Ice melting and paper burning are both changes, but they are very different. In this course we separate physical changes from chemical changes, and we learn what elements and compounds are, and how a compound differs from a mixture.
3 lessons, about 1 h 25 min3 simulations10 problems6 practice questionsPython in every lesson
Created by StemPy LabIn a physical change, the physical properties such as state, shape, size, colour or density change, and no new substance is made, so the change can often be reversed. In a chemical change, one or more new substances with new properties are made, and it is usually hard to reverse. A chemical change often shows a gas, a change of colour, a new smell, heat or light, or a new solid. Some changes need a careful look, such as a burning candle, which has both kinds.
An element is a pure substance made of only one kind of atom, and it cannot be broken down into simpler substances by a chemical change. More than a hundred elements are known. Each has a symbol of one or two letters, with a capital first letter, and some symbols come from Latin names, such as Na, Fe and Cu. Most elements are metals, which shine, are malleable, ductile, sonorous and good conductors. Non-metals do not have these properties, and metalloids lie between the two.
A compound is made of two or more elements that are joined in a fixed ratio by mass. It has properties that differ from its elements, and it can be split only by chemical changes. A mixture can have any ratio, and its parts keep their own properties.
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