Topic: Covalent bonds

Target group

Elementary school student (grades 7. and 8.)

Core curriculum

Elementary school. Chemistry.

II. Internal structure of matter. Pupil:

9) describes the function of the electrons of the outer shell in the joining of atoms; uses the concept of electronegativity to determine the type of bonds (covalent, ionic) in given substances; 10) on the example of molecules HIndeks dolny 2₂, ClIndeks dolny 2₂, NIndeks dolny 2₂, COIndeks dolny 2₂, HIndeks dolny 2₂O, HCl, NHIndeks dolny 3₃, CHIndeks dolny 4₄ describes the formation of chemical bonds; writes the summary and structural formulas of these molecules.

General aim of education

The student explains the concept of covalent bonding and writes dotted, electron bar, combined and structural electron formulas of molecules of gaseous elements.

Key competences

• communication in foreign languages;

• digital competence;

• learning to learn.

Criteria for success
The student will learn:

• to describe covalent (atomic) bond;

• to explain what a molecule is;

• to describe the structure of certain molecules.

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. Students read fragments titled „Noble gases” and „Atoms and types of electrons”. Selected people explain what helium‑group gases are and discuss the concept of chemical bond.

2. Students analyze tables presenting electronic formulas of certain atoms and electronic formulas showing covalent bond formed between hydrogen atoms.

3. Students watch the presentation and note the most important information. Volunteers share the effects of their work on the class forum. Then all students with the help of a teacher formulate the definition of a covalent bond and write it on the form in the abstract.

4. Students read fragments titled „What happens when atoms bond with each other?” and „What is the structure of a nitrogen molecule?”. Volunteers explain what structures are called molecules, and then, on the basis of the table, compare the electronic formulas of hydrogen and chlorine molecules with their molecular formula. They write the electronic formula for the nitrogen molecule. The teacher makes sure that the task has been correctly completed and gives feedback.

5. Students carry out an interactive exercise. The teacher and the students discuss the correct solution .

6. The teacher plays the recording of the abstract. Every now and then he stops it, asking the students to tell in their own words what they have just heard.This way, students practice listening comprehension.

Summary

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

2. 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

3. The student indicated by the teacher sums up the lesson, telling what he has learned and what skills he/she has been practicing.

Homework

1. Imagine that you have the opportunity to interview an academic - a specialist in the field of today's lesson. What questions would you like to ask him? Write them down.

The following terms and recordings will be used during this lesson

Terms

Texts and recordings

Covalent bonds

Non‑metallic elements in the 18th group or family of the periodic table – helium‑group gases also known as noble gases – exhibit the lowest activity. Under regular conditions helium‑group gases do not form molecules and only some of them may create chemical compounds that are relatively unstable. It turns out that the electron configuration of atoms of these noble gases is fixed. While bonding with each other, most atoms of chemical elements strive to attain electron configuration of the helium‑group gas which is closest to them in the period table. For example, hydrogen atoms aim at electron configuration of helium and chlorine atoms aim at configuration of argon.

Atoms can bond both with atoms of the same chemical element and with atoms of other chemical elements. The interaction between atoms which makes them bond permanently is called a chemical bond. Valence electrons are involved in bond formation.

Electron dot diagrams are used while describing chemical bond. If there are pairs of electrons present, sometimes they are represented as lines. Such diagrams are known as electron dot diagrams. The table shows discussed electron formulas of certain atoms.

Hydrogen is a chemical element the atoms of which are not free but they are always bonded in pairs using a chemical bond. Hydrogen atoms share 1 electron. It is believed that they share electrons called shared pairs or bonding pairs. Using symbols a bond formed by 2 hydrogen atoms can be represented as $\text{H : H}$. As the electrons are shared each hydrogen atom gains electron configuration (number of electron) of the noble gas closest in the period table. In this case it is the electron configuration of helium (2 electrons).

This bond between two hydrogen atoms formed using a shared pair of electrons is an example of a bond called covalent bond or atomic bond. This binding consists in sharing electrons and forming the so‑called bonding pairs of electrons which are equally shared by both atoms. Such covalent bonds are formed between atoms of the same non‑metallic element.

Structures created when atoms bond with each other using covalent (atomic) bonds are called molecules. Two hydrogen atoms sharing one pair of electrons are called hydrogen molecules and two chlorine atoms bonded form a chlorine molecule.

The structure of each molecule can be described using a formula. A formula consists of symbols of elements the atoms making up a molecule and a number of atoms forming a molecule written after the symbol of the element (in the lower right index). Such formula created in line with these principles is called a molecular formula.

Hydrogen or chlorine are found in elemental state and they occur in form of diatomic molecules as gases. That is why in order to describe these gases using symbols we always use the following formulas: ${\text{Cl}}_{\text{2}}$, ${\text{H}}_{\text{2}}$.

Atoms of non‑metallic elements can share more than 1 pair of electrons.

A nitrogen molecule made up of two atoms of nitrogen is a good example. The nitrogen atom has five valence electrons, and it needs three electrons to achieve a permanent configuration. That is why each atom shares three electrons. What will its electron formula look like?

There are three bonding pairs of electrons between nitrogen atoms. Such bond is called a triple bond. Molecular formula of a nitrogen molecule is as follows: ${\text{N}}_{\text{2}}$.

The triple bond contains a maximum number of bonds that can be formed between atoms. In nature, there are no chemical compounds with more than three bonds.

• Atoms are bonded with each other with a chemical bond.

• When atoms are bonded with a covalent (atomic) bond, they share 1, 2 or a maximally 3 pairs of electrons.

• Each chemical element, if possible, strives to attain electron configuration of the noble gas closest in the periodic table.

• Atoms of non‑metallic elements form covalent bonds.

• Molecules are formed of atoms bonded with a covalent (atomic) bond.

• Atoms of: ${\text{Cl}}_{\text{2}}{\text{, H}}_{\text{2}}{\text{, N}}_{\text{2}}$ form covalent (atomic) bonds and their bonding pairs of electrons are equally shared by both atoms in the molecule.