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

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