The rule of 8!

Let us take a look at the Periodic Table once again.

Look at helium and neon

In the periodic table the elements found in the 18th or 0 group are in the gaseous form, under normal temperature and pressure conditions. They are called Noble or Inert Gases. Why are these gases given this name? We shall see the reason as we read further.

Helium is a Noble gas and neon is also a Noble gas.

In the atom factory, you have also made the helium atom.
 

The helium atom has only two electrons and both of these fill up in the first shell (energy level). The capacity of the first shell is also actually that of only two electrons.

You have also made the Neon atom.

Neon has a total of ten electrons. Out of these, two fill up the first energy level which has a capacity of two only and the remaining eight completely fill up the second energy level which has a total capacity of eight electrons.

Take a look at the atoms of the other Noble gases shown below. Also observe the number of electrons in the outermost shell.

In these too, you will find the number of electrons is - eight!

We find these gases naturally in their atomic form: Helium - in the form of helium atom, Neon - in the form of neon atom.

In nature, it is very rare to find these elements combined with some other element in the form of a compound.
 

They do not combine with any other element. If you specially try to combine these gases with some other element in a laboratory, it is still not easy to do so.

With these learnings in mind, scientists came to the conclusion that if the outermost shell of an atom is full, the atom/element is inert and it is not easy to make it react with any other element. This is also known as the Octet Rule, since all inert gases, except helium, require eight electrons in the outermost shell for it to be full.

The outermost shell requires eight electrons for the shell to be full. This is called the Octet Rule.

Is there any link between the total number of electrons in the outermost shell and the chemical reactivity of the element?