Alkanes

Alkanes

What is it?

Alkanes are saturated hydrocarbons: only C-C and C-H single bonds. General formula CnH2n+2 (open chain). Unreactive towards many reagents; they burn. Homologous series: each extra CH2 raises b.p. (larger London forces). Straight vs branched: branched often slightly lower b.p. Meaning: fuels and starting points, not a long reaction menu. Methane to butane are gases at room T (school). Saturated C-C single bonds; general CnH2n+2; unreactive — combustion and free-radical halogenation main. Show curly arrows on addition mechanisms; Markovnikov reasoning must precede the product structure.

In simple words

• Alkanes are saturated hydrocarbons: only C-C and C-H single bonds.
• 1. STRUCTURE: Tetrahedral carbons.
• 2. REACTIONS: Combustion: CO2 + H2O if complete; CO / C if not (air chapter).
• Exam reminder: Exam alkane: saturated, CnH2n+2 main reaction: combustion Cl2 / UV substitution named, not a factory

Important terms

ALKANES: Alkanes are saturated hydrocarbons: only C-C and C-H single bonds.

1. STRUCTURE: Tetrahedral carbons.

2. REACTIONS: Combustion: CO2 + H2O if complete; CO / C if not (air chapter).

What you should learn

• Explain alkanes in simple chemical language.
• Connect 1. structure with 2. reactions using equations, observations, or trends where needed.
• Answer a short Federal Board question with the correct terms and a clear reason.

Examples

• CH4 methane
• C4H10 two isomers
• b.p. up with size

STRUCTURE

Tetrahedral carbons. Free rotation about C-C. Isomers from C4. Cycloalkanes CnH2n (named if asked). Crude oil fractions later (energy chapter). C1-C4 gases, C5-C17 liquids, higher solids — physical trend for homologous series.

REACTIONS

Combustion: CO2 + H2O if complete; CO / C if not (air chapter). Substitution with Cl2 in UV (free radical named): CH4 + Cl2 -> CH3Cl + HCl as a type, not a chlorination plant. Cracking named in energy. Source: crude oil fraction; cracking makes shorter alkanes and alkenes.

Full school-level explanation

Alkanes are saturated hydrocarbons: only C-C and C-H single bonds. General formula CnH2n+2 (open chain). Unreactive towards many reagents; they burn. Homologous series: each extra CH2 raises b.p. (larger London forces). Straight vs branched: branched often slightly lower b.p. Meaning: fuels and starting points, not a long reaction menu. Methane to butane are gases at room T (school). Saturated C-C single bonds; general CnH2n+2; unreactive — combustion and free-radical halogenation main. Show curly arrows on addition mechanisms; Markovnikov reasoning must precede the product structure.

Structure, then what they do:

WHAT — ALKANES

Alkanes are saturated hydrocarbons: only C-C and C-H single bonds. General formula CnH2n+2 (open chain). Unreactive towards many reagents; they burn. Homologous series: each extra CH2 raises b.p. (larger London forces). Straight vs branched: branched often slightly lower b.p. Meaning: fuels and starting points, not a long reaction menu. Methane to butane are gases at room T (school). Saturated C-C single bonds; general CnH2n+2; unreactive — combustion and free-radical halogenation main. Show curly arrows on addition mechanisms; Markovnikov reasoning must precede the product structure.

WHY — Why this topic matters

ALKANES is an independent FBISE learning unit because students must use its definitions, conditions, equations, or trends separately in explanations and calculations.

HOW — How it works

STRUCTURE: Tetrahedral carbons. Free rotation about C-C. Isomers from C4. Cycloalkanes CnH2n (named if asked). Crude oil fractions later (energy chapter). C1-C4 gases, C5-C17 liquids, higher solids — physical trend for homologous series. Examples: CH4 methane; C4H10 two isomers; b.p. up with size. REACTIONS: Combustion: CO2 + H2O if complete; CO / C if not (air chapter). Substitution with Cl2 in UV (free radical named): CH4 + Cl2 -> CH3Cl + HCl as a type, not a chlorination plant. Cracking named in energy. Source: crude oil fraction; cracking makes shorter alkanes and alkenes. Examples: Blue flame complete; UV / Cl2 named; No other easy addition. Exam alkane: saturated, CnH2n+2 main reaction: combustion Cl2 / UV substitution named, not a factory

STRUCTURE

Tetrahedral carbons. Free rotation about C-C. Isomers from C4. Cycloalkanes CnH2n (named if asked). Crude oil fractions later (energy chapter). C1-C4 gases, C5-C17 liquids, higher solids — physical trend for homologous series.

Remember

• four bonds, no C=C

Examples

• CH4 methane
• C4H10 two isomers
• b.p. up with size

REACTIONS

Combustion: CO2 + H2O if complete; CO / C if not (air chapter). Substitution with Cl2 in UV (free radical named): CH4 + Cl2 -> CH3Cl + HCl as a type, not a chlorination plant. Cracking named in energy. Source: crude oil fraction; cracking makes shorter alkanes and alkenes.

Remember

• combustion + named sub

Examples

• Blue flame complete
• UV / Cl2 named
• No other easy addition

Remember

• saturated = single bonds
• burn, few other reactions
• burn + named sub
• school only
• four bonds, no C=C
• combustion + named sub
• saturated = single bonds
• burn, few other reactions

How the ideas connect

Exam alkane: saturated, CnH2n+2 main reaction: combustion Cl2 / UV substitution named, not a factory

Deeper understanding

Go beyond memorising Alkanes. Connect the definition to reasons, relationships, exceptions, and exam wording.

How the ideas connect

Exam alkane: saturated, CnH2n+2 main reaction: combustion Cl2 / UV substitution named, not a factory

Common mistakes

Exam focus

Core Idea

1. STRUCTURE

2. REACTIONS

Exam Example

Exam focus

Quick revision

• saturated = single bonds
• burn, few other reactions
• burn + named sub
• school only
• ALKANES: Alkanes are saturated hydrocarbons: only C-C and C-H single bonds.
• 1. STRUCTURE: Tetrahedral carbons.

Fuel chemistry. No chlorination-plant or weapon use.

For long answers on Alkanes: define clearly → explain the main parts → give one example → state one exam caution.