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1. Isotopes

   • Not all atoms of an element have the same number of neutrons. Atoms of same element with different masses are isotopes.
   • Proportion of each isotope is fixed, and same in both pure element and compounds.
   • Isotopes have same number of electrons, and react in same way

2. Relative formula mass

   • To work this out from a compound you find atomic mass of each, by the number present in the formula.

3. Noble gases

   • Nobles gases (group 0) are unreactive because they have full outer shell. When atoms combine to make a compound their outer electrons are shared, gained or lost until each atom has noble gas electronic configuration

4. Ionic bonding

   • When a metal reacts with a non-metal, the metal atoms loose electrons and because a positive ion, but when non-metal gains then it becomes negative ion.
   • opposite charged ions are electrostatically attracted.