Topic: Alkene - properties of unsaturated hydrocarbons

Target group

Elementary school student (grades 7. and 8.)

Core curriculum:

Primary school. Chemistry.

VIII. Compounds of carbon with hydrogen – hydrocarbons. Student:

6) on the basis of the observations describes the physical and chemical properties (combustion, bromine incorporation) of ethene and ethyn; searches for and uses information about their uses;

8) designs and conducts experiments to distinguish saturated hydrocarbons from unsaturated hydrocarbons.

General aim of education

The student discusses the properties of alkenes

Key competences

• communication in foreign languages;

• digital competence;

• learning to learn.

Criteria for success
The student will learn:

• which physical properties have alkenes on the example of ethene;

• which chemical properties have alkenes on the example of ethene.

Methods/techniques

• activating

  • discussion.

• expository

  • talk.

• exposing

  • film.

• programmed

  • with computer;

  • with e‑textbook.

• practical

  • exercices concerned.

Forms of work

• individual activity;

• activity in pairs;

• activity in groups;

• collective activity.

Teaching aids

• e‑textbook;

• notebook and crayons/felt‑tip pens;

• interactive whiteboard, tablets/computers.

Lesson plan overview

Introduction

1. The teacher hands out Methodology Guide or green, yellow and red sheets of paper to the students to be used during the work based on a traffic light technique. He presents the aims of the lesson in the student's language on a multimedia presentation and discusses the criteria of success (aims of the lesson and success criteria can be send to students via e‑mail or posted on Facebook, so that students will be able to manage their portfolio).

2. The teacher together with the students determines the topic – based on the previously presented lesson aims – and then writes it on the interactive whiteboard/blackboard. Students write the topic in the notebook.

3. Health and safety – before starting the experiments, students familiarise themselves with the safety data sheets of the substances that will be used during the lesson. The teacher points out the need to be careful when working with them.

Realization

1. The teacher asks students to follow the task 1 from the abstract and to familiarize themselves with the physical properties of the alkenes. Initiates a discussion about these relationships - it should end with the conclusions that students write in the notebooks.

2. The lecturer announces the film „Testing the combustibility of alkenes” in an abstract. Before the screening students are asked to formulate a research question and a hypothesis. The teacher asks pupils to pay attention to what combustion reactions occur during the experiment. After the screening, the students write observations and conclusions. Then the teacher encourages young people to discuss the properties of alkanes.

3. The teacher asks willing students to write on the board the equations of the total combustion reaction and both incomplete combustion reactions. If necessary, complete the information.

4. The teacher displays on the board the equation of addition (ethylene) addition to bromine (abstract) and discusses its mechanism. Explains the principles of creating names of newly formed chemical compounds - reaction products of attachment. Then, it presents and discusses the hydrogenation equation of ethene. He asks those who want to write the equations of attachment reactions on structural formulas and create names of reaction products, eg ethene with chlorine, ethene with hydrogen bromide, ethene with hydrogen chloride. It encourages students to perform reaction models using plasticine.

5. Students consolidate the acquired information on the properties of alkanes, discussing them with their nearest neighbors („tell your neighbor” method).

6. The teacher asks students (individual work) to perform selected tasks and interactive exercises in an abstract.

Summary

1. The teacher asks the students to finish the following sentences:

   • Today I learned ...

   • I understood that …

   • It surprised me …

   • I found out ...

   The teacher can use the interactive whiteboard in the abstract or instruct students to work with it

Homework

1. Listen to the abstract recording at home. Pay attention to pronunciation, accent and intonation. Learn to pronounce the words learned during the lesson.

2. Make at home a note from the lesson using the sketchnoting method.

The following terms and recordings will be used during this lesson

Terms

Texts and recordings

Alkene - properties of unsaturated hydrocarbons

The reaction of ethene with bromine in anhydrous conditions proceeds according to the equation:

CIndeks dolny 2₂HIndeks dolny 4₄ + BrIndeks dolny 2₂ → CIndeks dolny 2₂HIndeks dolny 4₄BrIndeks dolny 2₂

As a result of this reaction, the multiple bond breaks and a saturated compound dibromoethane forms (the di - prefix informs that there are two bromine atoms in the molecule). This type of reaction is called the addition reaction.

Under appropriate conditions, hydrogen may be added to alkenes. This reaction is called the hydrogenation reaction.

The reaction of ethylene with hydrogen proceeds according to the equation:

CIndeks dolny 2₂HIndeks dolny 4₄ + HIndeks dolny 2₂ → CIndeks dolny 2₂HIndeks dolny 6₆

In 1869, the Russian chemist Vladimir Markownikov proposed a rule defining the direction of the reaction of addition of elements to the double bond between carbon atoms.This principle is that, generally, in addition reactions to the -C=C- bond, occurring in many organic compounds (e.g., alkenes), lower electronegativity atoms or groups attach to it from two carbon atoms to which it was previously attached more atoms or groups with electropositive properties.

The rule is not always satisfied for all addition reactions to the -C=C- bond. Strictly speaking, it is fulfilled only when this reaction occurs through the ionic mechanism, monomolecular. When this reaction proceeds according to another mechanism, it often joins contrary to the Markownikov's rule.

• The physical properties of alkenes and alkynes are similar to the physical properties of the alkanes. They change as the number of carbon atoms in the chain increases.

• Alkenes and alkynes are chemically reactive, flammable, and undergo addition reactions.

• Alkynes are more reactive than alkenes.