WHY DO ATOMS FORM CHEMICAL BONDS?

 It is a universal rule that everything in this world tends to become more stable.  Atoms achieve stability by attaining electronic configuration of noble gases (He, Ne or Ar, etc ) i.e. ns^2  np^6. Having 2 or 8 electrons in the valence shell is a sign of stability.

DEFINITIONS:

 

 Attaining two electrons in a valence shell is called duplet rule while attaining eight electrons in valence shell is called the octet rule.

               The noble gases do have 2 or 8 electrons in their valence shells. It means that all noble gases have their valence shells completely filled. Their atoms do not have vacant space in their valence shell to accommodate extra electrons. Therefore, noble gases do not gain, lose, or share electrons. That is why they are non-reactive.

     The importance of the noble gas electronic configuration lies in the fact that all other atoms try their best to have the noble gas electronic configuration. For this purpose, atoms combine with one another, which is called chemical bonding. In other words, atoms form chemical bonds to achieve stability by acquiring an inert gas electron configuration.

  Methods of Accommodation of Electrons in valence shells:

  An atom can accommodate 8 electrons  in its valence shell in three ways:

1.     By giving valence shell electrons (if they are less than three) to other atoms.

2.     By gaining valence shell electrons from other atoms (if the valence shell has five or more electrons in it).

3.     By sharing valence electrons with other atoms.

                              It means every atom has a natural tendency to have 2 or 8 electrons in its valence shell. The atoms having less than 2 or 8 electrons in their valence shell are called unstable.

                                                         Now the question arises how can we identify the way an atom reacts? The position of an atom in the periodic table indicates its group number. The number of groups is assigned on the basis of valence shell electrons. For example, group 1 has 1 electron in its valence shell, group 2 has 2 electrons in its valence shell and group 17 has 7 electrons in its valence shell. The mode of the reaction of an atom depends upon its number of valence shell electrons. It is discussed in the next sections.

 Chemical Bond:

                                        A chemical bond is defined as a force of attraction between atoms that holds them together in a structure. In other words, during bond formation, there is some force which holds the atoms together.

This attaining of 8 electrons configuration I the outermost shell either by sharing, losing or by gaining electrons is called the octet rule. This octet rule only symbolizes that noble gas electronic configuration should be attained by atoms when they combine or react. For elements like hydrogen or helium; which have only s-subshell, becomes duplet rule . It plays a significant role in understanding the formation of chemical bonds between atoms.

                           If the bond the formation is between ions, it is due to an electrostatic force of attraction between them. But if bond formation is between similar atoms or between the atoms that have to compare able electronegativities, then the chemical bond formation is by ‘sharing’ of electrons. This sharing of electrons may be mutual or one-sided.

                          When two approaching atoms come closer, the attractive, as well as repulsive forces, become operative. The formation of a chemical bond is a result of net attractive forces that dominate. The energy of that system is lowered and the molecule is formed. Otherwise, if repulsive forces become dominant no chemical bond will be formed. In that case, there will be an increase in the energy of the system due to the creation of repulsive forces.