Question

Question: Huge tables of characteristic X-rays start at lithium. Why not hydrogen or helium?

Short answer

Answer

X-rays do not start at hydrogen or helium because all of the electrons are n= 1 electrons.

Step-by-step solution

Definition of electron configuration

In atomic physicsandquantum chemistry, the electron configuration is the distribution ofelectronsof anatomormolecule(or other physical structure) inatomicormolecular orbitals.

Calculate electronic configuration for hydrogen and helium

Given that the atomic number of hydrogen is Z (H) =1

The atomic number of helium is Z (He) =2

The electron configuration for hydrogen is 1s¹

The electron configuration for helium is 1s²

Determine the reason

As we see, all of the electrons of hydrogen/helium are on the n = 1 level and this is the only level (shell) present. In order for the X-rays to be created, there must be a hole where an upper electron will fall which is not the case for hydrogen and helium.

Therefore X-rays do not start at hydrogen or helium because all of the electrons are n= 1 electrons.