1. Atomic Structure

2.  Atomic number – the number of protons in the nucleus of an atom ( ID of element )  Mass number– sum of protons and neutrons in an atom.  Actual mass- what an atom actually weighs.

3. Actual atomic mass Actual atomic mass  Mass of a proton = 1.0 x 10 -23 g  Mass of a neutron = 1.0 x 10 -23 g 1( 1.0 x 10 – 23 ) g 2( 1.0 x 10 – 23 )g 3 ( 1.0 x 10 – 23 )g

4. Relative atomic mass – the mass of an atom compared to a standard.  if we say protium is one, then deuterium is two and tritium will be three. R-ATM 1 R- ATM 2 R- ATM 3

5. The real standard is carbon-12  a Protium atom is 1/12 the weight of a carbon-12 atom, so it still works out that the relative atomic mass is still one.

6. Atomic Mass  If each element has several isotopes with their own relative atomic masses, what number is put on the periodic table?  Atomic mass ( atomic weight, old school) is the weighted average of all the naturally occurring isotopes of that element.

7. Do the math  Symbol R-atm X % = product  35 Cl 34.969 x 75.53 = 26.41  + 37 Cl 36.966 x 24.47 = 9.045 Atomic mass of Cl = 35.46amu  Move the decimal in the % 2 places to the left before you enter it into the calculator.

8. Alternate set up  (R-atm x % ) + (R-atm x % ) = atomic mass  (34.969 x.7553) + (36.966 x.2447) =35.46  Repeat for as many isotopes that there are for that element.