The answer to this question is hidden in the electronic configurations of the noble gases. It was found that noble gases namely helium, neon, argon, krypton, xenon and radon did not react with other elements to form compounds, i.e. they were non-reactive. Earlier they were also called as inert gases. It was, thus, thought that these noble gases lacked reactivity because they had electronic arrangements which were quite stable. When we write the electronic configurations of the noble gases (see table 5.1 below), we find that except helium all of them have 8 electrons in their outermost shell.

Electronic configuration of Noble gases

Name	Symbol	Atomic number	Electronic configuration	No. of electrons in the outermost shell
Helium	He	2	2	2
Neon	Ne	10	2,8	8
Argon	Ar	18	2,8,8	8
Krypton	Kr	36	2,8,18,8	8
Xenon	Xe	54	2,8,18,18,8	8
Radon	Ra	86	2,8,18,32,18,8	8

Thus, it was concluded that atoms having 8 electrons in their outermost shell are very stable and they did not form compounds. It was also observed that other atoms such as hydrogen, sodium, chlorine etc. which do not have 8 electrons in their outermost shell undergo chemical reactions. They can stabilize by combining with each other and attaining the above configurations of noble gasses, i.e. 8 electrons (or 2 electrons in case of helium) in their outermost shells. Thus, atoms tend to attain a configuration in which they have 8 electrons in their outermost shells. This is called the octet rule. The octet rule explains the chemical bonding in many compounds.
Atoms are held together in compounds by the forces of attraction which are called chemical bonds. The formation of chemical bonds results in the lowering of energy, i.e. as compared to the individual atoms the resulting compound is lower in energy and hence is more stable. Thus stability of the compound formed is an important factor in the formation of chemical bonds. In rest of the lesson; you will study about the nature of bonds present in various substances. We would explain ionic bonding and covalent bonding in detail while briefly touch upon the bonding in metals and hydrogen bonding. Before you start learning about ionic bonding in the next section, you can answer the following questions to check your understanding.