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Why hydrogen have only one atomic number?
Answer 1:

That is an interesting question. The atomic number of an atom is the number of protons that atom has. Almost every atom is made of three different things: protons, neutrons, and electrons. Protons and neutrons are in the middle of an atom and form what is called a nucleus. Electrons surround the nucleus. A nucleus and its electrons make up an atom. The nucleus is very small compared to the space of the whole atom. If the nucleus were an apple, the whole atom (the nucleus and electrons) would be the size of a football stadium!

A hydrogen atom is made of one proton and one electron. Because hydrogen has one proton, it has an atomic number of one. It is the only element whose atoms don't have any neutrons. Helium has an atomic number of two; helium has two protons, two neutrons, and two electrons.

Why does hydrogen have only one proton? It may be because hydrogen was one of the first elements to exist in the universe. About 700 million years after the Big Bang, things like protons, neutrons, and electrons began to come together to form atoms. It was around this time that hydrogen happened. Because hydrogen has been around for so long, there is more of it in the universe than any other element. Scientists think that about 75% of the universe's mass is just hydrogen!

Answer 2:

Hydrogen has atomic number of 1 because it has only one particle in the nucleus. It is the lightest element, with only a single proton, which gives it an atomic number of 1.

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