s-BLOCK ELEMENTS

S.No. Atomic Properties Alkali metal 1. Outer electronic configuration ns^1 2. Oxidation number and valency (i) These elements easily form univalent +ve ion by losing loosely solitary ns^1 electron due to low IP value. 3. Atomic and Ionic radii Increases down the group, because value of n ( principal quantum number ) increases. Order = Li < Na < K < Rb < Cs. 4. Ionisation Energy As size increases, I.E. decreases down the group ( so Cs have lowest I.P. ) Order = Li > Na > K > Rb > Cs 5. Electropositive character or metallic character Alkali metals are strongly electropositive and metallic. Down the group electropositive nature increase so metallic nature also increases. I.E. M ---> M^+ + e^- Metallic Nature : Electropositive character § 1/ I.P. Order = LiNa>K>Rb>Cs