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Chapter 22 Hydrocarbon Compounds
Organic Chemistry and Hydrocarbons
Organic originally meant chemicals that came from organisms
1828 German chemist Friedrich Wohler synthesized urea in the lab
Today, organic chemistry is the chemistry of virtually all compounds containing the element carbon
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: Hydrocarbons
Organic Chemistry and Hydrocarbons
Hydrocarbons contain only two elements: hydrogen and carbon– simplest hydrocarbons called
alkanes, which contain only single covalent bonds
– methane (CH4) with one carbon is the simplest alkane. It is the major component of natural gas
Models of Methane
Organic Chemistry and Hydrocarbons
Review structural formula- p. 698 Carbon has 4 valence electrons,
thus forms 4 covalent bonds– not only with other elements, but also
forms bonds WITH ITSELF.
Ethane (C2H6) is the simplest alkane with a carbon to carbon bond
Straight-Chain Alkanes
Straight-chain alkanes contain any number of carbon atoms, one after the other, in a chain -meaning one linked to the nextC-C-C C-C-C-C etc.
Names of alkanes will always end with -ane
Straight-Chain Alkanes
Combined with the -ane ending is a prefix for the number of carbons– Table 22.1, page 700
Homologous series- a group of compounds that have a constant increment of change
In alkanes, it is: -CH2-
Alkane Hydrocarbons
Alkane Prefixes – The root indicates the
number of carbon atoms
Name Molecular Form
Methane CH4
Ethane C2H6
Propane C3H8
Butane C4H10
Pentane C5H12
Hexane C6H14
Heptane C7H16
Octane C8H18
Nonane C9H20
Decane C10H22
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 702
Alkane Melting and Boiling Points
Functional Groups
Most organic chemistry involves replacing one or more of the hydrogen atoms with a ‘substituent group’– Groups often contain C, O, N, S, or P– They are also called “functional groups”-
the chemically functional part of the molecule. They change the properties or function of the molecule.
AlcoholsAlcohols - a class of organic
compounds with an -OH group–The -OH functional group in
alcohols is called a “hydroxyl” group; thus R-OH is the formula
How is this different from the hydroxide ion with basics? (covalent bonding with carbon- not ionic with a metal such as sodium)
Methanol Structure
Ethanol Ball and Stick
Alcohols Both IUPAC and common names For IUPAC:
–drop the -e ending of the parent alkane name; add ending of -ol, number the position of -OH
–parent is the longest chain that contains the carbon with the hydroxyl attached.
AlcoholsCommon names:
–similar to halocarbons, meaning name the alkyl group followed by the word ‘alcohol’
–One carbon alcohol = methyl alcohol
Properties of Alcohols Denatured alcohol- means it has
been made poisonous by the addition of other chemicals, often methyl alcohol (methanol, or wood alcohol). As little as 10 mL of methanol has been known to cause permanent blindness, and 30 mL has resulted in death!!!
Alkenes Multiple bonds can also exist
between the carbon atoms Hydrocarbons containing carbon to
carbon double bonds are called alkenes C=C C-C=C
Called “unsaturated” hydrocarbons if they contain double or triple bonds
Alkynes Hydrocarbons containing carbon to
carbon triple bonds called alkynes
-C C- Alkynes are not plentiful in nature Simplest is ethyne- common name
acetylene (fuel for torches) Table 22.5, page 715 for b.p. and m.p.
Section 22.5Hydrocarbons from the Earth
OBJECTIVES:
–Identify three important fossil fuels and describe their origins.
Natural Gas
Fossil fuels provide much of the world’s energy
Natural gas and petroleum contain mostly aliphatic (straight-chain) hydrocarbons
Natural gas is an important source of alkanes of low molecular mass
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, that is recovered and used in various industries, including balloons
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
Insufficient burning has a yellow flame, due to glowing carbon parts, as well as making carbon monoxide
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
Petroleum Fractional Distillation
Crude Oil Components
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– starter materials for plastics and
paints
Petroleum Cracking
Coal From huge fern trees and mosses
decaying millions of years ago under great pressure
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
Coal2. 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%)
Coal4. 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
Scrubbing Sulfur From Coal
Coal Coal may be distilled for many
products– coal gas, coal tar, coke, and ammonia
– further distilled into benzene, toluene, naphthalene, phenol, and pitch
– Coke is almost pure carbon; produces intense heat and little or no smoke, thus used in industrial processes