Inner planets are smaller, denser (about 5 times water's density), rotate relatively slowly, have rather heavy molecules in their atmosphere.
Outer planets are larger, relatively light (about water's density), and rotate rapidly (especially in view of their large sizes); both their interiors and their atmospheres are made up lighter elements.
Outer planets have many satellites, some of which are almost as
large as the Earth. Mercury and Venus have no satellites, the Earth one, and
Mars two (very small ones).