How to play Atom Detective
Atom Detective is a free KS3 chemistry game about elements, compounds and mixtures. Each question shows you a substance. You decide which of the three it is, then tap Element, Compound or Mixture.
The early questions use formulas made of capital letters. Each letter stands for one kind of atom, so A and B are two different kinds. A small number after a letter tells you how many of that atom are joined in one particle. A plus sign means two separate kinds of particle that are not joined to each other.
Later questions drop the letters. Instead, you read a short description of the particles, such as pairs of atoms or atoms packed into a block. You sort it using the same rules.
A round has ten questions, and they get harder as you go. Tick the harder start to skip the easiest ones. Each right answer scores 10 points. A 30-second timer runs on each question, and the practice switch turns it off. On a keyboard, press 1, 2 or 3 to answer and Enter for the next question. Your best score stays on this device, and the harder start keeps a separate best.
The science behind elements, compounds and mixtures
KS3 science uses a simple model of matter called the Dalton model. In this model, everything is made of tiny particles called atoms. There are different kinds of atom. This game uses that simple model and nothing more.
An element is a substance made of only one kind of atom. The atoms can sit on their own, or they can join up in pairs or bigger groups. As long as every atom is the same kind, the substance is an element. That is why A and A₂ are both elements.
A compound forms when two or more different kinds of atom join together. Every particle of the compound has the same atoms, joined in the same way. AB, AB₂ and ABC are all compounds, because each particle holds more than one kind of atom.
Chemists write elements and compounds with symbols and formulas. A symbol stands for one kind of atom. A formula lists the atoms in one particle, with a small number to show when there is more than one. This game uses letters in place of real symbols, so you can focus on the rules.
A mixture is different again. It holds more than one substance, but they are not joined to each other. A + B is a mixture of two elements. AB + C is a mixture of a compound and an element. Dissolving makes a mixture too. When a solid dissolves in water, its particles spread out between the water particles.
A pure substance has only one kind of particle, so an element or a compound on its own is pure. A mixture is not pure. These ideas come from two parts of the KS3 National Curriculum for science. One is atoms, elements and compounds. The other is pure and impure substances. KS3 science also teaches ways to separate mixtures, such as filtration, evaporation, distillation and chromatography.
Tips for sorting elements, compounds and mixtures
- Look for a plus sign first. A plus sign always means a mixture, whatever sits on either side of it.
- With no plus sign, count the different letters. One letter means an element. Two or more means a compound.
- Ignore the small numbers when you count. A₂ still has only one kind of atom, so it is an element.
- In the descriptions, look for the word "joined". Different atoms joined in every particle means a compound.
- Loose atoms of different kinds, or two kinds of particle, mean a mixture.
The trickiest question has two kinds of particle made of the same two atoms. Each particle is a compound, but together they make a mixture. Slow down on that one.
Use this in the classroom
Atom Detective suits Years 7 to 9 when you teach atoms, elements and compounds. It also works as revision before a test. A round takes about five minutes.
Before you play, draw three boxes on the board with coloured circles for atoms. Draw loose single atoms in one, joined pairs of two colours in the next, and a jumble of both in the third. Ask the class to name each box. Then play a round on the board and let students vote before you tap.
The letter formulas make a good bridge to real chemical formulas. After a round, ask students to draw the particles for AB₂ or A₂ + B with circles and sticks. Students who finish early can try the harder start, where every question uses a description.
Students can turn the timer off with the practice switch. Nobody has to sign up. For more lesson ideas, see our page for teachers. The what we collect page sets out what the site keeps.
Similar games
Once letters feel easy, meet the real symbols in the Periodic Table Challenge. For KS3 physics, Force Sort asks if forces are balanced, and the Food Web Builder covers KS3 biology. The chemistry games page lists more.
Questions people ask
Students and teachers often ask these questions about atoms and substances.
What is the difference between an element, a compound and a mixture?
An element has only one kind of atom. A compound has two or more kinds of atom joined together in every particle. A mixture has two or more substances that are together but not joined to each other.
Why is a formula like A₂ an element and not a compound?
The small 2 means two atoms are joined in each particle. Both atoms are the same kind, so the substance is still an element. A compound needs at least two different kinds of atom joined together.
How can you tell a compound from a mixture?
In a compound, different atoms are joined together inside each particle. In a mixture, the substances sit side by side without joining. A formula with a plus sign in this game shows a mixture.
Which part of KS3 science does this game cover?
It covers atoms, elements and compounds, and pure and impure substances. Those are both in the chemistry section of the KS3 National Curriculum for science. The game keeps to the simple Dalton model of atoms.