Why are the inner planets made of denser materials than the outer planets?

The man reason to have inner part denser than outer part is sun gravity.The sun gravity try to pulls the high density  materials towards the inner part and due to this high density materials get accumulate at inner part but on the other hand lighter materials accumulated at the outer part.

At the inner part of the nebula there are high temperature so only rocks and metals were able to condense,but at the outer part hydrogen compounds ere only able to condense.