Each atom of protium has one
proton, no neutrons, and one electron. each
atom of deuterium has one proton, two
neutrons, and one electron. are these the
ame or different elements? why?

That depends on which hydrogen isotope you're referring to.

Hydrogen has three naturally occuring isotopes, protium, deuterium, and tritium.

Explanation:

Isotpes are elemens that have the same number of protons and electrons, but different numbers of neutrons.

So, an isotope of hydrogen will always have one proton in the nucleus and one electron surrounding the nucleus.

As you can see in the image, each of those three naturally occuring isotopes has a different number of neutrons in the nucleus.

Protium, which is usually called hydrogen, has one proton, one neutron, and one electron;

Deuterium has one proton, two neutrons, and one electron;

Tritium has one proton, three neutrons, and one electron.

An atom's valence shell is simply the outermost energy level that is occupied by electrons. For all three hydrogen isotopes, the valence shell, which is the only shell occupied, will contain one electron.