What is the composition of our sun and its planets/moons and why is that composition so different?

Our solar system was formed from a “cloud of gas”, mainly hydrogen and helium. Why is the composition of our solar system so different and why, in contrast to the sun, do we find much less hydrogen and helium on earth, but all other substances? Furthermore, why did the inner planets become hard and the outer ones remain gaseous (eg Jupiter)? And their moons & Pluto are hard again? How about all that?

Thanks in advance.