Atomic Mass

Question 1 How is the size of an atom indicated?

Question 2 Define atomic mass unit?

Question 3 What is the mass of hydrogen atom?

Question 4 Name the element used as a standard for atomic mass scale?

Atomic Mass of an Element

Actual masses of the atoms of the elements are very very small.

For Example : The atom of hydrogen has a mass of 1.6727 x 10^-27 kg. It is not convenient to use such small and complicated figures in our calculation,therefore ,it was necessary to define atomic masses in such a way that we get simple figures for them.

Carbon-12 is that atom of carbon which has 6 protons and 6 neutrons in its nucleus so that so its mass number is 12.

carbon-12 atom has been assigned an atomic mass of exactly 12 atomic mass units.This means that a carbon-12 atom has been assigned an atomic mass of exactly 12u.

Atomic Mass unit = the mass of a carbon – 12 atom

One Atomic Unit is defined as exactly one-twelfth the mass of an atom of carbon-12.

Carbon-12 atom is taken to be the standard.The atomic masses of all other elements are determined by comparing the mass of their atom with the mass of a carbon-12 atom.

The atomic mass of an element is relative mass of its atom as compared with the mass of a carbon-12 atom taken as 12 units.