Atoms can join together to make compounds

• When elements react, atoms combine with other atoms to form compounds

  • Compounds are substances formed form two or more elements

  • The atoms of each are in fixed properties throughout the compound and they’re held together by chemical bounds

• Making bonds involves atoms giving away, taking or sharing electrons.

• Only the electrons are involved-the nuclei of the atoms aren’t affected at all when a bond is made

• It’s usually difficult to separate the original element of a compound out again

  • A chemical reaction is needed to do this

• A compound which is formed from a metal and a non-metal consists of ions.

  • The metal atoms lose electrons to form positive ions and the non-metal atoms gain electrons to form negative ions.

  • The opposite charges(positive and negative) of the ions mean that they’re strongly attracted to each other.

  • This is called ionic bonding.

    • Examples of compounds which are bonded ionically include sodium chloride, magnesium oxide and calcium oxide

• A compound formed from non-metals consists of molecules.

• Each other shares an electron with another atom-this is called covalent bonding.

  • Examples of compounds that are bonded covalently include hydrogen chloride gas. carbon monoxide and water

• The properties of a compound are usually totally different from the properties of the original elements.

  • For example, if iron and sulfur react, the compound formed is a dull grey solid lump, and doesn’t behave anything like either iron or sulfur

A formula shows what atoms are in a compound

• Just as elements can be represented by symbols, compounds can be represented by formulas.

• The formulas are made up of elemental symbols in the same proportions that the elements can be found in the compound