How do the structure of the atoms of Hydrogen and Helium differ?
The structures differ in the number of protons, neutrons and electrons.
Hydrogen has only one proton and most commonly has no neutrons.
Helium has two protons and needs to have at least two neutrons to provide stability and hold the positively charged protons together.
( With only one proton in Hydrogen there is no positive to positive repulsion and so no need of neutrons.)
Hydrogen has only 1 electron in the 1 s energy shell
This means that Hydrogen is not stable as a single atom. Hydrogen must join with another Hydrogen
Helium has 2 electrons in the 1 s energy shell
This means the Helium is stable as a single atom and does not join with another Helium or other atoms.