CBSE Class 11 · Chemistry
Hydrocarbons
Official NCERT chapter from Chemistry Part I–II (book code kech1). ExamMaster notes are original teaching at CBSE Class 11 depth.
This lesson follows the official chapter “Hydrocarbons” in Chemistry Part I–II. The words below are ExamMaster’s teaching, not a paste from the book. Use the NCERT chapter for the classroom sequence; use these notes to hold the idea without copying exercises or figures.
- CBSE Class 11
- Medium level
- 8 concepts
1Classification
Classification: alkanes (single), alkenes (C=C), alkynes (C≡C), aromatics (benzene-family) as taught. A class is a bond-look, not a smell. Saturated versus unsaturated is the single-versus-multiple split.
Calling every chain “alkane” because it is a fuel-word is a steal.
Figure. Split first by open chain versus cyclic, then by the C–C bond that names the family.
How it works
- Look for C–C only, C=C, C≡C, or a benzene ringThe classify.
- Name alkane / alkene / alkyne / aromaticThe class.
- Keep saturated as all-singlesThe extra word.
2Alkanes
Alkanes: CnH2n+2 (open, unbranched as taught), names methane, ethane, propane…. Substitution (halogen as taught) is the reaction-kind. An alkane is a single-bond chain, not “any petrol”. Conformations if the lesson named eclipse/stagger.
C2H4 as an alkane is a miss — that is the alkene count.
Figure. Each extra CH₂ adds two hydrogens. The school count is CₙH₂ₙ₊₂.
How it works
- Write CnH2n+2 or a named alkaneThe family.
- Name substitution as the school reactionThe chemistry.
- Keep a ring-alkane as a separate count if taughtHonest.
3Alkenes
Alkenes: C=C, CnH2n for one double (open). Addition is the reaction-kind (H2, Br2 as taught). Geometrical cis/trans if the lesson used it. An alkene is the double-bond family, not a brand.
Adding Br2 and still calling it “unchanged alkane” is a miss.
Figure. Same three carbons. The C=C family is short two hydrogens: CₙH₂ₙ.
How it works
- Spot C=CThe alkene.
- Name addition as the school reactionThe chemistry.
- Keep cis/trans only if two different bits sit on the doubleStereo as taught.
4Alkynes
Alkynes: C≡C, CnH2n−2 for one triple (open). Addition can run twice as taught. Ethyne (acetylene) is the school case. An alkyne is the triple-bond family, not a louder alkene.
C2H2 as an alkane because “2 and 2” looks neat is a miss.
Figure. A C≡C at this class is short four hydrogens versus the alkane: CₙH₂ₙ₋₂.
How it works
- Spot C≡CThe alkyne.
- Name addition (possibly two stages)The chemistry.
- Keep ethyne as the first nameThe case.
5Aromatic Hydrocarbon
Aromatic (school): benzene’s ring and the special stability as framed. Substitution (nitration as taught) is the benzene-reaction, not a simple alkene-addition. Aromatic is a ring-family, not “smells nice”.
Treating benzene as three ordinary alkenes ready to add six Br2 is the leftover the lesson warned about.
Figure. Six carbons. Benzene is far short of the open-chain H count. The ring itself is not drawn here.
How it works
- Name the benzene ringAromatic.
- Prefer substitution as the school reactionThe chemistry.
- Keep “smells nice” out of the testA ring-word.
6Carcinogenicity and Toxicity
Carcinogenicity and toxicity (school): some aromatics and taught hydrocarbons are named as harmful; handle as a caution-sentence, not a scare-poster and not a how-to. One named caution is enough. The heading is a safety-claim at this class.
A skull-sticker with no named family is a mute scare.
Figure. Fused-ring count is the school caution flag. This is not a dose table.
How it works
- Name the taught caution (some aromatics, …)The claim.
- Keep it a school safety-sentenceNot a dump.
- Refuse a how-to or a scare-adHonest.
7A definition is a test you can run
Hydrocarbon-word is a test: alkane / alkene / alkyne / aromatic, or the matching formula-count. If you only say “fuel”, you have a heading.
A petrol-pump is not the test.
Figure. A family name is a test you can run on the bonds, then on the H count.
How it works
- Name the bond-look or the CnH… countThe object.
- Give the school sentenceThe test.
- Then the word has contentThe definition ran.
8Name the given before the unknown
The given is a formula or a bond-look. The unknown is the class or the reaction-kind. Copy C2H4 before you treat it as ethane.
Using CnH2n+2 on an alkene is a silent count-swap.
Figure. Name the given chain and the bond locant before you write the suffix.
How it works
- Copy the formula or the C=C / C≡C / ringThe given.
- Name the class or the addition/substitutionThe unknown.
- Then classifyGiven first.
C2H4 is
- An alkene — one double, CnH2n
- An alkane
- Benzene
Count and bond-look.
Notes
- Mapped to the official NCERT chapter “Hydrocarbons”. Original teaching only — no textbook sentences.
- Science here is Physics, Chemistry and Biology ideas at this class, never a language or social-science chapter.
Formulas
- alkane (open): CnH2n+2
- alkene (one C=C, open): CnH2n
- alkyne (one C≡C, open): CnH2n−2
Recap
Hold these pegs from the official chapter “Hydrocarbons”. The wording is ExamMaster’s teaching, not a textbook recap.
- Classification
- Classification: alkanes (single), alkenes (C=C), alkynes (C≡C), aromatics (benzene-family) as taught.
- Alkanes
- Alkanes: CnH2n+2 (open, unbranched as taught), names methane, ethane, propane….
- Alkenes
- Alkenes: C=C, CnH2n for one double (open).
- Alkynes
- Alkynes: C≡C, CnH2n−2 for one triple (open).
- Aromatic Hydrocarbon
- Aromatic (school): benzene’s ring and the special stability as framed.
- Carcinogenicity and Toxicity
- Carcinogenicity and toxicity (school): some aromatics and taught hydrocarbons are named as harmful; handle as a caution-sentence, not a scare-poster and not a how-to.
Practise Hydrocarbons
Reading is free and needs no account. Practice, mocks and progress live in the app.
- A 4-question practice set that ends the chapter
- 1 quick check with worked explanations
- Timed mocks scored with the real marking scheme
- Readiness tracked per topic, kept on your device