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i can say the easy trick to remember the atomic masses for first 20 elements
The atomic masses of elements like He, Li, C, N, O, Ne, Si, S, Cl, Ca are double the atomic number.
and  for 
Be, B, F, Na, Mg, Al, P, Ar and K  double the atomic number and add 1.
this is the trick i know hope it helps
plz mark  it the best!!!!!!!!!
1 5 1
See atomic mass of an element is equal to the no. of protons in the atom + no. of neutrons in the atom
also no. of protons = atomic no. of element
1 5 1
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