How does sodium react with chlorine? | 14-16 years

In this activity, students choose from a bank of phrases to explain what happens when sodium reacts with chlorine.

They work individually to observe and interpret a practical demonstration in terms of atoms, ions, transfer of electrons and formation of an ionic lattice, before anonymously reviewing each other’s explanations.

Learning objectives

Students will be able to:

• Describe and explain what happens when sodium reacts with chlorine.

Sequence of activities

Introduction and demonstration

Demonstrate the reaction of sodium with chlorine, drawing attention to the white solid produced and then share the learning objectives with the students.

Observing and interpreting

1. Give each student a copy of the ’How does sodium react with chlorine?’ sheet, a hand lens and a small amount of solid sodium chloride. Ask them to look at the sample. (Demonstrate this to the whole class if a flexible necked camera linked to a projector is available.)
2. Ask a selection of students what they have seen:
   • In the reaction.
   • In viewing the solid.
3. Ensure that everyone has a common shared description to write on their ’How does sodium react with chlorine?’ sheet.
4. Ask students to explain, on their ’How does sodium react with chlorine?’ sheet, what happens when sodium reacts with chlorine in terms of atoms, ions, transfer of electrons and formation of an ionic lattice. If necessary, provide some ‘scaffolding’ with the ‘Useful words, phrases and diagrams’ sheet.

Anonymous peer assessment

1. Allocate a number to each student to:
   • Write on their sheets.
   • Remember without sharing with others.
2. Take in the ’How does sodium react with chlorine?’ sheets.
3. Randomly redistribute the sheets. (Students could pick numbers from a hat.)
4. Set the students to write comments on the sheet identifying the good features and suggesting where it could be developed.
5. Collect in the ’How does sodium react with chlorine?’ sheets and return to the original owner.
6. Ask the students to review the comments that have been written about their work.

Summarising

Use questions to draw together and summarise the explanation of the reaction of sodium and chlorine in terms of:

• Original electron structure of sodium and chlorine atoms.
• Transfer of an electron resulting in positive sodium ions and negative chloride ions.
• The formation of a giant lattice structure in which there is a strong electrostatic attraction between oppositely charged ions ‑ called an ionic bond ‑ which extends throughout the structure of ions.

Extend the ideas to the reaction of any Group 1 element with any Group 7 element.

Allow students to add to what is already on their ’How does sodium react with chlorine?’ sheet.

Feedback

Make sure that students write their name on their ’How does sodium react with chlorine?’ sheet. Take in the sheets and comment on:

• The achievement illustrated by what they have written.
• Ways in which they can develop their explanation further.

Commentary

The initial demonstration is a stimulus, the basis of the session and a way of elaborating on the learning objectives.

Questions and questioning technique are crucial to developing and ensuring that everyone understands what happens in the reaction.

The anonymous peer assessment is the second key feature. Students may need advice about how to be helpful in their comments. Good practice on the part of the teacher, in previous activities, will give a lead.

Another opportunity to exercise that good practice is included here.

Practical notes

Equipment

For the demonstration

• Flexible necked camera linked to data projector or TV screen

For each student

• Hand lens
• Small sample of solid sodium chloride

Health, safety and technical notes

• Read our standard health and safety guidance.
• Wear eye protection.
• For the demonstration, consult the safety instructions included with the procedure for heating sodium in chlorine in Heating group 1 metals in air and in chlorine.
• It is the responsibility of the teacher to carry out an appropriate risk assessment for the demonstration.

Answers

Explanation of what happens when sodium reacts with chlorine:

• A sodium atom has one electron in the outer shell.
• A chlorine atom seven electrons in the outer shell.
• A sodium atom loses an electron to a chlorine atom.
• The sodium atom becomes a positive sodium ion.
• The chlorine atom becomes a negative chloride ion.
• Both sodium ions and chloride ions have full electron shells.
• The sodium ions and chloride ions form an ionic lattice.
• An ionic lattice is one example of a giant structure.
• There are strong electrostatic attractions between the oppositely charged ions in an ionic lattice.