Topic: Valence of chemical elements pt 3

Target group

Elementary school student (grades 7. and 8.)

Core curriculum:

Elemntary school. Chemistry.

II. Internal structure of matter. Pupil:

14) draws a structural formula of a molecule of a two‑element compound (with covalent bonds) with known valences of elements;

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

General aim of education

The student creates names of oxides and uses the element's valence to determine the structural formulas of the two‑element compounds

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:

• define the concept of valence;

• 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;

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

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

• recognize an oxide based on its total formula;

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

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

Methods/techniques

• expository

  • talk.

• activating

  • discussion.

• 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;

• ball‑and‑ball models.

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 rules for writing summary formulas based on names. He gives some sample names of oxides - willing write their summary formulas on the board.

2. The teacher displays the table „Sample names of oxides” from the abstract - analysis and discussion are under way.

3. The lecturer discusses the principles of creating names of oxides on the basis of their summary models. Displays the presentation „Creating the name of a chemical compound based on its summary formula”. Then presents the table „Valence of selected elements in oxides” - analysis and discussion are under way.

4. The students and the teacher analyze the table „Names of exemplary oxides of elements of selected groups of the periodic table” - discussion continues.

5. The teacher explains the principles of determining summary models based on names. It displays the following instructions: „Writing the barium oxide total formula”, „Saving the sum formula of nitric pentoxide” from the abstract and discusses them.

6. Students learn the principles of creating structural formulas of covalent compounds based on the knowledge of the valence of elements. The teacher writes down a few examples on the board, eg nitric(II) oxide , sulfur dioxide and explains them.

7. The teacher divides the students into groups, distributes plasticine models. He asks for building particle models for elements with their valences previously written on the table, eg Al(III) and O(II), Li(I) and O(II), Cr(VI) and O(II), Fe(II ) and O(II), N(IV) and O(II), Mn(VII) and O(II). Monitors the work of students.

8. 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

Valence of chemical elements pt 3

Oxygen compounds with other elements are called oxides. The only exception is the oxygen‑fluorine compound, called oxygen fluoride. In all oxides, oxygen has a valency of two. On this basis, knowing the oxide formula, we can determine the valency of elements in oxides.

The names of oxides are double‑segmented. The first term is the name of the element in the genitive and the second – the word oxide e.g. sodium oxide. Many elements create several oxides in which their valency is different. An example is the compounds of lead with oxygen with the following molecular formulas: $\text{Pb}{\text{O}}_{\text{2}}$ and $\text{PbO}$.
In the first oxide, lead has a valency of four, in the second - two. Therefore, to uniquely determine the type of compound, e.g. oxide, its name often gives the valency of the element connected with oxygen. The compounds of the formulas discussed above $\text{Pb}{\text{O}}_{\text{2 }}$ and $\text{PbO}$ are respectively: lead(IV) oxide and lead(II) oxide. Oxygen valency is not determined in the names of oxides, since it is always two (II).

By creating the names of metal oxides belonging to groups 1st and 2nd, their valency is not given, because these elements always have only one characteristic valency in chemical compounds: metals from 1st group - one, from 2nd group – two. A similar principle applies to aluminum: due to the fact that this element has a valency of three, it has been assumed not to give its valency in the name of the compounds.

Based on the full name of the oxide, you can easily write its molecular formula. Remember that oxygen valency in these compounds is two. The valency of the second element must be known or it is given in the name. If the element belongs to the 1st group of the periodic table, its valency will be equal to one, if it is the element located in the 2nd group, it will have the valency equal to two.

We determine the valency of particular elements that make up the oxide:

We write the molecular formula of barium oxide: BaO

We determine the valency of particular elements that make up the oxide:

We are writting molecular formula of dinitrogen pentoxide: NIndeks dolny 2₂OIndeks dolny 5₅

Determining the structural formula of a compound molecule based on its molecular formula is not always possible. For example, without knowing about the existing connections between individual atoms, we will not draw a formula of a compound molecule consisting of three elements with a molecular formula ${\text{H}}_{\text{2}}\text{S}{\text{O}}_{\text{4}}$. In the case of two‑element compounds, it is possible if you know the valency of both elements. The easiest way to draw a formula of a molecule made of two atoms. An example is a molecule created by combining nitrogen and oxygen, the valency of which is two. It has the following structural formula:

$\text{N = O}$

Both atoms of elements have a valency equal to two and form two bonds each.

• Oxygen in oxides has valency equal to two. Based on this information and compound molecular formula, valency of the second element in the connections with oxygen can be determined.

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

structural formula, valency