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Page 38

1. mass&atomic number

   • mass number
     • total number of protons and neutrons in the atom
   • atomic (proton) number
     • the number of protons in the atom
   • example
     • 23 Na 11
       • 23 is the mass number
       • 11 is the atomic number
       • Na is the element symbol
       • really, the 23 would be on the left top corner and the 11 on right bottom corner like on the periodic table
       • 23-11 = 12 = NUMBER OF NEUTRONS
   • number of neutrons = mass number - atomic number

2. Isotopes

   • these are atoms of the same element that have different numbers of neutrons
   • they have the same atomic number but a different mass number
   • e.g
     • chlorine has 2 isotopes
       • 35 Cl 17
         • 17 protons
         • 17 electrons
         • 18 neutrons (35 - 17)
       • 37 CL 17
         • 17 protons
         • 17 electrons
         • 20 neutrons (37-17)
         • 37 = mass number

3. relative atomic mass

   • relative atoms mass of an element is found on the periodic table
   • is the larger number shown for each element
   • 16 O 8
     • 16 is the relative atomic mass

4. relative formula mass

   • relative formula mass of a compound is the relative atomic masses of all its elements added together
   • to calculate it you need to know..
     • the formula of the compound
     • the atomic mass of all atoms involved
   • e.g
     • H2O
       • (2x1) + 16
       • 2 + 16 = 18
       • write the formula
       • subsitute the relative atomic mass
       • calculate the relative formula mass

5. BIIGGER NUMBER IS ALWAYS THE MASS NUMBER!!!!!!!!!!!!!!!!!!!!!!!!!!!