Presentation on theme: "Chapter 25 “Hydrocarbon Compounds”"— Presentation transcript:
1 Chapter 25 “Hydrocarbon Compounds” ChemistryGolden Valley High SchoolStephen L. Cotton
2 Section 25.1 HydrocarbonsOBJECTIVES:Describe the relationship between number of valence electrons and bonding in carbon.
3 Define and describe alkanes. Section 25.1 HydrocarbonsOBJECTIVES:Define and describe alkanes.
4 Relate the polarity of hydrocarbons to their solubility. Section 25.1 HydrocarbonsOBJECTIVES:Relate the polarity of hydrocarbons to their solubility.
5 Organic Chemistry and Hydrocarbons Organic originally meant chemicals that came from organisms1828 German chemist Friedrich Wohler synthesized urea in a labToday, organic chemistry is the chemistry of virtually all compounds containing the element carbon
6 Friedrich Wohler1800 – 1882Used inorganic substances to synthesize urea, a carbon compound found in urine.This re-defined organic chemistry.
7 Organic Chemistry and Hydrocarbons Over a million organic compounds, with a dazzling array of propertiesWhy so many? Carbon’s unique bonding ability!Let’s start with the simplest of the organic compounds: Hydrocarbons
8 Organic Chemistry and Hydrocarbons Hydrocarbons contain only two elements: 1) hydrogen, & 2) carbonsimplest hydrocarbons called “alkanes”, which contain only carbon to carbon single covalent bonds (CnH2n+2)methane (CH4) with one carbon is the simplest alkane. It is the major component of natural gas
9 Organic Chemistry and Hydrocarbons Carbon has 4 valence electrons, thus forms 4 covalent bondsnot only with other elements, but also forms bonds WITH ITSELF (nonpolar)Ethane (C2H6) is the simplest alkane with a carbon to carbon bond
10 Straight-Chain Alkanes 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.Names of alkanes always will always end with -ane
11 Straight-Chain Alkanes Combined with the -ane ending is a prefix for the number of carbonsTable 25.1, page 745Homologous series- a group of compounds that have a constant increment of changeIn alkanes, it is: -CH2- (methylene)
12 Straight-Chain Alkanes Many alkanes used for fuels: methane, propane, butane, octaneAs 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 Names recommended by IUPAC - the International Union of Pure and Applied Chemistryend with –ane; the root part of the name indicates the # of carbonsWe sometimes still rely on common names, some of which are well-known
14 Naming Straight-Chain Alkanes IUPAC names may be long and cumbersomeCommon 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 Branched-chain means that other elements besides hydrogen may be attached to the carbonhalogens, oxygen, nitrogen, sulfur, and even other carbonsany atom that takes the place of a hydrogen on a parent hydrocarbon is called a substituent, or the branched part
16 Branched-Chain Alkanes A hydrocarbon substituent is called an alkyl group or sometimes radicalsuse 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
17 Branched-Chain Alkanes Rules for naming – go from right to left - page 7481. Longest C-C chain is parent2. Number so branches have lowest #3. Give position number to branch4. Prefix (di, tri) more than one branch5. Alphabetize branches (not prefix)6. Use proper punctuation ( - and , )
19 Branched-Chain Alkanes From the name, draw the structure, in a right-to-left manner:1. Find the parent, with the -ane2. Number carbons on parent3. Identify substituent groups (give lowest number); attach4. Add remaining hydrogens
21 Properties of Alkanes Draw 3-ethylpentane Draw 2,3,4-trimethylhexane Since the electrons are shared equally, the molecule is nonpolarthus, not attracted to wateroil (a hydrocarbon) not soluble in H2O“like dissolves like”
23 Section 25.2 Unsaturated Hydrocarbons OBJECTIVES:Describe the difference between unsaturated and saturated hydrocarbons.
24 Section 25.2 Unsaturated Hydrocarbons OBJECTIVES:Distinguish the structures of alkenes and alkynes.
25 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=CCalled “unsaturated” if they contain double or triple bonds
26 Naming Alkenes Find longest parent that has the double bond in it New ending: -eneNumber the chain, so that the double bond gets the lower numberName and number the substituentsSamples on page 702
27 AlkynesHydrocarbons containing carbon to carbon triple bonds called alkynes(CnH2n-2) C C-Alkynes are not plentiful in natureSimplest is ethyne- common name acetylene (fuel for torches)Table 22.3, p. 703 for boiling pt.
28 Explain why structural isomers have different properties. Section 25.3 IsomersOBJECTIVES:Explain why structural isomers have different properties.
29 Describe the conditions under which geometric isomers are possible. Section 25.3 IsomersOBJECTIVES:Describe the conditions under which geometric isomers are possible.
31 Structural IsomersCompounds that have the same molecular formula, but different molecular structures, are called structural isomersButane and 2-methylpropane (make by breaking Carbon off the end, and making a branch in the middle)Also have different properties, such as b.p., m.p., and reactivity
33 StereoisomersDon’t forget that these structures are really 3-dimensionalstereoisomers- 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 IsomersThere is a lack of rotation around a carbon to carbon multiple bondhas an important structural implicationTwo possible arrangements:1. trans configuration - substituted groups on opposite sides of double bond2. cis configuration - same side
35 Geometric IsomersSubstituted groups are on opposite sides of the double bond (in this case, one is above, the other is below)Trans-2-buteneSubstituted groups are on the same side of the double bond (in this case, both are above)Cis-2-butene
36 Geometric Isomers Trans-2-butene and Cis-2-butene shown on page 754 differ in the geometry of the substituted groups (to double bond)like other structural isomers, have different physical and chemical properties
37 Optical IsomersAsymmetric carbon? C with 4 different groups attached. Conceptual Problem 25.12, p.755Molecules 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 OBJECTIVES:Identify cyclic ring structures.
40 Section 25.4 Hydrocarbon Rings OBJECTIVES:Describe bonding in benzene.
41 Cyclic HydrocarbonsThe two ends of the carbon chain are attached in a ring in a cyclic hydrocarbonsample drawings on page 759named as “cyclo- ____”hydrocarbon compounds that do NOT contain rings are known as aliphatic compounds
42 Aromatic Hydrocarbons A special group of unsaturated cyclic hydrocarbons is known as arenescontain single rings, or groups of ringsalso called “aromatic hydrocarbons”, because of pleasant odorsimplest aromatic is benzene (C6H6)Term “aromatic” applies to materials with bonding like that of benzene
43 Aromatic Hydrocarbons Benzene is a six-carbon ring, with alternating double and single bondsexhibits resonance, due to location of the double and single bonds-p.760Benzene derivatives possible:methylbenzene, 3-phenylhexane, ethylbenzene page 761
44 Aromatic Hydrocarbons Benzene derivatives can have two or more substitutents:1,2-dimethylbenzene1,3-dimethylbenzene1,4-dimethylbenzeneCan use ortho for 1,2; meta for 1,3; and para for 1,4 (page 761)CCCC
45 Section 25.5 Hydrocarbons From Earth’s Crust OBJECTIVES:Identify three important fossil fuels and describe their origins.
46 Section 25.5 Hydrocarbons From Earth’s Crust OBJECTIVES:Describe the composition of natural gas, petroleum, and coal.
47 Section 25.5 Hydrocarbons From Earth’s Crust OBJECTIVES:Describe what happens when petroleum is refined.
48 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 oceansNatural gas is an important source of alkanes of low molecular mass
49 Natural Gas Natural gas is typically: 80% methane, 10% ethane, 4% propane, and 2% butane with the remainder being nitrogen and higher molar mass hydrocarbonsalso contains a small amount of He, and is one of it’s major sources
50 Natural GasNatural gas is prized for combustion, because with adequate oxygen, it burns with a hot, clean blue flame:CH4 + 2O2 CO2 + 2H2O + heatIncomplete burning has a yellow flame, due to glowing carbon parts, as well as making carbon monoxide
51 PetroleumThe compounds found in petroleum (or crude oil) are more complex than those in natural gasUsually straight-chain and branched-chain alkanes, with some aromatic compounds alsoCrude oil must be refined (separated) before being used
52 PetroleumIt 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 keroseneinvolves catalyst and heatstarts materials for plastics and paints
53 CoalFrom 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
54 Coal2. Lignite- peat left in the ground longer, loses it’s fibrous texture, and is also called brown coalharder than peat; higher C content (50%); still has high water content3. 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 sourceCoal may be found close to the surface (strip-mined), or deep within the earthPollutants from coal are common; soot and sulfur problems
56 Note the man standing beside it BIG BRUTUSDragline used to remove the overburden of a strip mining coal field near West Mineral, KansasNote the man standing beside it
57 Coal Coal may be distilled for many products coal gas, coal tar, coke, and ammoniafurther distilled into benzene, toluene, naphthalene, phenol- the aromaticsCoke is almost pure carbon; produces intense heat and little or no smoke, thus used in industrial processes