difference of Relative Abundance & Relative Isotopic Mass?

relative atomic mass(RAM) = relative isotopic mass
= average isotopic mass of all kinds of natural isotopes of that element on the carbon-12 scale.
姐係好似carbon咁, 佢有兩隻isotopes, C-12同埋C-13.
i.e. 1個C-12 atom有mass no.(no. of protons + neutrons) = isotopic mass = 12
1個C-13 atom有mass no. = isotopic mass = 13
(isotopic mass姐係果隻isotope嘅mass number...好易姐= =)

跟住再講Relative Abundance & Relative Isotopic Mass
1. relative abundance = the distribution of isotopes in nature of an element
好似chlorine咁, 佢有兩隻isotopes, Cl-35同Cl-37.
relative abundance of Cl-35 = 75.5%
relative abundance of Cl-37 = 24.5%
其寅姐係話, 在地球中的眾多的Chlorine裹, 當中75.5%係Cl-35, 24.5%係Cl-37, 因為chlorine得兩隻isotopes, 咁各isotopes嘅relative abundance+埋當然 = 100%啦!

2. 咁最後, relative isotopic mass = 75.5%x35 + 24.5%x37(把各isotopes自己的isotopic mass乘番自己嘅realtive abundance) = 35.5即係Cl嘅RAM