Unit 6 Chapter 10 Introduction to Organic Chemistry Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings 1

Organic Chemistry Why is it important? >90% of compounds are organic What is an organic compound is a compound made from carbon atoms. has one or more C atoms. has many H atoms. may also contain O, S, N, and halogens. 2

Organic Compounds Typical organic compounds have covalent bonds. have low melting points. have low boiling points. are flammable. are soluble in nonpolar solvents. are not soluble in water. oil (organic) and water (inorganic) 3

Organic vs. Inorganic Propane, C 3 H 8, is an organic compound used as a fuel. NaCl, salt, is an inorganic compound composed of Na + and Cl - ions. 4

Comparing Organic and Inorganic Compounds Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings 5

Learning Check Identify each characteristic as most typical of compounds that are 1) inorganic 2) organic. A. has a high melting point B. is not soluble in water C. has a formula CH 3 ─CH 2 ─CH 3 D. has a formula MgCl 2 E. burns easily in air F. has covalent bonds (some 1) 6

In organic compounds carbon has 4 valence electrons and hydrogen has 1. C H to achieve an octet, C forms four bonds. H H  H  C  H H C H  H H CH 4, methane Writing Formulas for Alkanes 7

Tetrahedral Structure of Carbon A carbon atom with four single, covalent bonds, has a tetrahedral shape. 8

Organic Molecules In organic molecules, valence electrons are shared. covalent bonds form between carbon atoms. C-C bonds are very strong, can form long chains. H H H H H  C  C  HH C C H H H H H ethane, CH 3 ─CH 3 9

Tetrahedral Structure of Carbon In molecules with two or more carbon atoms, each carbon atom with four single bonds has a tetrahedral shape. (Rotation, Maximum space) 10

Alkanes Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings Compounds containing only C and H All bonds are single bonds (2 electrons are shared) 11

Structural Formulas Alkanes are written with structural formulas that are expanded to show each bond (Lewis Structure). condensed to show each carbon atom and hydrogen atoms attached to that carbon. Expanded (Lewis) Condensed H H C H CH 4, methane H 12

Expanded and Condensed Structures 13

Structural Formulas Condensed formulas are written for expanded structural formula by showing each carbon and the attached hydrogen atoms. Expanded Condensed H H H H │ │ │ │ H─C ─C ─C ─C ─ H CH 3 ─CH 2 ─CH 2 ─CH 3 │ │ │ │ H H H H 14

Names of Alkanes The names of alkanes are determined by the IUPAC (International Union of Pure and Applied Chemistry) system. end in –ane. with 1-4 carbons in a chain use prefixes as follows. Name # Carbons Structural Formula Methane1CH 4 Ethane2CH 3 CH 3 Propane3CH 3 CH 2 CH 3 Butane4CH 3 CH 2 CH 2 CH 3 15

Names of Alkanes Alkanes with 5-10 carbon atoms in a chain use Greek prefixes. Name # Carbons Structural Formula Pentane 5 CH 3 CH 2 CH 2 CH 2 CH 3 Hexane 6 CH 3 CH 2 CH 2 CH 2 CH 2 CH 3 Heptane 7 CH 3 CH 2 CH 2 CH 2 CH 2 CH 2 CH 3 Octane 8 CH 3 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 3 Nonane 9 CH 3 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 3 Decane 10 CH 3 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 2 CH 3 Know the 1 st eight alkanes (name and structure) 16

Learning Check A. Write the condensed formula for: H H H H H H C C C C C H H H H H H B.What is its molecular formula? (Gives total # of each atom, does not indicate how they are arranged) C. What is its name? CH 3 ─CH 2 ─CH 2 ─CH 2 ─CH 3 C 5 H 12 pentane 17

Some Structures for Butane 18

Hexane has Six Carbon Atoms Hexane is an alkane with six carbon atoms in a continuous chain. has a “zig-zag” look because each carbon atom is at the center of a tetrahedron. is represented by a ball-and-stick model as shown below. 19

Cycloalkanes are cyclic alkanes. have two hydrogen atoms fewer than the open chain. (remember each carbon has 4 bonds) are named by using the prefix cyclo- before the name of the alkane chain with the same number of carbon atoms. 20

Cycloalkanes The structural formulas of cycloalkanes are usually represented by geometric figures, Cyclopropane CH 2 CH 2 CH 2 Cyclobutane CH 2 CH 2 CH 2 21

More Cycloalkanes Cyclopentane CH 2 CH 2 CH 2 CH 2 Cyclohexane CH 2 22

Properties of Alkanes Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings 23

Some Properties of Alkanes Alkanes are nonpolar. insoluble in water. less dense than water. flammable in air. 24

Some Properties of Alkanes Alkanes with 1-4 carbon atoms are methane, ethane, propane, and butane. gases at room temperature. used as heating fuels. 25

Some Properties of Alkanes Alkanes with 5-8 carbon atoms are liquids at room temperature. pentane, hexane, heptane, and octane. very volatile. used to make gasoline. Alkanes with 9-17 carbon atoms are liquids at room temperature have higher boiling points. are found in kerosene, diesel, and jet fuels. 26

Some Properties of Alkanes Alkanes with 18 or more carbon atoms have high molar masses. are waxy solids at room temperature. used in waxy coatings of fruits and vegetables. 27

Combustion In combustion reactions, alkanes react with oxygen. CO 2, H 2 O and energy are produced. Alkane + O 2 CO 2 + H 2 O + heat 28

Learning Check Write a balanced equation for the complete combustion of propane. 29

Solution Unbalanced equation C 3 H 8 + O 2 CO 2 + H 2 O First: Balance C C 3 H 8 + O 2 3CO 2 + H 2 O Then: Balance H C 3 H 8 + O 2 3CO 2 + 4H 2 O Last: Balance O C 3 H 8 + 5O 2 3CO 2 + 4H 2 O (Balanced) 30