Organic Chemistry Introduction IGCSE Chemistry

Introduction to organic chemistry IGCSE

What is organic chemistry?

The scientific study of the structure, properties and reactions of organic compounds. (this does not include carbon dioxide, carbon monoxide or metal carbonates)

What is an organic compound

A chemical compound that contains carbon

Hydrocarbon definition and example

Definition: A compound that only contains hydrogen and carbon

Example: An alkane

How can organic compounds be shown? (5)

• Empirical Formulae

• Molecular Formulae

• General Formulae

• Structural Formulae

Empirical formulae and example

• Shows the simplest possible ratio of the atoms in a molecule

• For example: Hydrogen peroxide is H₂O₂ but the empirical formula is HO

Molecular formula and example

• Shows the actual number of atoms in a molecule

• For example:

General formula and example

• Shows a ratio of atoms in a family of compounds in terms of ‘n’ where n is a varying whole number

• For example, the general formula of a molecule that belongs to the alkane family is C_nH_2n+2

Displayed formula and example

• shows the spatial arrangement of all the atoms and bonds in a molecule - this is also known as the graphical formula.

• For example:

Functional Group

A group of atoms bonded in a specific arrangement that influences the properties of the homologous series

Examples of functional groups (6)

Naming organic molecules

Classifying organic reactions

• Substitution

• Addition

• Combustion

Substitution and example

• A substitution reaction takes place when one functional group is replaced by another

  • Example: Methane reacts with bromine under ultraviolet light

CH₄    +    Br₂       →            CH₃Br   +    HBr

    Methane + Bromine   →   Bromomethane + Hydrogen Bromide

Addition and example

• Takes place when two or more molecules combine to form a larger molecule with no other products

  • Example: Bromine will react with ethene and the bromine molecule will react and add across the double bond of the ethene

C₂H₄     +       Br₂         →         C₂H₄Br₂

Ethene   +   Bromine   →   Dibromoethane

Combustion and example

Combustion

• This is the scientific term for burning. In a combustion reaction, an organic substance reacts with oxygen to form carbon dioxide (or carbon monoxide if incomplete combustion) and water.

  • Example: Alkenes burn when heated in air of oxygen

  • If there is an unlimited supply of air / oxygen, the products are carbon dioxide and water:

CH₄   +   2O₂   →   CO₂   +   2H₂O

Alkane

Are a saturated molecule - enough bonds for

Alkene

Unsaturated molecule - not enough bonds for the carbon and so forms a double bond

How to know if the hydrocarbon is an alkane or an alkene

Alkanes have a single bond and alkenes have a double one

Does crude oil have mainly Alkanes or alkenes

Alkanes

Formula for alkane

CnH₂n+² (fill in N with the humber of carbon atoms to get your formula)

Use the formula for the alkane Ethane - show your working

Ethane has 2 carbon atoms so to fill in the formula:

CnH₂n+² = C(2)H2×2(+2)

= C₂H₈