Chemistry

The chemistry unit at a glance

Chemistry is the study of what everything is made of and how it changes. This unit brings its big ideas together. Everything is built from atoms, and the periodic table arranges the elements so their behaviour makes sense. Atoms join by bonding to form compounds. In a chemical reaction the starting substances change into new ones, yet no mass is ever lost. Acids and bases react in predictable ways. This module gives you an overview of atomic structure, bonding, reactions and the conservation of mass, ready to build on with more detail later.

Chemistry words to know

Learn these before the detail. They name the building blocks and the golden rule of every chemical reaction.

Match the particle or term to its description

Ionic against covalent bonding

Atoms join in different ways. The two you meet most are ionic and covalent bonding, and they produce very different substances.

What holds it together?

A metal reacts with a non-metal, and electrons are transferred from one to the other. Which type of bonding is this?

• Ionic bonding
• Covalent bonding
• Metallic bonding
• No bonding at all

Mass is never lost

One rule underpins every reaction you study: mass is conserved. The atoms in the starting substances are not created or destroyed; they are only rearranged into new substances. So the total mass of the products always equals the total mass of the reactants. If a reaction in an open dish seems to lose mass, a gas has escaped; if it seems to gain mass, a gas has joined in from the air. Count the atoms in, count the atoms out, and they always match.

Pick the true chemistry facts

Select every statement about chemistry that is true.

• An element contains only one kind of atom
• A compound contains two or more elements joined
• Mass is conserved in a chemical reaction
• Atoms are created during a reaction
• A mixture is a single pure substance

Order a neutralisation

Put the steps of neutralising an acid with an alkali in order.

• Start with an acid, which has a low pH
• Add an alkali a little at a time
• The acid and the alkali react together
• The mixture moves towards a neutral pH
• A salt and water are formed
• Check with an indicator that it is neutral

Complete the chemistry facts

The smallest particle of an element is an _____. A substance made of only one kind of atom is an _____. Two or more elements joined together make a _____. The rule that no mass is gained or lost in a reaction is the _____ of mass.

Why a burning candle seems to vanish

A burning candle looks like it destroys matter: the wax slowly disappears. But nothing is destroyed. The wax reacts with oxygen from the air, and the atoms rearrange into new substances, mostly carbon dioxide and water vapour, which drift away as gases. If you could trap and weigh everything, the wax and oxygen you started with would equal the gases you ended with, exactly. The candle does not lose mass; the mass simply leaves as invisible gas. That is conservation of mass in action, and it is why chemists weigh reactions in sealed containers.

Spot the correct chemistry

Tap the TWO statements that are correct chemistry.

• In a reaction the atoms are rearranged, not created or destroyed
• A compound is two or more elements chemically joined
• An element is a mixture of many different atoms
• Burning destroys atoms completely

Work out the mass of products

In a sealed flask, 10 grams of one substance react completely with 5 grams of another. Because no mass is lost, what is the total mass of the products, in grams?

Think like a chemist

Use chemistry ideas to answer each problem.

• A metal reacts with a non-metal by transferring electrons. What kind of substance forms?
• A reaction in an open dish appears to lose mass. What has most likely happened?
• You add an alkali to an acid until the mixture is neutral. What has been made?

Build a chemistry point

Choose the word for each gap to complete one correct chemistry point.

Explain atoms, bonding and reactions

A friend thinks chemistry is just memorising facts. Explain the big ideas that connect it: what everything is made of, how atoms join, and what happens in a reaction.

• Explain what atoms and elements are
• Explain how the periodic table is organised
• Explain the difference between ionic and covalent bonding
• Explain what happens in a chemical reaction
• Explain why mass is conserved