1.9.1Unit 1. Structure, Bonding and Introduction to Organic Chemistry
Alkanes – Introduction — IAL Edexcel Linear (Chemistry) Revision Notes & Topical Questions
5 min read 5 parts Lesson 31 of 36 Unit quiz
Curriculum Equation Key معادلة تفاعل تكوين الإستر (الأسترة) - Esterification Reaction EquationFast Exam Solution
R-COOH + R2-OH ⇌ (conc. H₂SO₄) R-COO-R2 + H₂O
Word Equation & Conditions: حمض كربوكسيلي + كحول (في وجود حمض الكبريتيك المركز كعامل حفاز ونازع للماء) ⇌ إستر + ماء
Location & Specifications: الكيمياء العضوية للثانوية العامة والتحصيلي و Edexcel Chemistry.
Section 1 of 5Structure and Naming
Alkanes are the simplest family of organic compounds and are the main components of crude oil.
General formula
- General formula Alkanes are saturated hydrocarbons with the general formula CₙH₂ₙ₊₂ and contain only single bonds.
First members
- First members Methane CH₄, ethane C₂H₆, propane C₃H₈, butane C₄H₁₀, pentane C₅H₁₂ and hexane C₆H₁₄ have one to six carbons.
Aliphatic
- Aliphatic Alkanes are aliphatic because their carbon atoms are joined in chains or non-aromatic rings.
Shape
- Shape Each carbon has four bonding pairs and is tetrahedral, with a bond angle of 109.5°.
Section 2 of 5Physical Properties
Physical Properties
Boiling points
- Boiling points These rise with chain length: methane −162 °C, ethane −89 °C, propane −42 °C, butane −0.5 °C, pentane 36 °C and hexane 69 °C.
Reason
- Reason Longer molecules have more electrons and more surface contact, so the London forces between molecules are stronger.
Branching
- Branching For the same number of carbons, branched alkanes have lower boiling points than straight-chain ones.
Solubility
- Solubility Alkanes are non-polar, so they do not dissolve in water but mix well with other non-polar liquids.
States
- States At room temperature the first four are gases, the middle members are liquids and the large ones are waxy solids.
| Alkane | Formula | Boiling point / °C |
|---|---|---|
| Methane | CH₄ | −162 |
| Propane | C₃H₈ | −42 |
| Pentane | C₅H₁₂ | 36 |
| Hexane | C₆H₁₄ | 69 |
Section 3 of 5Why Alkanes Are Unreactive
1
The C–C and C–H bonds are strong, so a lot of energy is needed to break them.
2
The bonds are non-polar, because carbon and hydrogen have very similar electronegativities.
3
There are no regions of high electron density or partial charges for polar reagents to attack.
4
Alkanes therefore do not react with acids, alkalis or oxidising agents at room temperature.
5
They do react in combustion and in free radical substitution with halogens in sunlight.
Section 4 of 5Using Alkanes
Using Alkanes
Fuels
- Fuels Alkanes burn exothermically, which makes them the main fuels for heating, transport and electricity generation.
Raw materials
- Raw materials Crude oil fractions provide feedstocks for the chemical industry, including the manufacture of plastics.
Solvents
- Solvents Some liquid alkanes dissolve non-polar substances such as grease and oils.
Environmental
- Environmental Burning them releases carbon dioxide, so their use contributes to climate change.
Section 5 of 5Exam Checklist & Tips
1.9.1 – Key Points for the Exam
- Alkane A saturated hydrocarbon with the general formula CₙH₂ₙ₊₂.
- Saturated Containing only single bonds between carbon atoms.
- Hydrocarbon A compound that contains only carbon and hydrogen.
- London forces Weak intermolecular forces that rise with the number of electrons.
- Non-polar Having no permanent separation of charge in the bonds or molecule.
Common Mistakes
- Claiming alkanes are unreactive because their bonds are weak.
- Explaining the rise in boiling point by stronger covalent bonds rather than stronger London forces.
- Stating that alkanes dissolve in water because they are small molecules.
- Giving the general formula as CₙH₂ₙ.
Last updated:
\n