Compounds
6 Minutes
Compounds explained for kids: learn how elements combine to form substances with new properties through everyday examples. An English science lesson.
- Pure substances divided into elements and compounds
- How hydrogen and oxygen combine to make water
- How a compound's properties differ from its elements
What this lesson teaches
A compound is a pure substance formed when different chemical elements combine together in a fixed, specific composition. The newly formed compound has entirely different properties and behaviors from the individual elements that make it up.
How matter is classified
Matter makes up everything in the surrounding world, including everyday objects like tables, pens, pencils, salt, and water. Scientists divide all matter into two broad groups: pure substances and mixtures. Pure substances are then split into elements and compounds. While an element consists of only one single type of atom or molecule, a compound forms when different elements bond together chemically.
How properties change
- When different elements chemically unite to form a compound, their original characteristics change completely.
- Hydrogen gas burns easily and oxygen also burns, yet when they join chemically, they create water, which actually puts out fires.
- Pure sodium metal explodes vigorously when dropped into water, but when it combines with chlorine to form sodium chloride, or common salt, it simply dissolves without catching fire.
- Just as swapping a single letter in a word like some transforms the entire meaning of the word, adding or removing even one element from a chemical compound completely alters its characteristics.
Physical versus chemical changes
Compounds cannot be altered or broken apart by physical actions alone. For instance, no matter how much force is applied to beat or crush water physically, it always remains water. To break down a compound or transform its nature, a chemical process must take place. Introducing a chemical, such as a drop of acid, can alter the properties of a substance and break down the bonds holding its components together.
Examples from everyday materials
- Strong glue starts as a liquid and chemically hardens into a tough solid compound that holds surfaces tightly together.
- Trying to force stuck fingers apart physically is difficult, but applying a chemical like an acid or acetone in nail polish remover breaks down the compound and liquefies it.
- Placing a piece of solid thermocol into nail polish remover causes the thermocol to break down and dissolve rapidly.