"A chemical bond may be defined as the attractive force which holds together the constituent atoms of a chemical species."
Cause of chemical combination
1. Tendency to acquire noble gas configuration : Octet rule.The first logical explanation about the cause of chemical combination is based upon the study of electronic configuration of noble gases. The electronic configuration of these elements is given in table.
Fore the study of electronic configuration of these gases it is revealed that the s and p orbitals of the outermost shells are completely filled.(In case of helium,there is only one orbital i.e.,1s which is completely filled).The unusual stability of noble gases was linked with the s2p6 configuration (1s2 in case of helium) of the noble gases.
The electronic configuration of all the remaining elements do not have 8 electrons or s2p6 configuration all these elements are chemically reactive.The principal of acquiring 8 electrons in the valence shell is called octet rule.
Limitation of octet rule : The octet rule could explain the formation of a large number of molecules but failed to explain(i) the formation of molecules such as BF3 and AICI3 (Where the central atom has 6 electrons instead of 8 in their valance shell) and (ii) the formation of compounds such as PCI5 and SF6 (where the central atom has 10 or 12 electron instead of 8).Moreover,the basis of the development of octet rule was the chemical inertness of noble gases.However,it has now been well established that the noble gases (especially krypton and xenon)form many compound like krf2,xef4 and xef6. Therefore,a more rational explanation for the cause of chemical combination is based upon the energy concept.
2. Tendency to acquire minimum energy : When two atoms approach each other,two new forces of attraction and repulsion come into existence between their electrons and nuclei.The forces of attraction lead to the decrease in energy of the system and the forces of repulsion lead to increase in the energy of the system.If the attractive forces over power the repulsive forces,the energy of the system decreases and thus a chemical bond is formed.
Cause of chemical combination
1. Tendency to acquire noble gas configuration : Octet rule.The first logical explanation about the cause of chemical combination is based upon the study of electronic configuration of noble gases. The electronic configuration of these elements is given in table.
Fore the study of electronic configuration of these gases it is revealed that the s and p orbitals of the outermost shells are completely filled.(In case of helium,there is only one orbital i.e.,1s which is completely filled).The unusual stability of noble gases was linked with the s2p6 configuration (1s2 in case of helium) of the noble gases.
The electronic configuration of all the remaining elements do not have 8 electrons or s2p6 configuration all these elements are chemically reactive.The principal of acquiring 8 electrons in the valence shell is called octet rule.
Limitation of octet rule : The octet rule could explain the formation of a large number of molecules but failed to explain(i) the formation of molecules such as BF3 and AICI3 (Where the central atom has 6 electrons instead of 8 in their valance shell) and (ii) the formation of compounds such as PCI5 and SF6 (where the central atom has 10 or 12 electron instead of 8).Moreover,the basis of the development of octet rule was the chemical inertness of noble gases.However,it has now been well established that the noble gases (especially krypton and xenon)form many compound like krf2,xef4 and xef6. Therefore,a more rational explanation for the cause of chemical combination is based upon the energy concept.
2. Tendency to acquire minimum energy : When two atoms approach each other,two new forces of attraction and repulsion come into existence between their electrons and nuclei.The forces of attraction lead to the decrease in energy of the system and the forces of repulsion lead to increase in the energy of the system.If the attractive forces over power the repulsive forces,the energy of the system decreases and thus a chemical bond is formed.