Lesson 1: Functional Groups | CHE 2.5

Lesson at a Glance | He Tirohanga Whakamua

Do NowWhy carbon forms millions of unique molecules10 min

Homologous SeriesDefinition & general formula trends15 min

7 Functional GroupsAlkane, Alkene, Alkyne, Haloalkane, Alcohol, Acid, Amine15 min

Portfolio EntryWrite Section 1: Homologous Series & Functional Group Map10 min

Exit CheckIdentify functional group from 3 structural formulas5 min

Ngā Whāinga Ako | Learning Intentions

Students will know

That carbon is tetravalent (always forms 4 covalent bonds) enabling stable single, double, and triple bonds in chains and rings.
The definition of a homologous series (family of organic compounds with the same functional group, same general formula, and similar chemical properties).
The 7 key NCEA Level 2 functional groups: Alkanes (single $C - C$ ), Alkenes ( $C = C$ ), Alkynes ( $C \equiv C$ ), Haloalkanes ( $- X$ ), Alcohols ( $- O H$ ), Carboxylic Acids ( $- C O O H$ ), and Amines ( $- N H_{2}$ ).

Students will demonstrate

By completing a structural, condensed, and molecular formula mapping grid across 7 functional groups.
By completing Section 1 of their Level 2 Organic Chemistry Mastery Portfolio.

Curriculum alignment

NZC (2007) · Science · Level 7 · Material World: “Relate properties of matter to structure and bonding.”

Do Now | Tīmatanga Whakaaro (10 min)

Tetravalent Carbon Prompt:

"Silicon has 4 valence electrons just like carbon. Why did life on Earth evolve using carbon backbones instead of silicon backbones?"

Unpack: Carbon carbon bonds ( $C - C$ ) are exceptionally strong and stable in water. Carbon's small atomic radius allows it to form stable double ( $C = C$ ) and triple ( $C \equiv C$ ) bonds, creating infinite functional structural variety.

7 NCEA Level 2 Organic Families (15 min)

Family Name	Functional Group	General Formula	Example (3-Carbon)
Alkane	$C - C$ single bonds	$C_{n} H_{2 n + 2}$	Propane ( ${CH}_{3} {CH}_{2} {CH}_{3}$ )
Alkene	$C = C$ double bond	$C_{n} H_{2 n}$	Propene ( ${CH}_{3} CH = {CH}_{2}$ )
Alkyne	$C \equiv C$ triple bond	$C_{n} H_{2 n - 2}$	Propyne ( ${CH}_{3} C \equiv CH$ )
Haloalkane	$- X$ ( $- C l, - B r, - I, - F$ )	$C_{n} H_{2 n + 1} X$	1-chloropropane ( ${CH}_{3} {CH}_{2} {CH}_{2} Cl$ )
Alcohol	$- O H$ (hydroxyl)	$C_{n} H_{2 n + 1} O H$	Propan-1-ol ( ${CH}_{3} {CH}_{2} {CH}_{2} OH$ )
Carboxylic Acid	$- C O O H$ (carboxyl)	$C_{n} H_{2 n + 1} C O O H$	Propanoic acid ( ${CH}_{3} {CH}_{2} COOH$ )
Amine	$- N H_{2}$ (amino)	$C_{n} H_{2 n + 1} N H_{2}$	Propan-1-amine ( ${CH}_{3} {CH}_{2} {CH}_{2} {NH}_{2}$ )

Homologous Series (15 min)

Where this usually goes wrong: students memorise seven families as seven unrelated facts. A homologous series is a pattern, and the pattern is what lets you predict a compound you have never met.

What makes a series homologous

Same functional group, same general formula, and each member differs from the last by one $C H_{2}$ . Because the functional group is unchanged, chemical behaviour stays the same down the series — only the physical properties shift.

The general formulae are the useful part

Alkanes $C_{n} H_{2 n + 2}$ , alkenes $C_{n} H_{2 n}$ , alkynes $C_{n} H_{2 n - 2}$ . Each degree of unsaturation removes two hydrogens. Given a molecular formula you can work backwards to how many double or triple bonds it must contain.

Do this now: a compound is $C_{6} H_{12}$ . State two different structural possibilities it could be, and say what extra information would let you decide between them.

📁 Organic Chemistry Portfolio — Section 1: Functional Group Families

Students open their Level 2 Chemistry Portfolio and complete Section 1:

Section 1 Requirements:

1. Homologous Series Matrix: Table of 7 functional groups showing General Formula, Functional Group structure, IUPAC suffix, and 2-carbon example.

2. Formula Representation Comparison: Draw 3 representations for Ethanol: 1) Full Structural Formula → 2) Condensed Structural Formula ( ${CH}_{3} {CH}_{2} OH$ ) → 3) Molecular Formula ( $C_{2} H_{6} O$ ).

3. Excellence Definition: 1 paragraph explaining why condensed structural formulas are mandatory in organic chemistry to prevent ambiguity (e.g. $C_{2} H_{6} O$ represents both Ethanol and Dimethyl ether).

Exit Verification | Ka Mutu Hoki (5 min)

Exit Check:

"My Section 1 correctly identifies all 7 functional group structures and explains why condensed structural formulas prevent isomer confusion."

Teacher Planning & NCEA Alignment

NCEA Level 2 Chemistry Alignment (4 Credits External):

Functional Groups: Identify alkanes, alkenes, alkynes, haloalkanes, alcohols, carboxylic acids, and amines.
Homologous Series: Recognise structural and chemical trends in organic families.

Vocabulary: Organic chemistry, tetravalent carbon, homologous series, functional group, structural formula, condensed structural formula, molecular formula.

Other teaching approach: Guided Viewing & Practical Chemistry →

Lesson 1: Functional Groups & Homologous Series