revision

revision

1. Ions

   • ions are formed when atoms gain or lose electrons.
   • metal atoms lose electrons from their outer shell to form positive ions.
   • non-metal atoms gain electrons into their outer shell to form negative ions.
   • the number of electrons lost or gained is the same as the as the charge of the ion
   • if 2 electrons are lost, the particle now has 2 more protons than electrons. so the charge is 2+
   • if 3 electrons are gained, the particle now has 3 more electrons than protons. so the charge is 3-
   • group 1 and 2 elements are metals. they lose electrons to form positive ions
   • group 6 and 7 elements are non-metals.