Lesson Notes By Weeks and Term - Senior Secondary 1

Carbon and its compounds: Alkanes

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Term: 3rd Term

Week: 6

Class: Senior Secondary School 1

Age: 15 years

Duration: 40 minutes of 5 periods each

Date:       

Subject:      Chemistry

Topic:-       CARBON AND ITS COMPOUNDS: Alkanes

SPECIFIC OBJECTIVES: At the end of the lesson, pupils should be able to

  1. Highlight the properties of alkanes
  2. Discuss the structure, preparation and uses of alkanes

INSTRUCTIONAL TECHNIQUES: Identification, explanation, questions and answers, demonstration, videos from source

INSTRUCTIONAL MATERIALS: Videos, loud speaker, textbook, pictures

INSTRUCTIONAL PROCEDURES

PERIOD 1-2

PRESENTATION

TEACHER’S ACTIVITY

STUDENT’S ACTIVITY

STEP 1

INTRODUCTION

The teacher reviews the previous lesson on hydrocarbons

Students pay attention

STEP 2

EXPLANATION

He highlights the properties of alkanes

 

Students pay attention and participates

STEP 3

DEMONSTRATION

He discusses the structures, preparation and uses of alkanes

Students pay attention and participate

STEP 4

NOTE TAKING

The teacher writes a summarized note on the board

The students copy the note in their books

 

NOTE

CARBON AND ITS COMPOUNDS

Alkanes

WHAT ARE ALKANES?

  1. Usually used as fuels. examples: natural gas, petrol, diesel
  2. They are homologous series with a general formula of CnH2n+2. Where n is the number of carbon

atom. Example: propane has three carbon atom, thus n=3. Then the formula of propane is C3H8

  1. Their names end with a suffix – ane
  2. Each member differs from the next by –CH2 Eg: methane: CH4, ethane: C2H6

Structure of Alkanes

shows how all atoms in a molecule joined together by drawing lines between atoms to represent the bonds. Example: butane has a formula of C4H10, therefore the structural formula is:

It has 4 carbon atoms bonded together with 10 hydrogen atoms. Organic compound containing only single bond is saturated. Eg: methane

All alkanes are saturated.

 

Physical Properties of Alkanes

  1. Melting points and boiling points increase as the bonds become larger and heavier which increases the forces of attraction between molecules so more energy (from heat) is needed to separate them with the increase of strength of forces of attraction.
  2. Alkanes are Insoluble in water but soluble in organic solvents such as tetra chloromethane as alkanes are organic compounds.
  3. Alkane density increases down the series; all alkanes are less than 1g/cm3
  4. Alkanes become more Viscous going down the series as the longer molecules tangles together when it flows.
  1. Alkanes become less flammable down the series as Boiling point becomes larger.
  2. Alkanes are unreactive with metals, water, acids or bases because the C –C and C –H covalent bonds are harder to break

 

Chemical properties of alkanes

  1. Combustion Alkanes burn in air to always form carbon dioxide and water.

C2H6(g)  + O2(g)àCO2(g) + H2O(g)

  1. When there is insufficient oxygen, the product is ALWAYS carbon monoxide and unburnt carbon.

2C4H10 (g) + 13O2(g) 8CO2(g) +10 H2O (l)

Higher alkanes burn less completely and give soot (unburnt carbon) and CO

 

Reaction with Chlorine/Other Halogens (Alkyl Halides)

Chlorine molecule replaces the hydrogen atom in the alkane with chlorine atom

Substitution reaction the reaction in which one or more atoms replaces other atoms in a molecule. Light is needed to break covalent bond between chlorine molecule atoms

 

EVALUATION:    1. What are alkanes?

  1. Describe the structure of alkanes
  2. Highlight two physical and chemical properties of alkanes
  3. How can alkanes be prepared?
  4. State two uses of alkanes

CLASSWORK: As in evaluation

CONCLUSION: The teacher commends the students positively