A graphic representation that shows the symbols for each atom in a compound, with straight lines joining them to represent the covalent bonds.
Example: Ethene (C2 H4)
From the molecular formula, we know that ethene has 2 carbon atoms and 4 hydrogen atoms:
Carbon atoms will be joined by a double bond as each carbon atom needs 4 bonds in total
A condensed representation that shows the symbols for each atom in a compound, with straight lines joining them to represent the covalent bonds.
This displayed formula of ethene can be split up into sections and written as a formula:
- Substitution: A reaction where one atom is swapped with another atom
- Example: Methane reacts with bromine under ultraviolet light
Methane + Bromine → Bromomethane + Hydrogen Bromide
CH4 + Br2 → CH3Br + HBr
- Addition: A reaction in which one molecule combines with another 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
Ethene + Bromine → Dibromoethane
C2H4 + Br2 → C2H4Br2
- Combustion: This is the scientific term for burning. In a combustion reaction, a 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
C3H8 + 5O2 → 3CO2 + 4H2O
- This is termed complete combustion
- If there is a limited supply of air / oxygen, the products are carbon monoxide and water:
CH4 + ½O2 → CO + 2H2O
- This is termed incomplete combustion