Number of elementary particles in an atom

[i.physics]

How Number of elementary particles in an atom are counted?

 

[Bystander]

What particles are you counting?

 

[mfb]

"Number of elementary particles" is not a well-defined quantity, especially for the nucleus.
You can count electrons (elementary), protons and neutrons (not elementary), but trying to count the elementary quarks, photons or gluons doesn't give a meaningful result.

 

[i.physics]

Say number of electrons and protons. We have been taught hydrogen has 1 proton and electron each which forms an hydrogen atom. My Q is how these particles numbers were counted?

 

[Nugatory]

Say number of electrons and protons. We have been taught hydrogen has 1 proton and electron each which forms an hydrogen atom. My Q is how these particles numbers were counted?

For most of the common stuff:
The mass of the atom tells us the number of neutrons plus the number of protons (google for "atomic mass").
The chemical properties of the atom tell us the number of electrons (google for "periodic table").
We know that the number of protons must be equal to the number of electrons.

That's enough information to determine the number of protons, the number of neutrons, and the number of electrons.

Be aware, however, that it all looks a lot easier in hindsight... We're talking about several centuries of hard work, with each new development built on the previous one, to produce the neat tables that we see today.