Hydrocarbons For 9th And 10th

Key ConceptsThis chapter covers what hydrocarbons are, how to distinguish alkanes, alkenes, and alkynes, and how to use IUPAC-style naming rules for simple carbon chains. You need these ideas because exam questions often test both functional group recognition and correct chain naming.

You MUST know:

Hydrocarbons contain only carbon (C) and hydrogen (H) atoms.

Alkanes have only single bonds between carbon atoms (general formula: CnH2n+2).

Alkenes have at least one C=C double bond (general formula: CnH2n).

Alkynes have at least one C≡C triple bond (general formula: CnH2n-2).

To name a simple chain, use IUPAC steps:

Find the longest continuous carbon chain.

Count the chain length (n carbons) → choose the base name: meth-, eth-, prop-, but-, pent-, hex-...

Number the chain from the end giving the lowest possible number to the bond position (for double/triple bonds).

For unsaturated chains, include the -ene or -yne ending and the bond position (e.g., but-2-ene).

Exam quick check:

Single → alkane; double → alkene; triple → alkyne.

Double/triple bond position comes from numbering the chain correctly.

Before you continue: Can you state the difference in bonding and formula between an alkane and an alkene?

Key TermsHydrocarbon - a compound made of only carbon and hydrogen atoms.

Alkane - hydrocarbon with only C-C single bonds; general formula CnH2n+2.

Alkene - hydrocarbon with at least one C=C double bond; general formula CnH2n.

Alkyne - hydrocarbon with at least one C≡C triple bond; general formula CnH2n-2.

Longest carbon chain - the continuous sequence of carbon atoms used as the parent for naming.

IUPAC naming (parent chain + numbering) - rules for choosing the parent chain and numbering to give the lowest bond position.

Bond position number - the number showing where the C=C or C≡C occurs in the numbered chain.

Active RecallHydrocarbon = __________

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Alkane = __________

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Alkene = __________

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Alkyne = __________

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Longest carbon chain = __________

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IUPAC naming (parent chain + numbering) = __________

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Bond position number = __________

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Worked ExamplesExample 1: Identify the type from bondingGiven: A chain with one C=C double bond and no triple bonds.

Look for bond types between carbon atoms.

A C=C means it is an alkene (ending will be -ene).

If there is only one double bond and no triple bonds, name will be based on the longest chain and the double-bond position.

Now you try: A hydrocarbon has a C≡C triple bond and no double bonds. What type is it?

__________

__________

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Example 2: Name a simple alkane from a diagram (straight chain)Given: A straight chain of 5 carbon atoms with only single bonds.

Find the longest carbon chain: 5 carbons → base name pent-.

Only single bonds → alkane → ending -ane.

No bond position needed because there are no double/triple bonds.

Name = pentane.

Now you try: A straight chain of 3 carbon atoms with only single bonds. Name it.

__________

__________

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Example 3: Name an alkene using correct numberingGiven: A 6-carbon chain with a double bond between carbon 2 and 3 (from the left end).

Longest chain length = 6 → base name hex-.

Double bond → -ene.

Bond position = 2 (written as but/hex/etc.-2-ene style).

Name = hex-2-ene.

If the double bond were also “2” from the other end, numbering choice would not change; if different, choose the lowest number.

Now you try: A 4-carbon chain has a double bond between carbon 1 and 2 (as drawn from one end). What is the correct name?

__________

__________

__________

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Practice Questions1) (Easy) ClassificationState whether each is an alkane, alkene, or alkyne based on the carbon-carbon bonds.

a) Only single bonds

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