How do you explain the diagram that shows 4 energy levels of hydrogen - 1 at the bottom 4 at the top - the values are n4-0.85eV n3-1.51eV n2-3.4eV n1-13.6eV?

Answer 1

The diagram shows the ionization energies of hydrogen. The ionization energy for a ground-state electron in hydrogen is 13.6eV. Let's jump.

An electron orbits an atom of hydrogen in as low an energy level as possible. That's the ground state of hydrogen. To tear that electron away, it takes some amount of energy. In this case, it takes 13.6eV to strip off that electron. But what if the electron is in the next higher allowable energy level because the gas it hot? In that case, it takes less energy to tear that electron away because you've got a "head start" owing to the fact that the electron is in a higher orbital than the ground state. And what if it's in the next higher allowable energy level? Or the next? Less and less energy is required to strip off the electron as it moves to higher energy levels. These are the ionization energies of hydrogen.

These energy levels are specific to hydrogen. Each other element will have a different set if ionization energies associated with it. And with atoms with many electrons and complex electron structures, the problem can quickly become very complex.