In what ways are the inner planets different from the outer planets?
All planets were formed nearly 4.5 Billion years ago from a rotating, spherical cloud of diffused gas. This cloud then collapsed mainly due to a gravitational effect of a nearby event such as a dying star to give rise to our Sun. In the beginning the Sun was very Luminous and radiant. It managed to drive away almost all of the gas from the inner solar system, leaving only the rocky cores. But the Sun was not radiant enough to drive away this gas from the outer planets, and so with the passage of time, as the gas was already present in the outer solar system, these rocky cores managed to accrete mantles of gas, that is why outer planets are made almost entirely of gases mostly Hydrogen and Helium.
The inner planets due to their proximity to the sun have higher temperatures than the outer planets, also their rotation period is smaller compared to the outer planets.