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## ATOMIC NUMBER AND MASS NUMBER

Atomic Number

Definition of Atomic Number: Atomic number of an element is the number of protons present in the nucleus of an atom. For example,

Atomic Number of Carbon: There are 6 protons present in the nucleus of carbon atom so the atomic number of carbon element is 6. The atomic number of an element is always represented by letter Z. thus,

Atomic Number (Z) = No. of protons

Mass Number

Definition of Mass Number: Mass number of an element is the total number of protons and neutrons present in the nucleus of an atom. For example,

Mass Number of Carbon: There are present 6 protons and 6 neutrons in the nucleus of carbon atom, so mass number of carbon element is 12. The mass number of an element is always represented by letter A. thus,

Mass Number (A) = No. of protons + No. of neutrons

To see periodic table with mass number click here

Representation of Atomic Symbol of an Element Representation of Atomic Symbol of Carbon Calculation of number of neutrons from mass number and atomic number

The number of neutrons present in the nucleus of an atom can be calculated from the known values of mass number and atomic number of that element using following expression:

Number of neutrons = mass number – atomic number

Or number of neutrons = A – Z

For example, the number of neutrons in carbon can be found by using this formula. Carbon has mass number 12 and atomic number 6. By subtracting these values from each other we get the number of neutrons in carbon.

Number of neutrons in carbon = mass number of carbon – atomic number of carbon

Number of neutrons in carbon = 12 – 6

Number of neutrons in carbon = 6

Test Your Understanding and Answer These Questions:

1. What is mass number?

2. How to find mass number of an element?

3. Give atomic number definition.

4. Give mass number definition.

5. How to find the number of neutrons in an element?

Developers of Fun Science Rajan Gupta M.Sc, B.Ed. & LL.B. Teacher, Author & Innovator Rahul Jindal B.Tech Entrepreneur & Innovator 