Describe the differences in the atomic structures of a hydrogen atom and a helium atom.
i need a paragraph, i will give you lots of : -)

The other answer here says nothing about the structures
of a Hydrogen atom or a Helium atom.

In "classical terms" ... where we picture an atom something
like a tiny tiny solar system ...

-- The nucleus of a Hydrogen atom is a single proton,
whereas the nucleus of a Helium atom is a tightly bound
bundle of four particles ... 2 protons and 2 neutrons. 
This also means that every atom of Helium has 4 times
the mass of a Hydrogen atom.

-- In addition to the atomic nucleus, one electrically-neutral
atom of Hydrogen has an electron associated with the nucleus
and at some distance from it, whereas an electrically-neutral atom
of Helium has two electrons.