Question

Trick to remember the atomic masses of first twenty elements of periodic table.

Answer 1

There is only one trick to remeber the atomic masses of first twenty elements that is you should know the atomic number of element then double tje atomic number to get atomic mass but remember it is only applicable to most of the first twenty elements but not all.

Answer 2

first twenty elements are , H, He , LI , Be , B , C , N , O , F , Ne , Na , Mg , Al , Si , P, S , Cl, Ar , K , and Ca
here
except :- Li , Be, B, F, Na , Al , P, Cl , K and Ar all atomic mass number is double the atomic number of it .
example :-
atomic no of CA = 20
so , mass no = 2× 20 = 40

# in Li , Be , B , F , Na , Al , and K
let atomic number of it is x
then mass number of it = 2x +1
example :-
atomic number of Al = 13
so, mass number = 2×13 +1 =27

# for Ar ( argon)
atomic no = x
then mass no =2x +4

# Chlorine
atomic no = 17
mass no = 35.5