Lesson Notes By Weeks and Term - Senior Secondary 1

Carbon and its compounds: Alkenes

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Term: 3rd Term

Week: 7

Class: Senior Secondary School 1

Age: 15 years

Duration: 40 minutes of 5 periods each

Date:       

Subject:      Chemistry

Topic:-       CARBON AND ITS COMPOUNDS: Alkenes

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

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

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 alkanes

Students pay attention

STEP 2

EXPLANATION

He highlights the properties of alkenes

 

Students pay attention and participates

STEP 3

DEMONSTRATION

He discusses the structures, preparation and uses of alkenes

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

Alkenes

The alkenes are homologous series of hydrocarbons with a general molecular formula CnH2n. they are sp2 hybridized and unsaturated

 

Structure of Alkenes

Alkene compound containing C = C double bond, it is said to be unsaturated because not all Carbon atoms are bonded to the maximum number of 4 other atoms

 

PHYSICAL PROPERTIES OF ALKENES

  • Colourless gas with a faint sweetish smell.
  • Ethene is completely soluble in organic solvents and slightly soluble in water.
  • It is lighter than air.
  • No action on litmus
  • Boiling point of ethene is -102 ° C and melting point is –169° C.

 

CHEMICAL PROPERTIES OF ALKENES

Reactions of Alkenes

  1. Combustion: alkenes burn in air to form carbon dioxide and water

C2H4 (g) + 3O2 (g)à  2CO2(g) + 2H2O(l)

Incomplete combustion forms soot and CO. This is produced more than in alkane 

  1. Addition Reaction Is the reaction of 2 or more molecules to form a single product.

E.g

       a. Addition of hydrogen: Alkenes react with hydrogen to form alkanes, called

Hydrogenation. Nickel is used as catalyst and then heat.

C2H4 (g) + H2(g)à      C2H6(g

       b. Addition of bromine to ethene for example. Bromine add to C = C double bond of alkene molecules. In the presence of Phosphoric acid (H3PO4), high temperature of 300oC and 60-70 atm. pressure are needed as catalyst .Eg: ethene to 1,2 –dibromoethane

C2H4(g) + Br2(g)à      C2H4Br2(l)

Nomenclature (n)(bromo) + (alkene name), where n is the number of bromine atoms. E.g. Above, Ethene reacts with 2 bromine atoms producing DI(2) BROMO(Bromine) ETHENE(alkene name). Hence we call the product DIBROMOETHANE.-

       c. Addition of water Alkene reacts with water, in the form of steam, to produce alcohol. Alkene + steam is passed over phosphoric acid (H3PO4) catalyst and temperature of 300oC. H2O molecule adds to C = C bonds to form alcohol.

C2H4(g) + H2O(g) à   C2H5OH(l) or CH3CH2OH(l)

Nomenclature

(alkene name) + (-ol) E.g. in above, the alkene ethene (C2H4) reacts with steam to form

ETHANOL(alkene name –ETHAN + OL group of alcohol)-

 

  1. Polymerization The joining of several identical alkene molecules to form a big molecule Eg: Ethene poly(ethene)

 

USES OF ALKENES

  1. To ripen green fruits
  2. An essential ingredient in manufacture of synthetic chemicals such as ethylene glycol, diethyl ether, ethylene oxide and mustard gas
  3. To manufacture polymers like poly ethylene and poly vinyl chloride
  4. It is also useful in the synthesis of important chemicals useful in industries.

EVALUATION:    1. What are alkenes?

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

CLASSWORK: As in evaluation

CONCLUSION: The teacher commends the students positively