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Chapter 22 “Hydrocarbon Compounds” PowerPoint PPT Presentation


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Chapter 22 “Hydrocarbon Compounds”. Pre-AP Chemistry Charles Page High School Stephen L. Cotton. (C 4 H 10 ). Section 22.1 Hydrocarbons. OBJECTIVES: Describe the relationship between number of valence electrons and bonding in carbon . Section 22.1 Hydrocarbons. OBJECTIVES:

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Chapter 22 hydrocarbon compounds l.jpg

Chapter 22“Hydrocarbon Compounds”

Pre-AP Chemistry

Charles Page High School

Stephen L. Cotton

(C4H10)


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Section 22.1Hydrocarbons

  • OBJECTIVES:

    • Describe the relationship between number of valence electrons and bonding in carbon.


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Section 22.1Hydrocarbons

  • OBJECTIVES:

    • Define and describe alkanes.


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Section 22.1Hydrocarbons

  • OBJECTIVES:

    • Relate the polarity of hydrocarbons to their solubility.


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Organic Chemistry and Hydrocarbons

  • “Organic” originally referred to any chemicals that came from organisms

  • 1828 - German chemist Friedrich Wohler synthesized urea in a lab

  • Today, organic chemistry is the chemistry of virtually all compounds containing the element carbon


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  • Friedrich Wohler

  • 1800 – 1882

  • Used inorganic substances to synthesize urea, a carbon compound found in urine.

  • This re-defined organic chemistry.


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Organic Chemistry and Hydrocarbons

  • Over a million organic compounds, with a dazzling array of properties

  • Why so many? Carbon’s unique bonding ability!

  • Let’s start with the simplest of the organic compounds. These are the Hydrocarbons


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Organic Chemistry and Hydrocarbons

  • Hydrocarbons contain only two elements: 1) hydrogen, and 2) carbon

    • simplest hydrocarbons called “alkanes”, which contain only carbon to carbon singlecovalent bonds (CnH2n+2)

    • methane (CH4) with one carbon is the simplest alkane. It is the major component of natural gas


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Organic Chemistry and Hydrocarbons

  • Review structural formulas - p.694

  • Carbon has 4 valence electrons, thus forms 4 covalent bonds

    • not only with other elements, but also forms bonds WITH ITSELF (nonpolar)

  • Ethane (C2H6) is the simplest alkane with a carbon to carbon bond


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Straight-Chain Alkanes

  • Straight-chain alkanes contain any number of carbon atoms, one after the other, in a chain pattern - meaning one linked to the next (not always straight)

    C-C-C C-C-C-C etc.

  • Names of alkanes always will always end with -ane


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Straight-Chain Alkanes

  • Combined with the -ane ending is a prefix for the number of carbons

    • Table 22.1, page 695

  • Homologous series- a group of compounds that have a constant increment of change

  • In alkanes, it is: -CH2- (methylene)


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Straight-Chain Alkanes

  • Many alkanes used for fuels: methane, propane, butane, octane

  • As the number of carbons increases, so does the boiling and melting pt.

    • The first 4 are gases; #5-15 are liquids; higher alkanes are solids

  • Condensed structural formulas? Note examples on page 696


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Naming Straight-Chain Alkanes

  • Names recommended by IUPAC - the International Union of Pure and Applied Chemistry

    • end with –ane; the root part of the name indicates the # of carbons

  • We sometimes still rely on common names, some of which are well-known


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Naming Straight-Chain Alkanes

  • IUPAC names may be long and cumbersome

  • Common names may be easier or more familiar, but usually do not describe the chemical structure!

    • Methane is natural gas or swamp gas


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Branched-Chain Alkanes

  • Branched-chain means that other elements besides hydrogen may be attached to the carbon

    • halogens, oxygen, nitrogen, sulfur, and even other carbons

    • any atom that takes the place of a hydrogen on a parent hydrocarbon is called a substituent, or the branchedpart


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Branched-Chain Alkanes

  • A hydrocarbon substituent is called an alkyl group or sometimes radicals

    • use the same prefixes to indicate the number of carbons, but -ane ending is now -yl such as: methyl, ethyl, propyl, etc.

  • Gives much more variety to the organic compounds


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Branched-Chain Alkanes

  • Rules for naming – go from right to left - page 698

    1. Longest C-C chain is parent

    2. Number so branches have lowest #

    3. Give position number to branch

    4. Prefix (di, tri) more than one branch

    5. Alphabetize branches (not prefix)

    6. Use proper punctuation ( - and , )


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- Page 699


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Branched-Chain Alkanes

  • From the name, draw the structure, in a right-to-left manner:

    1. Find the parent, with the -ane

    2. Number carbons on parent

    3. Identify substituent groups (give lowest number); attach

    4. Add remaining hydrogens


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- Page 700


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Alkanes

  • Draw 3-ethylpentane

  • Draw 2,3,4-trimethylhexane

  • Since the electrons are shared equally, the molecule is nonpolar

    • thus, not attracted to water

    • oil (a hydrocarbon) not soluble in H2O

    • “like dissolves like”


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Section 22.2Unsaturated Hydrocarbons

  • OBJECTIVES:

    • Describe the difference between unsaturated and saturated hydrocarbons.


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Section 22.2Unsaturated Hydrocarbons

  • OBJECTIVES:

    • Distinguish the structures of alkenes and alkynes.


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Alkenes

  • Multiple bonds can also exist between the carbon atoms

  • Hydrocarbons containing carbon to carbon double bonds are called alkenes(CnH2n) C=C C-C=C

  • Called “unsaturated” if they contain double or triple bonds


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Naming Alkenes

  • Find longest parent that has the double bond in it

  • New ending: -ene

  • Number the chain, so that the double bond gets the lower number

  • Name and number the substituents

  • Samples on page 702


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Alkynes

  • Hydrocarbons containing carbon to carbon triple bonds are called alkynes

    (CnH2n-2) -C C-

  • Alkynes are not plentiful in nature

  • Simplest is ethyne- common name acetylene (fuel for torches)

  • Table 22.3, p. 703 for boiling pt.

ethyne


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Section 22.3Isomers

  • OBJECTIVES:

    • Explain why structural isomers have different properties.


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Section 22.3Isomers

  • OBJECTIVES:

    • Describe the conditions under which geometric isomers are possible.


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Section 22.3Isomers

  • OBJECTIVES:

    • Identify optical isomers.


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Structural Isomers

  • Compounds that have the same molecular formula, but different molecular structures, are called structural isomers

  • Butane and 2-methylpropane (made by breaking carbon off the end, and making it a branch in the middle)

  • Also have different properties, such as b.p., m.p., and reactivity


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Structural Isomers of Butane, C4H10


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Stereoisomers

  • Don’t forget that these structures are really 3-dimensional

  • stereoisomers- molecules of the same molecular structure that differ only in the arrangement of the atoms in space. Two types are a) geometric and b) optical


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Geometric Isomers

  • There is a lack of rotation around a carbon to carbon multiple bond

    • has an important structural implication

    • Two possible arrangements:

      1.trans configuration - substituted groups on opposite sides of double bond

      2. cisconfiguration - same side


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Geometric Isomers

Substituted groups are on opposite sides of the double bond (in this case, one is above, the other is below)

Trans-2-butene

Substituted groups are on the same side of the double bond (in this case, both are above)

Cis-2-butene


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Geometric Isomers

  • Trans-2-butene and Cis-2-butene shown on page 705

  • differ in the geometry of the substituted groups (to double bond)

  • like other structural isomers, have different physical and chemical properties ( note page 705-middle)


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Optical Isomers

  • Asymmetric carbon? C with 4 different groups attached. Conceptual Problem 22.4, p.706

  • Molecules containing asymmetric carbons have “handedness”, and exist as stereoisomers.

    • Figure 22.9, page 705


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Optical Isomers, and these will each show an asymetric carbon (4 different branches attached)

The asymetric carbon


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Section 22.4Hydrocarbon Rings

  • OBJECTIVES:

    • Identify cyclic ring structures.


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Section 22.4Hydrocarbon Rings

  • OBJECTIVES:

    • Describe bonding in benzene.


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Cyclic Hydrocarbons

  • The two ends of the carbon chain are attached in a ring in a cyclic hydrocarbon

    • sample drawings on page 709

    • named as “cyclo- ____”

  • hydrocarbon compounds that do NOT contain rings are known as aliphatic compounds


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Aromatic Hydrocarbons

  • A special group of unsaturated cyclic hydrocarbons is known as arenes

    • contain single rings, or groups of rings

    • also called “aromatic hydrocarbons”, because of pleasant odor

    • simplest aromatic is benzene (C6H6)

    • Term “aromatic” applies to materials with bonding like that of benzene


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Aromatic Hydrocarbons

  • Benzene is a six-carbon ring, with alternating double and single bonds

    • exhibits resonance, due to location of the double and single bonds-p.710

  • Benzene derivatives possible:

    • methylbenzene, 3-phenylhexane, ethylbenzene (top page 711)


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Aromatic Hydrocarbons

  • One derivative of Benzene is called phenylethene, or commonly named STYRENE.

  • Foamed styrene is trademarked by Dow Chemical as “styrofoam”

  • Other manufacturers items usually just called “foam cups”

CH2

CH


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Aromatic Hydrocarbons

  • Benzene derivatives can have two or more substitutents:

    • 1,2-dimethylbenzene

    • 1,3-dimethylbenzene

    • 1,4-dimethylbenzene

  • Can use ortho for 1,2; meta for 1,3; and para for 1,4 (page 711)

C

C

C

C


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Section 22.5Hydrocarbons From Earth’s Crust

  • OBJECTIVES:

    • Identify three important fossil fuels and describe their origins.


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Section 22.5Hydrocarbons From Earth’s Crust

  • OBJECTIVES:

    • Describe the composition of natural gas, petroleum, and coal.


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Section 22.5Hydrocarbons From Earth’s Crust

  • OBJECTIVES:

    • Describe what happens when petroleum is refined.


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Natural Gas

  • Fossil fuels provide much of the world’s energy

  • Natural gas and petroleum contain mostly the aliphatic (or straight-chain) hydrocarbons – formed from marine life buried in sediment of the oceans

  • Natural gas is an important source of alkanes of low molecular mass


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Natural Gas

  • Natural gas is typically:

    • 80% methane, 10% ethane, 4% propane, and 2% butane with the remainder being nitrogen and higher molar mass hydrocarbons

    • also contains a small amount of He, and is one of it’s major sources


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Natural Gas

  • Natural gas is prized for combustion, because with adequate oxygen, it burns with a hot, clean blue flame:

    • CH4 + 2O2 CO2 + 2H2O + heat

  • Incomplete burning has a yellow flame, due to glowing carbon parts, as well as making carbon monoxide


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Petroleum

  • The compounds found in petroleum (or crude oil) are more complex than those in natural gas

  • Usually straight-chain and branched-chain alkanes, with some aromatic compounds also

  • Crude oil must be refined (separated) before being used


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Petroleum

  • It is separated by distillation into fractions, according to boiling pt.

  • Fractions containing higher molar mass can be “cracked” into more useful shorter chain components, such as gasoline and kerosene

    • involves catalyst and heat

    • starts materials for plastics and paints


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Coal

  • From huge fern trees and mosses decaying millions of years ago under great pressure of rocks / soil.

  • Stages in coal formation:

    1. Peat- soft, fibrous material much like decayed garden refuse; high water content. After drying will make a low-cost, smoky fuel


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Coal

2. Lignite- peat left in the ground longer, loses it’s fibrous texture, and is also called brown coal

  • harder than peat; higher C content (50%); still has high water content

    3. Bituminous, or soft coal- formed after more time; lower water content, higher C content (70-80%)


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Coal

4. Anthracite, or hard coal

  • carbon content exceeding 80%, making it an excellent fuel source

  • Coal may be found close to the surface (strip-mined), or deep within the earth

  • Pollutants from coal are common; soot and sulfur problems


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    BIG BRUTUS

    Dragline used to remove the overburden of a strip mining coal field near West Mineral, Kansas.

    Note the size of the man standing next to it.


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    Coal

    • Coal may be distilled for many products

      • coal gas, coal tar, coke, and ammonia

      • further distilled into benzene, toluene, naphthalene, phenol- the aromatics

      • Coke is almost pure carbon; produces intense heat and little or no smoke, thus used in industrial processes


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    End of Chapter 22


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