Isotopes are atoms of the same element that have different numbers of neutrons.
The first shell can hold up to 2 electrons, the second shell can hold up to 8 (2 + 6) electrons, the third shell can hold up to 18 (2 + 6 + 10) and so on.
Explanation:
Since scientists think planets and meteorites were made at the same time and in the same place, it seems logical that whatever a meteorite is made of is also what planets are made of.
