Topic: Ionic bonds - ionic compounds

Target group

Elementary school student (grades 7. and 8.)

Core curriculum:

Elementary school. Chemistry.

II. Internal structure of matter. Student:

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;

11) uses the concept of an ion (cation and anion) and describes how the ions are formed; determines the charge of metal ions (e.g. Na, Mg, Al) and non‑metals (e.g., O, Cl, S); describes the formation of ionic (e.g., NaCl, MgO).

General aim of education

The student explains the mechanism of ion‑binding formation on the example shown

Key competences

• communication in foreign languages;

• digital competence;

• learning to learn.

Criteria for success
The student will learn:

• to explain what an ion, cation, anion are;

• to show how atoms form from atoms;

• to describe how ionic bonds are formed;

• to compare the properties of ionic and covalent compounds.

Methods/techniques

• expository

  • talk.

• activating

  • discussion.

• 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;

• methodician or green, yellow and red cards;

• periodic table of elements.

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, in order to remind students of the messages from previous classes, conducts a talk: what is electronegativity, ion, cation, anion, what charge values can take the ions of the indicated elements.

2. The teacher displays the table „Comparison of construction characteristics of selected atoms and their ions” from the abstract - analysis, talk.

3. The lecturer presents the presentation „Formation of a hydrogen chloride molecule”. Then he presents on the multimedia table the mechanism of ion formation from sodium and chlorine atoms - he explains what it is about.

4. The lecturer discusses the structure of ionic compounds using the example of sodium chloride, displaying the „Crystal model of sodium chloride” on the multimedia board and the table „Construction of exemplary ionic compounds” from the abstract - analysis and talk..

5. The lecturer explains the influence of the type of binding on the properties of the chemical compound, presenting the table „boiling points and melting of exemplary ionic and covalent substances” from the abstract - analysis is under way, talk.

6. At the end of the lesson, the teacher asks students to do interactive exercises - individual work.

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. Write a short note about the topics covered in the lesson.

The following terms and recordings will be used during this lesson

Terms

Texts and recordings

Ionic bonds - ionic compounds

After accepting or donating one or more electrons, the atoms change their size. Cations have a smaller radius than the atoms from which they are formed, while anions – a larger one.

The striving to achieve the electronic configuration of the closest in the periodic table noble gas is the basic cause of chemical bonds formation. Atoms of some elements, in order to achieve the appropriate number of electrons on the last shell, form common electron pairs, others - donate or accept electrons. An example of a chemical compound that can arise from the donation and acceptance of electrons is sodium chloride NaCl i.e. kitchen salt.

The mechanism of ion formation from sodium and chlorine atoms can be described as follows:

Each of the elemental atoms in sodium chloride achieves the electronic configuration of the nearest in the periodic table of noble gas: sodium cation - neon, chloride anion - argon.

Sodium chloride has other properties than sodium and chlorine, the chemical elements from which it was created. Sodium chloride is made up of sodium cations and chloride anions, which as opposite ions attract each other with electrostatic forces. Such connections in chemical compounds are called ionic bonds.

Ionic bond is a type of chemical bond that arises as a result of attracting ions with opposite signs. The chemical compounds in which ionic binding occurs are said to be ionic compounds. Ions with the same charge repel each other, so they can not be next to each other. For this reason, in the ionic compound, cations and anions are arranged alternately. The structure they form is called an ionic crystal. In the ionic compound crystal, each cation is surrounded by anions, and each anion – by cations.

Ionic compounds are not made up of ions with opposite signs. These ions are attracted each other by the action of electrostatic forces. Ionic compound – sodium chloride – at room temperature is a solid substance consisting of alternating sodium and chloride ions. The numbers of cations and anions in the crystals of the ionic compounds are such that, as a result, the crystal is electrically neutral (not charged with an electric charge). In the case of sodium chloride for one sodium cation ${\text{Na}}^{\text{+}}$ there is one chloride anion ${\text{Cl}}^{-}$. Molecular formula of this compound is $\text{NaCl}$. Record:${{\text{Na}}^{\text{+}}\text{Cl}}^{-}$ emphasizes that this compound is composed of ions.

Ionic compounds are made up of molecules. In their crystals one can distinguish the smallest set of repeating cations and anions, which corresponds to the compound's molecular formula.

Another example of an ionic compound is magnesium chloride, made of magnesium cations ${\mathrm{Mg}}^{2+}$ and chloride anions ${\text{Cl}}^{-}$.

Like every ion compound, magnesium chloride is composed of alternating ions: cations and anions.

The molecular formula of magnesium chloride is: ${\text{MgCl}}_{\text{2}}$.

Ionic structure is also made of aluminum chloride. It is a substance consisting of aluminum cations ${\text{Al}}^{\text{3+}}$ and chloride anions ${\text{Cl}}^{-}$. In the crystal that forms, on 1 tri‑positive aluminum ion ${\text{Al}}^{\text{3+}}$ there are 3 mono‑negative chloride ions ${\text{Cl}}^{-}$. Molecular formula of this compound is ${\mathrm{AlCl}}_3$.

Ionic bonds are formed between metals and some non‑metals.

Chemical compounds made of ions differ from compounds that exist in the form of molecules. Ionic compounds (containing ionic bonds) are formed as a result of interaction of metals with non‑metals. However, covalent compounds (containing covalent bonds) arise from non‑metals.

Ionic compounds at room temperature are solid substances with high melting and boiling points. Under the same conditions, some covalent compounds are gases, others – solids, and still others – liquids. They usually have much lower boiling and melting points than ionic compounds. Most ionic compounds, unlike covalent ones, dissolve very well in water.

• Ionic compounds are composed of alternating cations and anions that form an ordered structure called an ionic crystal.

• In an ionic compound crystal, ions with opposite signs attract each other as a result of the action of electrostatic forces.

• Covalent compounds usually consist of molecules.

• Ionic compounds most often have higher boiling and melting points in relation to covalent compounds; they are also usually more soluble in water compared to substances made of molecules.