1 - Introduction - Alkanes Mr. ShieldsRegents Chemistry U16 L01

2 Organic Chemistry Organic Chemistry involves the study of Carbon based compounds of which there are millions and many more yet to be made Much more “diversity” than found in inorganic compounds What are some examples of Carbon Based compounds? –Petrochemicals- Biochemicals –Dyes- Polymers –Pharmaceuticals- Life

3 Source The source of almost all organic compounds today is petroleum –Crude oil Through Synthesis hydrocarbons can be further modified into other organic compounds Petroleum (crude oil) is first separted into several different categories at refineries Separation at refineries is a distillation process based on BP (mol. Wt.)

4 Why so many C compounds? Covalent.Carbon atoms can bond with other carbon atoms in chains. These bonds are Covalent. Since Carbon has 4 unpaired electrons it can form 4 covalent bonds. C

5 Carbons ability to form 4 covalent bonds, even with itself, leads to carbons ability to form millions of different compounds, some simple some very complex. Formation of Carbons 4 covalent bonds

6 Properties of Covalent Substances Molecular Compounds Covalent compounds are Molecular Compounds What do we mean by “Molecular” and What kind of properties do they have? Low melting points & boiling points Poor conductors of heat & electricity Solids tend to be soft Can not be worked (not malleable) May be Polar or nonpolar Non-polar is not soluable in water Polar may be slightly sol. to sol. in water Non-polar will dissolve in non-polar solvents React more slowly than ionic compounds

7 Structural Formulas Shows kind & number of atoms and how they are bonded together. They are 2-D drawings of 3-D objects so structural formulas aren’t totally realistic. H H–C–H H

8 Structural Formulas “–” A single line represents one pair of“–” A single line represents one pair of electrons (a single bond). electrons (a single bond). “=“ A double line represents two pairs of“=“ A double line represents two pairs of electrons (a double bond). electrons (a double bond). “  ” A triple line represents three pairs of“  ” A triple line represents three pairs of electrons (a triple bond). electrons (a triple bond).

9 Condensed Structural Formulas These formulas show kind & number of atoms as well as some information regarding what atoms are joined to what atoms but not how. They don’t depict bonds Examples: CH 4, CH 3 OH, CH 3 Cl, CH 2 Cl 2, CH 3 CH 2 CH 2 CH 3, CH 3 COOH No information given on how these oxygen are bonded to this carbon

10 Molecular Formulas These formulas show kind & number of atoms but not necessarily any other informationThese formulas show kind & number of atoms but not necessarily any other information Condensed Structural formula Examples: CH 3 OH, CH 3 CH 2 CH 2 CH 3, CH 3 COOH Molecular formula Becomes: CH 4 O, C 4 H 10, C 2 H 4 O 2

11 Molecular Shape When carbon is bonded to 4 other atoms carbon is at the center of a tetrahedron and the 4 other atoms are located at the corners.When carbon is bonded to 4 other atoms carbon is at the center of a tetrahedron and the 4 other atoms are located at the corners. This is knownThis is known As a Tetrahedron If there are 3 C’s Bonded to each other Then there are 3 joined tetrahedrons

12 Vocabulary Interlude HydrocarbonsHydrocarbons: organic compounds containing only Carbon and Hydrogen. –Straight chain: All “internal” C bonded to only 2 other C’s Ex: c-c-c-c-c-c-c –Branched: One or more int. C bonded to 3 or 4 other C’s Ex: c-c-c-c-c-c-c-c c | | | c c c-c-c | c

13 Vocabulary SaturatedSaturated: organic compounds containing only single bonds (carbon bonded to 4 atoms) UnsaturatedUnsaturated: organic compounds containing one or more double or triple bonds.

14 Vocabulary Homologous SeriesHomologous Series: a group of compounds with related structures and properties. –Each member of the series differs from the one before it by the same additional unit. (Ex. The Alkanes; each differs by one -CH 2 unit) Ex: CH 4 C 2 H 6 C 3 H 8

15 Primary Categories of Hydrocarbons There are 3 major Hydrocarbon Categories –These can be Straight Chain or Branched Alkanes (Single Bonds) [hydrogen = 2n +2] –CH 3 CH 2 CH 2 CH 3 Alkenes (Double Bond) [H = 2n] –CH 3 CH 2 CH=CH 2 Alkynes (Triple Bond) [H = 2n – 2] –CH 3 CH 2 C CH Table Q in your Reference Tables is where you can Get this information!

16 Naming straight-chain Alkanes ane names aneAll alkane names have the suffix –ane. The prefix depends on the number of C’s. Ex:Methane1 Carbon Ethane2 Carbon What’s the Molecular formula of each?

17 Prefix# of C atoms Meth ane1 Eth2 Prop3 But4 Pent5 Hex6 Hept7 Oct8 Non9 Dec10 (Check out Table P in your Reference Tables)

18 Alkanes A Homologous series of saturated hydrocarbons. Compounds with a related structure differing by the same repeating unit (-CH2-) -General formula is C n H 2n+2 (n= no. of carbon atoms) FormulaName CH 4 Methane C2H6C2H6 Ethane C3H8C3H8 Propane C 4 H 10 Butane C 5 H 12 Pentane C 6 H 14 Hexane C 7 H 16 Heptane Problem: What’s the molecular formula for the alkane with 27 carbon

19 Problem: What is the structural formula for pentane? Problem: What is the name of the following Hydrocarbon? C-C-C-C-C (Shown w/o the Hydrogens) CH 3 -CH 2 -CH 2 CH 2 -CH 2 -CH 3 Hexane! Is it a branched or straight chain hydrocarbon?

20 Properties of Alkanes Physical Properties Change systematically with the number of C’s As the number of C’s In a homologous series increases, the b.p. & m.p. increases. Mol. Formula M.P.B.P. CH C2H6C2H C3H8C3H C 4 H C 5 H C 6 H C 7 H C 8 H C 9 H (Due to increasing Intermolecular force in the form of temporary dipoles)

21 SIMPLE HYDROCARBONS Draw the structural formula, condensed structural formula and molecular formula for the following: –p–propane –O–Octane Which should have the highest M.P & B.P.?