Classification of Elements and Periodicity in Properties

Valency, Oxidation states and Chemical reactivity

Oxidation State / Oxidation Number :
The amount of charge appears to be gained by an atom in a molecule is called oxidation state.
ex : O-2, F-, N-3, S-2 -----

Inert pair effect :
s- orbitals behave like inert gas because it is strongly attracted by nucleus cause poor shielding
→ Thallium = 6s2 6p1
Tl+ = stable
Down the group, oxidation state decreases so more stable.
Pb+2 > Pb+4 (stability)

Diagonal relationship :

element of a group in 2nd period resembles in its properties.

Reasons for diagonal relationship :
→ Nearly same atomic and ionic size
→ Nearly same electronegativity
→ Nearly same polarising power.
\tt Polarising \ power = \frac{Ionic \ character}{(Ionic \ radius)^{2}}
Be and Al are amphoteric.

Part1: View the Topic in this Video from 0:11 to 11:03

Part2: View the Topic in this Video from 0:12 to 11:52

Part3: View the Topic in this Video from 0:16 to 6:37

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