The nucleus of an atom is made up of protons and neutrons. The atomic number of an element is the total number of protons it contains. The mass number is the total number of protons and neutrons that it contains. So subtracting the atomic number from the mass number is how you can determine the number or neutrons in an element. For carbon, the atomic number is 6 and the mass number is 12, so the number of neutrons is 12-6=6. In actuality, all elements are found in nature with varying numbers of neutrons in their nuclei. These compounds that differ only by the number of neutrons in their nuclei are called isotopes. For example, carbon-12 is the example that I mentioned above. But carbon-13 has 13-6=7 neutrons and the two are isotopes of each other (different isotopes of carbon).

Suppose you have the periodic table cell. Example for oxygen, 16 is at the top, O in the middle and 8 at the bottom. Okay? I hope you got that. Now 16 is the proton number + neutron number and 8 is the neutron number. So, you subtract 8 from 16, 16 - 8 = 8, Therefore, 8 is the proton number.

Cheers!

**proton number= electron number= atomic number****atomic mass of an element is proton number + neutron number.**- so for getting neutron number u have to
**subtract proton number from atomic mass.** - eg: atomic mass of
**sodium is 23** - atomic number of sodium ( proton number / electron number)
**is 11** -
**no. of neutrons**=**23- 11= 12.** - eg: atomic mass of
**Carbon is 12** - atomic number
**= 6** **no. of neutrons = 12- 6 = 6.**

hope u got it.....