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Compounds and mixtures

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Compounds

Atoms of different elements can join together in chemical reactions to form compounds. For example hydrogen and oxygen are elements. They react together to form water, a compound.

There are countless different ways for the elements to join together, and millions of compounds are known.

Properties of compounds

The properties of compounds are usually very different from the properties of the elements they contain. For example hydrogen and oxygen are both gases at room temperature, but water is a liquid.

The reaction between iron and sulphur to make iron sulphide is often used in school to study elements and compounds. Look at the animation to remind you what happens in this reaction.

Creating iron sulphide

A test tube filled with a mixture of iron and sulfur

A test tube is filled with a mixture of iron and sulfur.

The table compares the properties of iron and sulphur (the two elements), and iron sulphide (the compound).

  Element Element Compound
 

iron

sulphur

iron sulphide

colour silvery grey yellow black
is it attracted to a magnet? yes no no
reaction with hydrochloric acid hydrogen formed no reaction smelly hydrogen sulphide formed

Chemical bonds

The atoms in a compound are chemically joined together by strong forces called bonds. You can only separate the elements in a compound using another chemical reaction. Separation methods like filtration and distillation will not do this.

Iron + Sulfur = Iron sulfide.

Compounds form when atoms join together in a chemical reaction

Activity

Compounds and mixtures activity

How will you react to this activity?

Play

Elemental

Can you conquer the elements?

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