Differing distances (temperatures) from the Sun allowed for the differing chemistries that would go into making the planets. The sequence in which the different materials condense out of the gas with temperature (or distance from the sun) is called the Condensation Sequence. Planets near by the sun were formed in much higher temperatures. The only materials that could condense out where the metals and silicates (Mercury, Venus, Earth and Mars). Very distant planets were formed in a much colder environment. These outer planets form from the condensation of water, ammonia and methane ices (Jupiter, Saturn, etc. and the distant comets).

The Formation of Protoplanets
Soon, the Solar nebula was made up mostly of fairly large (km size) planetesimals. They will have swept up most of the smaller grains nearby. Now, the solar system would be made up of millions of these irregular shaped, massive planetesimals.

In 100,000 years, planetesimals up to 10 km in size would have formed. The accretion continues, but fueled by the gravitational attraction of the biggest planetesimals: The big keep getting bigger swallowing up smaller planetesimals near its orbit. The ever growing planetesimal absorbs the mass and the orbital energy of all the smaller objects nearby, circularizing (averaging out) it's final orbit. Once all the smaller objects have been removed, the planetesimals themselves begin to collide! If they do so at high velocities, they will shatter. However, since most of the mass is going in the same direction around the Sun, their collisions are not at high differential velocities, and the mass is able to coalesce into still larger bodies.

Through collisions and accretion with each other, planetesimals grow to a much larger size. Now, perhaps a hundred Protoplanets form, with Moon masses (1/10th Earth). These mighty rocks, interfere with each other's orbits. This serves to slightly mix up the differing planet chemistries created based on distances from the Sun.

Most importantly, these protoplanets collide! This process creates the few final planets, when all protoplanets have been assimilated. The entire process of gas condensation to dust grains, accretion of dust grains to small rocks, collisions and coalescence into planetesimals, then proto-planets and then the final 9 planets took just 10 million yrs!