Topic: Polar 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 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 polarized covalent bonding and writes dotted, electron bar, combined and structural electron formulas of molecules of chemical compounds.

Key competences

• communication in foreign languages;

• digital competence;

• learning to learn.

Criteria for success
The student will learn:

• to describe a covalent (atomic) bond;

• to describe a polar covalent bond.

Methods/techniques

• 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.

Realization

1. The students, working in pairs, search the Internet for the information on bonds in the water molecule. Then they build such molecule on the interactive board using the Lewis structure for hydrogen and oxygen.

2. The teacher plays the presentation „The formation of a hydrogen chloride molecule”. After the screening the participants explain how hydrogen and oxygen atoms bond.

3. The students read the fragment about a special type of covalent bond, called polar covalent bond (polar atomic bond). They define this concept.

4. Participants analyze formulas of illustrative chemical compounds built from molecules with polar covalent bonds presented in the table.

5. The teacher asks the students to read the fragment titled „Carbon dioxide molecular structure”. Volunteers or selected students discuss the structure of this molecule using the illustrations in the abstract.

6. The teacher divides the students into groups. He distributes the ball‑and‑ball models and asks the students to build the models of molecules of hydrogen chloride, ammonia and carbon dioxide. The teacher makes sure that the task have been correctly completed and gives feedback.

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

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. Carry out task number 3.1.

The following terms and recordings will be used during this lesson

Terms

Texts and recordings

Polar covalent bonds

The electron pair between the atoms of hydrogen and chlorine in the hydrogen chloride molecule does not belong equally to both atoms, but is shifted towards the one that more strongly attracts electrons, in this case – towards the chlorine atom. The described bond is a special type of covalent bond, called polar covalent bond (polar atomic bond).

The polar covalent bond is formed between atoms belonging to different nonmetals. They share electrons, and the formed bonding pair or pairs of electrons are shifted towards the atom with a greater electron attracting capacity. Most often it is an atom with a higher number of electrons on the last energy level.

Atoms of various nonmetals can share more than 1 pair of electrons. An example of a chemical compound in whose molecules this process occurs is carbon dioxide. Its molecules are composed of 2 oxygen atoms connected to one carbon atom.

The carbon atom is in the 14th group of the periodic table and its last electron energy level is formed by 4 electrons. Oxygen atoms have 6 valence electrons. Each of the atoms in the carbon dioxide molecule complements its last energy level to 8 electrons: oxygen atoms give 2 electrons each for shared use with a carbon atom, and a carbon atom shares also 2 electrons with each of them. It can be calculated that for the formation of bonds, oxygen atoms use 2 electrons, while the carbon atom – a total of 4 electrons.

A molecule of carbon dioxide has the following molecular formula: ${\text{CO}}_{\text{2}}$.

The atoms of oxygen and carbon differ in the ability to attract electrons, the oxygen atom has stronger properties in this respect. For this reason, in the carbon dioxide molecule, bonding pairs of electrons are closer to the atoms of oxygen.

• The chemical bond bind atoms together.

• When atoms are connected by a covalent (atomic) bond, they share 1, 2 or maximum 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 nonmetals form covalent bonds.

• Atoms belonging to different nonmetals form polar covalent bonds.

• Structures built of atoms connected by a covalent (atomic) bond are called molecules.

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

• In the molecules: $\text{HCl}$, ${\text{H}}_{\text{2}}\text{O}$, ${\text{CO}}_{\text{2}}$, ${\text{NH}}_{\text{3}}$ there are polar covalent bonds, formed by common pairs of electrons located closer to atoms with a greater number of valence electrons.