Chapter 15, Problem 18RQ

To determine

The number of shells needed to explain the periodic table.

Answer to Problem 18RQ

The eight electrons in their outermost shell are needed for the atom to be stable according to octet rule.

Explanation of Solution

The electrons in the outermost shell decide the chemical properties of the atom. Each shell contains one or more sub-shells, and each sub-shell consists of one or more atomic orbital.

The number of shells in the atom is decided by the number of electrons present in the atom. The more number of electrons in an atom, more will be the number of shells filled by the electron in the atoms.

For example the carbon atom consists of six electrons and it has two shells that occupy these electrons. And in the magnesium atom, there are 12 electrons and three shells are needed to fulfill the octet rule in the atom, first shell contains two electrons, second shell contains 8 electrons, while third shell contains 2 electrons.

The most stable atoms have their outermost electron shell full. Most of the elements need eight electrons in their outermost shell in order to be stable.

Conclusion:

Therefore, the eight electrons in their outermost shell are needed for the atom to be stable according to octet rule.