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Science

Chemical reactions

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When elements react, their atoms join with other atoms to form compounds [compound: A compound is a substance formed by the chemical union (involving bond formation) of two or more elements. ]. Chemical bonds form when this happens, which involves atoms transferring or sharing electrons.

Reactions and compounds

New substances are formed by chemical reactions. When elements react together to form compounds their atoms join to other atoms using chemical bonds. For example, iron and sulfur react together to form a compound called iron sulfide.

mixture of powders

Mixture of iron (grey) and sulfur (yellow) powders.

Compounds usually have different properties from the elements they contain.

Ionic bonds

Chemical bonds involve electrons from the reacting atoms. Compounds formed from metals and non-metals consist of ions. Ions are charged particles that form when atoms (or clusters of atoms) lose or gain electrons:

  • metal atoms lose electrons to form positively charged ions
  • non-metal atoms gain electrons to form negatively charged ions

The ionic bond is the force of attraction between the oppositely charged ions. This animation shows how ions form when sodium atoms react with chlorine atoms to form sodium chloride.

Covalent bonds

Compounds formed from non-metals consist of molecules. The atoms in a molecule are joined together by covalent bonds. These bonds form when atoms share pairs of electrons.

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