Alkanes

Lesson Objectives

• Appreciate the role of hydrocarbons in daily life and the responsibility in using alkane-based products.

• Draw structural formulas for alkanes, specifically from methane to butane.

• Differentiate between hydrocarbons and define alkanes as saturated hydrocarbons, including their general formula, structure, and properties.

Organic Compounds

• Definition: Organic compounds are substances that contain carbon and hydrogen, and may also include elements such as oxygen (O), nitrogen (N), sulfur (S), phosphorus (P), and halogens.

• Historical Perspective: Originally believed to originate solely from living organisms until Friedrich Wöhler synthesized an organic compound from inorganic materials in 1828.

Inorganic Exceptions

• Certain carbon-containing compounds are classified as inorganic, including:

  • Carbon oxides: CO, CO₂

  • Carbonates: CO₃²⁻

  • Carbides

  • Cyanides

Organic and Inorganic Compounds

• Organic Compounds:

  • Primarily involve covalent bonding (electron sharing).

• Inorganic Compounds:

  • Mostly consist of ionic bonding (electron transfer).

Carbon Bonding

• Carbon Characteristics:

  • Carbon has four valence electrons.

  • Forms covalent bonds to complete an octet, achieving a stable arrangement of eight electrons in the outermost shell, similar to noble gases.

• Types of Carbon–Carbon Bonds:

  • Single bonds

  • Double bonds

  • Triple bonds

Hydrocarbons

• Definition: Hydrocarbons are the simplest organic compounds, consisting solely of carbon and hydrogen.

• Types of Hydrocarbons:

  • Saturated Hydrocarbons: Have only single carbon–carbon bonds.

  • Unsaturated Hydrocarbons: Contains double or triple carbon–carbon bonds.

Saturated Hydrocarbons

• Properties:

  • Contain only single bonds between carbon atoms.

  • Generally less reactive and more stable compared to unsaturated hydrocarbons.

• Examples:

  • Methane (gas)

  • Hexane (liquid)

  • Paraffin wax (solid)

Unsaturated Hydrocarbons

• Properties:

  • Contains double or triple bonds between carbon atoms.

  • More reactive than saturated hydrocarbons.

  • Usually exist as gases or liquids at room temperature.

• Examples:

  • Ethene (gas)

  • Ethyne (gas)

  • Vegetable oil (liquid)

Chemical Formulas

• Molecular Formula:

  • Represents the number of atoms in a compound, for instance, C₂H₆.

• Structural Formula:

  • Illustrates the arrangement and bonding of atoms within a molecule.

What Are Alkanes?

• Definition:

  • Alkanes are known as ‘saturated’ hydrocarbons.

  • They are composed solely of hydrogen and carbon, and their molecules consist exclusively of single bonds (C - C).

Keywords

• Alkane: A saturated hydrocarbon that contains only single carbon-carbon bonds.

• Hydrocarbon: A compound containing hydrogen and carbon atoms.

• Homologous Series: A 'family' of organic compounds that share the same functional group and exhibit similar chemical properties.

General Formula for Alkanes

• The general formula for alkanes is given by:
  $C<em>nH</em>{2n+2}$

• Properties of Alkanes:

  • Physical state at room temperature:

  • 1–4 carbons: Gases

  • 5–16 carbons: Liquids

  • 17+ carbons: Solids

  • Chemical Characteristics:

  • Nonpolar and unreactive.

  • Solubility: Dissolve only in nonpolar substances.

Naming Alkanes

• All alkane names end with the suffix -ane.

• The prefix indicates the number of carbon atoms present in the compound.

Prefixes and Corresponding Carbon Numbers

• Meth-: 1 carbon

• Eth-: 2 carbons

• Prop-: 3 carbons

• But-: 4 carbons

• Penta-: 5 carbons

• Hexa-: 6 carbons

• Hepta-: 7 carbons

• Octa-: 8 carbons

• Nona-: 9 carbons

• Deca-: 10 carbons

Basic Naming Rules for Alkanes

1. Identify the longest carbon chain (parent chain).

2. Name branches as alkyl groups (changing –ane to –yl, for example, methyl, ethyl).

3. Number the parent chain starting from the end nearest the branch.

4. Name and number each substituent; utilize di-, tri-, tetra- for multiple occurrences.

5. Use commas between numbers and hyphens between numbers and letters.

6. List substituents in alphabetical order, disregarding the prefixes di-, tri-.

Individual Alkanes in the Homologous Series

Methane

• Methane is the first alkane in the homologous series.

• Characteristics:

  • A greenhouse gas produced by cows and paddy fields.

  • Chemical formula: $CH_4$.

Ethane

• Ethane is the second alkane in the homologous series.

• Characteristics:

  • Used for producing other useful compounds in the petrochemical industry.

  • Chemical formula: C2H6.

Propane

• Propane is the third alkane in the homologous series.

• Characteristics:

  • Utilized for residential cooking and heating systems.

  • Chemical formula: C3H8.

Butane

• Butane is the fourth alkane in the homologous series.

• Characteristics:

  • Primarily used in outdoor cooking and handheld lighters.

  • Chemical formula: C4H10.