Difference Between Atomic Mass and Atomic Weight

Atomic mass and atomic weight do not mean the same but still some people use the terms interchangeably.

Atomic mass:

The total number of neutrons and protons of an atom is called atomic mass. Electrons are not counted and can be neglected as their size is very small. The atomic mass unit is dalton. It is represented as Da and is the standard unit used to indicate mass of an atom. Atomic mass of elements differs as it depends on the number of protons and neutrons in a particular element.

Atomic weight:

A single element can have several isotopes. To calculate atomic weight it is necessary to consider masses of isotopes. The percentage of isotopes may differ. While calculating atomic weight, isotope relative abundance and isotope mass has to be considered.

To make you understand how atomic mass and atomic weight are different from each other, here are the some of the major differences between atomic mass and atomic weight:

Difference between Atomic mass and Atomic weight



It is the sum of neutrons and protons present in an atom

Average of ratio of atoms, present in an element

Isotopes are not included in calculation

Isotopes are included in calculation

Calculated value is a whole number

Calculated value may or may not be a whole number

Analysis is done by mass spectroscopy

Analysis is done by mass spectroscopy