Topic: Saturated hydrocarbons – alkanes

Target group

Elementary school student (grades 7. and 8.)

Core curriculum:

Elementary school. Chemistry.

IX. Compounds of carbon with hydrogen – hydrocarbons. Pupil:

1 . defines the terms: saturated hydrocarbons (alkanes) and unsaturated hydrocarbons (alkenes, alkynes);

2 . creates a general formula of the homologous series of alkanes (based on the formulas of successive alkanes) and records the total formula of an alkane with a given number of carbon atoms; draws structural and semi‑structural (group) patterns of alkanes with straight‑to‑five carbon atoms in the molecule; gives their systematic names.

General aim of education

The student creates a series of saturated hydrocarbons

Key competences

• communication in foreign languages;

• digital competence;

• learning to learn.

Criteria for success
The student will learn:

• define terms of saturated alkanes and saturated hydrocarbons

• create a general formula of the homologous series of alkanes;

• record the total formula of any alkane with a given number of carbon atoms in the molecule;

• record structural and semi‑structural formulas of alkanes.

Methods/techniques

• expository

  • talk.

• activating

  • discussion;

  • snowball method.

• 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.

Realization

1. In order to remind you of the previous lesson, the teacher asks the students to explain the concept of hydrocarbons. He asks for the location of carbon in the periodic table of elements, allowing the use of textbooks or an array in a chemical laboratory. By directing the conversation, he aims to indicate to the students that the carbon atom has four electrons on the last shell. Referring to this statement, he informs that in organic compounds coal always accepts valence IV. He talks briefly about the properties of methane.

2. The teacher explains the principles of naming alkanes, gives their systematic names (obligatory to five atoms of carbon in a molecule, but can give eg to dekan).

3. The lecturer displays on the multimedia board the presentation „Total, structural and semi‑structural formulas (including semi‑structural group) of alkanes up to five carbon atoms per molecule”. Then he asks the pupils to define the concept of a homologous series of alkanes based on the whole scheme of creating a homologous series of alkanes.

4. The students consolidate the acquired information, discussing it with their nearest neighbors („tell your neighbor” method).

5. The teacher divides the students into groups. Then he distributes ball‑and‑ball models and asks you to build model formulas for the first five alkanes. Then he checks the correctness of the task.

6. The teacher informs students that their task will be to determine the definition of isomers. Students use the available information sources and work using the snowball method. First, in pairs, they prepare a definition, the next combine into fours, verify their proposals and set a common definition. In the next steps, they merge into more numerous groups and together form the content of the definition until the general class variant is established. The teacher watches over the correctness of the task.

7. Students, working individually or in pairs, carry out interactive exercises to check and consolidate knowledge learned during the lesson. Selected people discuss the correct solutions for interactive exercises. The teacher completes or straightens the statements of the proteges.

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

Saturated hydrocarbons – alkanes

Methane, whose molecules are composed of one carbon atom and hydrogen atoms, is the simplest hydrocarbon. The place of carbon in the periodic table indicates that it has four valence electrons. In organic compounds carbon is always four‑valent (IV) – it can form up to four chemical bonds. The carbon atom, combined with four hydrogen atoms, forms a compound with the formula , i.e. methane. What do we already know about it? Expand the table and find out.

Natural gas components, apart from methane, are other alkanes: ethane, propane, butane. Their names are common. Starting with the pentane, the names are made up of Greek numerals: penta- (five), hexa- (six) etc., denoting the number of carbon atoms in the molecule, by the addition of suffix -ane.

Alkanes are saturated hydrocarbons whose molecules have only single bonds between carbon atoms.

All the alkane molecules in the homologous series have single bonds (which means that the maximum number of hydrogen or carbon atoms is attached to each carbon atom), hence the name saturated hydrocarbons.

Isomers

Alkanes or other organic compounds of the same molecular formula may differ in structure – such compounds are called isomers. There are compounds with a „straight” chain, in which all carbon atoms are bonded to no more than two other carbon atoms, and compounds with a „branched” chain, in which at least one carbon atom is bonded to more than two other carbon atoms.

The more carbon atoms in the alkane molecule, the more possibilities of bonding between them. If all carbon atoms in the alkane molecule are arranged in one line and there are no branches, the name of the molecule can be given with the letter n- at the beginning (abbreviation from normal).
Butane with the molecular formula CIndeks dolny 4₄HIndeks dolny 10₁₀ may form a chemical compound with a straight chain (n‑butane) or a branched chain (isobutane).

• In organic compounds carbon is always of four‑valent.

• Saturated hydrocarbons (alkanes) are saturated hydrocarbons whose molecules have only single bonds between carbon atoms.

• Saturated hydrocarbons form the homologous series with the following generalized formula CIndeks dolny n_nHIndeks dolny 2n+2_2n+2.