The mass of an atom of the element is called the atomic mass. It includes the mass of three subatomic substances that make a single atom which consists of an electron, neutron and proton. It can be expressed in grams but since the atom has a very less mass, It is not possible to express in grams. Instead of grams, we express the mass of an atom in a Unified atomic mass unit whose symbol: u.
One atomic mass unit is equal to one-twelfth of the mass of a one carbon-12 atom. 1 u is expressed as to 1.660538921(73) × 10−27.
How to Find Atomic Mass
Atomic mass is the total of electron, neutron and proton. There are two ways to find the atomic mass:
- Find the atomic mass of an element by going through the periodic table- It can be found by looking at the position of an element in the periodic table.
- By adding electron, neutron and proton of an element.
- Average for all atoms of an elements
How to Calculate Atomic Mass of Isotopes
The weighted average of the isotopes of the element is the atomic mass of an element. Isotopes are the only atoms that have the same atomic number that is same no. of the proton but not the same number of neutrons.
Method to Find Average Atomic Mass
The sum of the mass of isotopes of the elements is the average atomic mass; they are multiplied by their natural abundance. f1M1 + f2M2 + f3M3 … is the average atomic mass. In this f is a fraction to represent the natural abundance of an isotope. M is the mass number of the isotope.
It is simple to find the average atomic mass of an element in the periodic table. When you are having the data of the natural abundance of all isotopes of an element, it is easy to find out the average atomic mass.
How to Find Relative Atomic Mass
- Relative atomic mass is equal to (isotope 1 mass × isotope 1 abundance + isotope 2 mass × isotope 2 abundance + …) ÷ 100
- Relative atomic mass of chlorine is;
Relative atomic mass = (35 × 75 + 37 × 25) ÷ 100
= (2,625 + 925) ÷ 100 = 35.5