In Chemistry (Class 9), Valency is defined as the combining capacity of an element. It tells us how many electrons an atom needs to lose, gain, or share to become stable (to complete its outermost shell / Octet).
Valency: The combining capacity of an element.
Valence Electrons: Electrons present in the outermost shell.
Rule for 1 to 4 valence electrons: Valency = Number of valence electrons.
Rule for 5 to 7 valence electrons: Valency = 8 minus the number of valence electrons.
Noble Gases: Valency is 0.
First, you must know the Atomic Number (Z) of the element. The atomic number equals the number of electrons in a neutral atom. Example: Oxygen has an atomic number of 8.
Distribute the electrons into shells (K, L, M, N) using the 2, 8, 8, 18 rule. Example for Oxygen (8 electrons): K-shell takes 2, L-shell takes 6. Configuration = 2, 6.
The electrons in the outermost shell are called Valence Electrons. Example: Oxygen has 6 valence electrons.
To become stable, an atom wants 8 electrons in its outermost shell (Octet rule).
Example Calculation for Oxygen: Since Oxygen has 6 valence electrons (which is greater than 4), we use Rule 2. Valency = 8 - 6 = 2. Oxygen needs 2 electrons to complete its octet, so its valency is 2.
First, write the electronic configuration to find the number of valence electrons (outermost shell). If there are 1 to 4 valence electrons, the valency is that exact number. If there are 5, 6, or 7 valence electrons, subtract that number from 8 to get the valency.
Sodium's configuration is 2, 8, 1. Since it has 1 valence electron, its valency is 1. It will lose 1 electron to become stable.
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