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Lemon juice, vinegar and car battery acid behave the same way despite having nothing else in common. Work back to the particle they all release, in an interactive playground.

pH is one number reporting how many hydrogen ions a solution contains, and each step is a factor of ten. Place six regions on the scale in an interactive playground.

Acids react with metals, with bases and with carbonates, and every one of those produces a salt. What differs is what comes out alongside it. Sort the three in an interactive playground.

Mixing an acid and a base gives a salt in seconds, so why does getting a dry sample of it take four more stages? Each one answers a problem the last created.

A dilute strong acid and a concentrated weak acid are completely different things, and the words are not interchangeable. Follow both questions from one bottle in an interactive playground.

An atom is three kinds of particle in two places, and overwhelmingly empty space. Label a lithium atom and its magnified nucleus in an interactive playground.

An atom has three kinds of particle, and only one of them decides which element it is. Eliminate the other two step by step in an interactive playground.

Atoms are built from whole particles, so a mass of 35.5 looks impossible. Follow both isotopes of chlorine to the weighted average in an interactive playground.

Lithium, sodium and potassium behave almost identically, and that is not a coincidence. Work back from the repeating pattern to how electrons are arranged in shells.

The periodic table is not a chart to memorise. Its rows are shells and its columns are outer electrons. Sort three groups by what their atoms have in common in an interactive playground.

Almost every element forms compounds and a handful do not. Work out what the exceptions have in common, and the reason atoms bond follows, in an interactive playground.

An ion’s charge is not a fact to memorise: it follows from the outer electrons, and the formula of the compound follows from the charges. Work it through in an interactive playground.

Two atoms meet with unfilled shells, and what happens next depends on whether either can give electrons away. Follow both routes from one starting point in an interactive playground.

Water has strong covalent bonds and melts at 0 °C; salt melts at 801 °C. The answer is that melting never breaks a bond inside a molecule. Trace what a lattice explains in an interactive playground.

A metal is a lattice of positive ions sitting in electrons that belong to no single atom — which is why it bends where salt shatters. Label the structure in an interactive playground.

An element is not defined by how it looks or behaves — it is defined by the fact that nothing breaks it down into anything simpler. Follow the reasoning step by step in an interactive playground.

Every substance is an element, a compound or a mixture, and the jar tells you nothing. Sort six sealed samples by what their particles are doing, in an interactive playground.

Stir iron and sulfur together and you still have iron and sulfur. Heat them until they react and the magnet stops working. Follow both routes from the same starting point in an interactive playground.

There is no list of separation methods to memorise. Find the one property the parts of a mixture do not share, and the method chooses itself. Sort six techniques by the difference each one uses.

Filtering, boiling and chromatography all need the parts to differ in something. A compound has one set of properties, so there is nothing to exploit. Follow the reasoning step by step in an interactive playground.