Topic: The valence of chemical elements pt 2

Target group

Elementary school student (grades 7. and 8.)

Podstawa programowa:

Elementary school. Chemistry.

II. Internal structure of matter. Pupil:

13) determines on the basis of the periodic table the valence (relative to hydrogen and maximal to oxygen) for the elements of groups: 1, 2, 13, 14, 15, 16 and 17;

15) determines for two‑element compounds (eg oxides): a name based on a sum formula, a summary formula based on a name, a summary formula based on valence, a valence based on a sum formula.

General aim of education

The student writes down the summary formulas of two‑element chemical compounds on the basis of information about the valences that make up their elements

Key competences

• communication in the mother tongue;

• communication in foreign languages;

• mathematical competence and basic competences in science and technology;

• digital competence;

• learning to learn.

Criteria for success
The student will learn:

• to define the concept of valence;

• to read from the periodic table the maximum valences of chemical elements of groups 1, 2 and from 13 to 17 of the periodic table in their relationship with hydrogen or oxygen;

• to write summary formulas of two‑element chemical compounds on the basis of information on the valences that make up their elements;

• to determine the valence of one chemical element in a relationship, when the valence of the other is known;

• to recognize an oxide based on its total formula;

• to write the total formula of the oxide, knowing its name;

• to draw structural formulas of two‑element chemical compounds, knowing what is the valence of the elements that make them.

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;

• 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 initiates the lesson by reminding the students of the concept of valence and structural formula - a talk.

2. The lecturer discusses the principles of determining the sum formula of a chemical compound based on the valence of its elements, analyzing calcium oxide. Then it displays the presentations „Determination of the sum formula of potassium oxide based on the valence of elements” and „Determination of the sum formula of sulfur dioxide based on the valence of elements”. After the projection, he analyzes the table „Determination of summary sums of exemplary 2‑element compounds on the basis of information on the valence of elements” - discussion.

3. The lecturer gives the systematic names of oxides of various elements, e.g. magnesium oxide, copper(I) oxide, copper(II) oxide, aluminum oxide, dinitrogen trioxide, nitrogen dioxide, nitric oxide, nitrous oxide, dinitrogen pentoxide, sulfur dioxide, calcium oxide, barium oxide, dichlorine heptoxide , zinc oxide, iron(II) oxide, iron(III) oxide, lead(II) oxide, lead dioxide, and subsequent students write their summary formulas on the board (the others write them in the subject notebooks). If there is a need, students can use the periodic table of chemical elements.

4. The teacher writes on the board the total formula of phosphorus oxide in the form PIndeks dolny 4₄OIndeks dolny 10₁₀. He explains that studies have shown that the molecule of this compound consists of four atoms of phosphorus and ten atoms of oxygen, and the PIndeks dolny 2₂OIndeks dolny 5₅ formula does not reflect this fact. Then he displays on the multimedia board the „Model of the phosphorus oxide molecule” and „Structural formula of the phosphorus oxide molecule” - students analyze it together with the teacher.

5. The lecturer discusses the principles of determining the valence of one of the elements in a two‑element relationship. He presents the instruction „Determination of valence of calcium in a compound of the formula CaClIndeks dolny 2₂, in which the valence of chlorine is one (I)”. Then he gives examples of two‑element compounds. Writes summary formulas on the board with an indication of one valence in a compound, e.g. potassium sulphide, aluminum sulphide, zinc chloride, iron(III) chloride, sulfur dioxide, sodium oxide, magnesium sulfide, copper(II) oxide, tin(IV) oxide, mercury(II) oxide, and students determine the valence of the second element.

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. 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

The valence of chemical elements pt 2

If we know the valence of two elements, which together form a chemical compound, then in practically every case we can determine the total formula of this compound. We do not need to know what kind of bonds exist in a relationship. In many cases, the obtained sum formula is true and well describes the composition of the molecule or the smallest set of repeating ions in the ionic compound. Determining the order of symbols in the summation formula can be a problem. It does not matter if the compound is formed by metal and non‑metal. Then, in the sum formula, we first write the metal symbol, and then, to the right, we insert the symbol of the second element.

One of the simpler ways of defining summary models can be found in the examples.

In the two‑element compound (formed by two elements) one can determine the valence of one element if you know the valence of the other.

If no stoichiometric indexes are present in the compound formula (or in rare cases are equal), elements that form a given compound have the same valence. In the compounds you are currently learning (oxides, chlorides, sulphides), oxygen has two (II), one (I) chlorine and two (II) sulfur.

For example, in a compound of the formula $\text{CuO}$, in which the oxygen valence is two (II), copper has identical valence(II). In sodium chloride $\text{NaCl}$ sodium and chlorine have the same valence – one (I). In other cases, appropriate transformations and calculations should be made. We will get to know the simplest way from the example.

We behave in the opposite way than when determining patterns. This time we transfer the stoichiometric factors „crosswise” over the symbols of elements.

After transferring the index values, we write using Roman numerals:

We check whether the numbers saved above the symbol of the element with known valency are consistent with the content of the task. In our case, this is because chlorine has a valence of one (I). Then the number written above the symbol of the second element determines its valence. For calcium, it is equal to two (II).

We give the answer:

Calcium valency in a compound of the formula CaClIndeks dolny 2₂ it is two (II).

• On the basis of the periodic table, you can determine the maximum valence with respect to hydrogen and oxygen for elements from groups 1 and 2 and 13, 14, 15, 16 and 17.

• The elements in the group 1 of the periodic table in created compounds have a valence equal to one, from group 2. they have a valence two.

• Valence of oxygen in oxides is two. On the basis of this information and the formula of the compound, the valence of the second element in the connections with oxygen can be determined.

• The names of oxides give the valence of the element, which in chemical compounds may have different valences.