what is the mass number of an atom

The mass number of an atom is the total number of protons and neutrons present in the nucleus of that atom. It is represented by the symbol “A.” Since electrons have negligible mass, they are not included in the mass number.

Formula:
Mass Number = Number of Protons + Number of Neutrons

For example, a carbon atom has:

• 6 protons

• 6 neutrons

Therefore:
Mass Number = 6 + 6 = 12

The mass number helps identify different isotopes of an element because isotopes have the same number of protons but different numbers of neutrons.

Example:

• Carbon-12 → Mass number = 12

• Carbon-14 → Mass number = 14

Important Points:

• Mass number is always a whole number

• It is different from atomic mass

• It helps determine the identity of isotopes

In conclusion, the mass number represents the total particles present in the nucleus and is important for understanding atomic structure and isotopes.