What do chemical words mean? Exploring key terms | 14-16 years

Working through a series of statements, students clarify their ideas about some key terms relating to chemistry and chemical processes.

This resource explores the following misconceptions:

• A substance cannot be a gas or a mixture.
• A pure substance is something that occurs in nature.
• An element is made up of one type of atom only and cannot be split further.
• A compound has the combined properties of the elements from which it is made.
• Atoms show the macro properties of an element.
• Molecules are always formed when atoms combine.
• A molecule always contains different kinds of atoms.

Learning objectives

Students will be able to:

• Understand the use of basic terms: substance, pure, element, compound, atom, molecule.

Sequence of activities

Introduction

Project or display a picture of the girl pop group Atomic Kitten and ask the students what the word ‘atomic’ means.

Explain that:

• They are going to comment on a selection of definitions for a number of basic chemical words.
• Their correct understanding of these terms is the learning objective.

Activity: stage 1

 Give a worksheet to each student. Ask them to work individually to:

• Look at the twelve questions on the worksheet.
• For each question, place a tick in one of three boxes.
• Explain the reasons for their choices.

Use ‘traffic light’ cards or ‘thumbs up’ to gain class views about each of the definitions:

• Green if they think a statement is correct.
• Red if they think it is wrong.
• Yellow if they are unsure.

Activity: stage 2

Without commenting on the responses, bring students together into groups of four. Circulate and support while they:

1. Compare their answers.
2. Discuss any alternative responses or uncertainties within the group.
3. Share out the role of group spokesperson (each student takes three questions).

Plenary

Organise a plenary. Ask:

1. Spokespersons from different groups to comment on the definitions.
2. Other groups to add to these comments.
3. Supplementary questions, if necessary, to make explicit the issues raised.

Before finishing

Allow time for students to add to their worksheet in the light of what they have heard.

Feedback

Take in student worksheets and comment on ideas that have been clearly and accurately expressed. Identify where students need to develop their ideas further.

Commentary

A familiar image in an unusual context enlivens the explanation of the learning objectives and stimulates thinking.

As they share ideas, in groups, students articulate their ideas and clarify their understanding. This gently promotes self assessment.

The extent of remaining misconception can be gauged and dealt with during the plenary but the quality of questioning is important here.

Individual reflection, by students, is a distinct task at the end of the session. This is later supported by teacher comments confirming progress and helping with the next steps.

Equipment

• Set of traffic light cards
• Image of band Atomic Kitten

Explanatory notes

The aim of the activity is to encourage students to think about the given definitions. Which box they tick is much less important than their reasons.

Questions 1 and 2 probe ‘substance’. The questions identify students who do not think that the term describes gases or mixtures.

Questions 3 and 4 probe ‘pure’ in a chemical context. The questions identify students who, for example, think that rock salt is pure because it occurs naturally but think that the sodium chloride obtained from it is not pure because it has undergone chemical processing.

Questions 5 and 6 probe ’element’. Question 5 should give rise to a discussion about isotopes. Question 6 may give rise to a discussion about electrons, protons and neutrons.

Question 7 and 8 probe ’compound’. Question 7 should highlight the idea that compounds can be made up of atoms from two or more elements. Question 8 tests understanding that a compound has its own properties which may be different from those of its constituent elements.

Question 9 and 10 probe ‘atoms’. Question 9 checks whether students realise that, in some cases, molecules of elements rather than atoms are involved in chemical reactions. Question 10 focuses on the particularly difficult concept for many students that the macro properties of elements may not be shown by individual atoms, for example, shininess, hardness or colour.

Questions 11 and 12 probe ’molecules’. Question 11 raises questions about the formation of ions rather than molecules and the idea that molecules may contain more than two atoms. Question 12 checks whether students realise that atoms of the same element can also form molecules.

Answers

1. A substance is a name to describe solids and liquids, but not gases.
   • Wrong. The word substance can be used to include gases as well as solids and liquids.
2. A substance is a name to describe elements and compounds, but not mixtures.
   • Wrong. Many commonly occurring substances are mixtures.
3. A pure substance is a name to describe something that is found naturally. It has not been chemically processed in any way.
   • Wrong. The purity of a substance refers to its composition, not how it is found or whether it has been processed.
4. A pure substance is a name to describe something that is made up of one kind of substance, not a mixture of two or more substances.
   • Correct.
5. An element is made up of only one kind of atom.
   • Correct. This definition does not allow for isotopes.
6. An element cannot be split into simpler substances.
   • Correct. This definition does not take account of sub-atomic particles like electrons, protons or neutrons.
7. A compound is made of two elements mixed together.
   • Wrong. A compound may be made up of more than two elements combined, not mixed, together.
8. A compound has the combined properties of the elements from which it is made.
   • Wrong. A compound has its own set of properties which may be very different from the properties of the elements from which it is made.
9. An atom is the smallest part of an element that takes part in a chemical reaction.
   • Wrong. In the case of many non-metals the molecule, rather than the atom, is the particle which is involved in chemical reactions.
10. An atom is the smallest particle of an element that still shows the chemical properties of the element.
    • Wrong. Most chemical properties are not exhibited by individual atoms.
11. A molecule is what we get when two atoms bond together.
    • Wrong. Molecules often contain more than two atoms.
12. A molecule always contains different kinds of atoms.
    • Wrong. It is possible to have molecules containing the same kind of atoms.