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Chapter 25 “Hydrocarbon Compounds” Chemistry Golden Valley High School Stephen L. Cotton.

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Presentation on theme: "Chapter 25 “Hydrocarbon Compounds” Chemistry Golden Valley High School Stephen L. Cotton."— Presentation transcript:

1 Chapter 25 “Hydrocarbon Compounds” Chemistry Golden Valley High School Stephen L. Cotton

2 Section 25.1 Hydrocarbons l OBJECTIVES: –Describe the relationship between number of valence electrons and bonding in carbon.

3 Section 25.1 Hydrocarbons l OBJECTIVES: –Define and describe alkanes.

4 Section 25.1 Hydrocarbons l OBJECTIVES: –Relate the polarity of hydrocarbons to their solubility.

5 Organic Chemistry and Hydrocarbons l Organic originally meant chemicals that came from organisms l 1828 German chemist Friedrich Wohler synthesized urea in a lab l Today, organic chemistry is the chemistry of virtually all compounds containing the element carbon

6 Friedrich Wohler 1800 – 1882 Used inorganic substances to synthesize urea, a carbon compound found in urine. This re-defined organic chemistry.

7 Organic Chemistry and Hydrocarbons l Over a million organic compounds, with a dazzling array of properties l Why so many? Carbon’s unique bonding ability! l Let’s start with the simplest of the organic compounds: Hydrocarbons

8 Organic Chemistry and Hydrocarbons l Hydrocarbons contain only two elements: 1) hydrogen, & 2) carbon –simplest hydrocarbons called “alkanes”, which contain only carbon to carbon single covalent bonds (C n H 2n+2 ) –methane (CH 4 ) with one carbon is the simplest alkane. It is the major component of natural gas

9 Organic Chemistry and Hydrocarbons l Carbon has 4 valence electrons, thus forms 4 covalent bonds –not only with other elements, but also forms bonds WITH ITSELF (nonpolar) l Ethane (C 2 H 6 ) is the simplest alkane with a carbon to carbon bond

10 Straight-Chain Alkanes l Straight-chain alkanes contain any number of carbon atoms, one after the other, in a chain - meaning one linked to the next (not always straight) C-C-C C-C-C-C etc. l Names of alkanes always will always end with -ane

11 Straight-Chain Alkanes l Combined with the -ane ending is a prefix for the number of carbons  Table 25.1, page 745 l Homologous series- a group of compounds that have a constant increment of change l In alkanes, it is: -CH 2 - (methylene)

12 Straight-Chain Alkanes l Many alkanes used for fuels : methane, propane, butane, octane l 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

13 Naming Straight-Chain Alkanes l 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 l We sometimes still rely on common names, some of which are well-known

14 Naming Straight-Chain Alkanes l IUPAC names may be long and cumbersome l Common names may be easier or more familiar, but usually do not describe the chemical structure! –Methane is natural gas or swamp gas

15 Branched-Chain Alkanes l 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 branched part

16 Branched-Chain Alkanes l 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. l Gives much more variety to the organic compounds

17 Branched-Chain Alkanes l Rules for naming – go from right to left - page 748 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, )

18 - Page 699

19 Branched-Chain Alkanes l 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

20 - Page 700

21 Properties of Alkanes l Draw 3-ethylpentane l Draw 2,3,4-trimethylhexane l Since the electrons are shared equally, the molecule is nonpolar –thus, not attracted to water –oil (a hydrocarbon) not soluble in H 2 O –“like dissolves like”

22 Quiz Draw. l 2,3 diethyl pentane l 3,3, 4 tri-methyl octane l 2,3 ethyl, methyl hexane Name C C C-C-C-C-C-C

23 Section 25.2 Unsaturated Hydrocarbons l OBJECTIVES: –Describe the difference between unsaturated and saturated hydrocarbons.

24 Section 25.2 Unsaturated Hydrocarbons l OBJECTIVES: –Distinguish the structures of alkenes and alkynes.

25 Alkenes l Multiple bonds can also exist between the carbon atoms l Hydrocarbons containing carbon to carbon double bonds are called alkenes (C n H 2n ) C=C C-C=C l Called “unsaturated” if they contain double or triple bonds

26 Naming Alkenes l Find longest parent that has the double bond in it l New ending: -ene l Number the chain, so that the double bond gets the lower number l Name and number the substituents l Samples on page 702

27 Alkynes l Hydrocarbons containing carbon to carbon triple bonds called alkynes (C n H 2n-2 ) -C C- l Alkynes are not plentiful in nature l Simplest is ethyne- common name acetylene (fuel for torches) l Table 22.3, p. 703 for boiling pt.

28 Section 25.3 Isomers l OBJECTIVES: –Explain why structural isomers have different properties.

29 Section 25.3 Isomers l OBJECTIVES: –Describe the conditions under which geometric isomers are possible.

30 Section 25.3 Isomers l OBJECTIVES: –Identify optical isomers.

31 Structural Isomers l Compounds that have the same molecular formula, but different molecular structures, are called structural isomers l Butane and 2-methylpropane (make by breaking Carbon off the end, and making a branch in the middle) l Also have different properties, such as b.p., m.p., and reactivity

32 Structural Isomers of Butane, C 4 H 10

33 Stereoisomers l Don’t forget that these structures are really 3-dimensional l 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

34 Geometric Isomers l 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. cis configuration - same side

35 Substituted groups are on opposite sides of the double bond (in this case, one is above, the other is below) Substituted groups are on the same side of the double bond (in this case, both are above) Geometric Isomers Trans-2-butene Cis-2-butene

36 Geometric Isomers l Trans-2-butene and Cis-2-butene shown on page 754 l differ in the geometry of the substituted groups (to double bond) l like other structural isomers, have different physical and chemical properties

37 Optical Isomers l Asymmetric carbon? C with 4 different groups attached. Conceptual Problem 25.12, p.755 l Molecules containing asymmetric carbons have “handedness”, and exist as stereoisomers.

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

39 Section 25.4 Hydrocarbon Rings l OBJECTIVES: –Identify cyclic ring structures.

40 Section 25.4 Hydrocarbon Rings l OBJECTIVES: –Describe bonding in benzene.

41 Cyclic Hydrocarbons l The two ends of the carbon chain are attached in a ring in a cyclic hydrocarbon –sample drawings on page 759 –named as “cyclo- ____” l hydrocarbon compounds that do NOT contain rings are known as aliphatic compounds

42 Aromatic Hydrocarbons l 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 (C 6 H 6 ) –Term “aromatic” applies to materials with bonding like that of benzene

43 Aromatic Hydrocarbons l Benzene is a six-carbon ring, with alternating double and single bonds –exhibits resonance, due to location of the double and single bonds-p.760 l Benzene derivatives possible: –methylbenzene, 3-phenylhexane, ethylbenzene page 761

44 Aromatic Hydrocarbons l Benzene derivatives can have two or more substitutents: –1,2-dimethylbenzene –1,3-dimethylbenzene –1,4-dimethylbenzene l Can use ortho for 1,2; meta for 1,3; and para for 1,4 (page 761) C C C C

45 Section 25.5 Hydrocarbons From Earth’s Crust l OBJECTIVES: –Identify three important fossil fuels and describe their origins.

46 Section 25.5 Hydrocarbons From Earth’s Crust l OBJECTIVES: –Describe the composition of natural gas, petroleum, and coal.

47 Section 25.5 Hydrocarbons From Earth’s Crust l OBJECTIVES: –Describe what happens when petroleum is refined.

48 Natural Gas l Fossil fuels provide much of the world’s energy l Natural gas and petroleum contain mostly the aliphatic (or straight-chain) hydrocarbons – formed from marine life buried in sediment of the oceans l Natural gas is an important source of alkanes of low molecular mass

49 Natural Gas l 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

50 Natural Gas l Natural gas is prized for combustion, because with adequate oxygen, it burns with a hot, clean blue flame: –CH 4 + 2O 2  CO 2 + 2H 2 O + heat l Incomplete burning has a yellow flame, due to glowing carbon parts, as well as making carbon monoxide

51 Petroleum l The compounds found in petroleum (or crude oil) are more complex than those in natural gas l Usually straight-chain and branched-chain alkanes, with some aromatic compounds also l Crude oil must be refined (separated) before being used

52 Petroleum l It is separated by distillation into fractions, according to boiling pt. l 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

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

54 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%)

55 Coal 4. Anthracite, or hard coal –carbon content exceeding 80%, making it an excellent fuel source l Coal may be found close to the surface (strip-mined), or deep within the earth l Pollutants from coal are common; soot and sulfur problems

56 BIG BRUTUS Dragline used to remove the overburden of a strip mining coal field near West Mineral, Kansas Note the man standing beside it

57 Coal l 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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