Lesson 3 of 5

Compounds

Goal: Describe how a compound differs from the elements in it.

Puzzles for this lesson

Word search0 of 7 foundCrossword0 of 41 letters

A compound is a substance made of two or more elements, chemically joined together.

Swipe to see two elements and the compound they make.

A lump of sodium metal, cut to show a shiny silver face

Element

Sodium

A soft, shiny metal.

It fizzes violently in water.

A glass flask full of pale green chlorine gas

Element

Chlorine

A pale green gas.

It is poisonous.

A dish of white salt crystals

Compound

Sodium chloride

White crystals.

It is table salt, the salt you put on food.

A compound has different properties from the elements in it.

  • A compound is made in a chemical reaction. Atoms of different elements join together.
  • You cannot just pick the elements back out. A magnet or a filter will not do it. It takes another chemical reaction.
  • The recipe never changes. Every molecule of water has two hydrogen atoms joined to one oxygen atom.
HHHH+OOHHOHHO hydrogenoxygenwater

Hydrogen burns in oxygen to make water. No atoms are made and none are lost. They are rearranged and joined in a new way.

A heap of grey iron filings and a heap of yellow sulfur powder, with a bar magnet beside them
Iron and sulfur. Iron is a grey metal that a magnet attracts. Sulfur is a yellow powder. Test them in the activity below.

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Key words in this lesson

Atom The smallest particle of an element that can exist

Element A substance made of only one type of atom

Compound Two or more elements chemically joined together

Molecule A group of two or more atoms joined together

Chemical reaction A change that rearranges atoms to make new substances

Chloride A compound of an element with chlorine

Sodium chloride The compound in table salt

For teachers: AQA 3.5.4 · Pearson Edexcel 14.1 · Cambridge 7Cm.04