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1. atoms

   • The atomic number: the proton number in an atom
   • isotopes have the same proton number but a varying neutron number
   • The isotope Carbon-12 is used when comparison when concerning mass
   • RELATIVE ISOTOPIC MASS: the mass of one atom of an element in comparison to 1/12th of one atom of 12C
   • RELATIVE ISOTOPIC MASS: the mass of an atom of an isotope comparred with the mass of 1/12th of an atom of 12C
   • isotope X abundance/100

2. group 7 "The Halogens"

   • Boiling point increases down the group as there is more Van Der Waals' forces
   • reactivity decreases down the group
   • Chlorine is used for the use of water treatment. But it is a toxic gas
     • the reaction of cold,dilute sodium hydroxide is used to form bleach

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