ChemistryChapter 16: Hydrocarbons
Alkanes
Alkanes are saturated hydrocarbons: only C-C and C-H single bonds.
Learning objectives
- 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.
Definition
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.
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).
Relationship
- saturated = single bonds
Overview
Structure, then what they do:
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
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
In simple words
Fuel chemistry. No chlorination-plant or weapon use.
Key points
- saturated = single bonds
- burn, few other reactions
- four bonds, no C=C
- combustion + named sub
Exam preparation
Exam Focus
Quick revision
Revision Zone
Review the key facts, formulas and checks before you move on.Alkanes
Sticky Notes · Quick Revision
Core Idea
- 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.
1. 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.
- CH4 methane
- C4H10 two isomers
- b.p. up with size
2. 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.
- Blue flame complete
- UV / Cl2 named
- No other easy addition
Exam Example
- Exam alkane:
- saturated, CnH2n+2
- main reaction: combustion
- Cl2 / UV substitution named, not a factory
Common Misconceptions
- Do not confuse 1. STRUCTURE with 2. REACTIONS; state the difference before giving an example.
- Writing only “saturated = single bonds” is not enough. Explain what it means in a complete sentence.
FBISE Exam Check
- Explain alkanes, compare its two main parts, and include the correct chemical evidence.
- Fuel chemistry. No chlorination-plant or weapon use.
60-second revision
- 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
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