What is mass number of an element? How is the mass number related to 1?

The mass number of an element is the total number of protons and neutrons present in the nucleus of an atom.

Every atom has protons and neutrons in its nucleus. The sum of these is called the mass number (A). Protons decide the atomic number (Z), while neutrons add to the mass but not the charge. Mass number shows how heavy an atom is compared to others. It is related to 1 atomic mass unit (amu), because 1 amu is defined as 1/12th the mass of a carbon-12 atom. So, mass numbers are measured in whole numbers and compared with this standard.

Formula:

Mass Number (A) = Number of protons (Z) + Number of neutrons (N)

Example:

• Carbon has 6 protons and 6 neutrons → Mass number = 12
• Oxygen has 8 protons and 8 neutrons → Mass number = 16