases as molecules
  get larger
• This is true for Alkanes and Alkenes.
• If an alkane and alkene have the same number of
  carbons then they will have a similar boiling
  temp, although an alkenes will be slightly lower.

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Physical Properties WHY?

• The bonding within hydrocarbons is covalent
  (strong), however, hydrocarbons are non-polar.
  The forces between molecules are dispersion
  forces which increase in strength as the molecule
  gets bigger.
• More energy is required to overcome the
  dispersion forces between larger hydrocarbon
  molecules, so a higher temperature is required to
  boil
• Volatility (tendency to evaporate) The stronger
  the dispersion forces between molecules in the
  liquid state, the lower the tendency for the
  liquid to evaporate and so the lower the
  volatility.
• The higher viscosity of the longer-chain
  hydrocarbons is due to the tendency of longer
  molecules to become tangled together

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Chemical Properties of Alkanes

• The most significant reaction of alkanes for our
  society is combustion.
• Alkanes burn in oxygen, releasing large
  quantities of energy.
• If the supply of oxygen is sufficient, the
  products of the reaction are carbon dioxide and
  water.
• We use the energy released by the combustion of
  alkanes as a source of heat, to produce
  electricity for domestic and industrial use and
  in transportation.

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Combustion Reactions
Dont forget to add in the states (g, aq, l)