CBSE Class 9 Answered
(1) Electronic Configuration
The arrangement of electrons of each element is called the electronic configuration of the element.
(2) Valency
The valency of an element is defined as the number of electrons lost, gained or shared by its atom during a chemical combination.
(3) Valence Shell
The outermost shell or orbit of an atom is known as the valence shell or valence orbit.
(4) Valence Electrons
The electrons present in the outermost valence shell of an atom are called valence electrons.
(5) Noble Gases
The gases which have a stable octet and have little chemical reactivity are known as noble gases.
Example: In the helium atom, the outermost shell i.e. K shell has 2 electrons. Thus, it is completely filled.
Similarly, the gases neon, argon, krypton, xenon and radon have eight electrons in their outermost orbit