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Trends in Atomic Properties & Physical Properties
Question

A, B, C, D and E(Francium is not included in the list) are the elements belonging to First group of Modern periodic table. The Electronegativity trend of these elements is  A > B > C = D > E. The element ‘E’ in the sequence is

Moderate
Solution

A) Atomic radius…Li<Na<K<Rb<Cs;

B)IP1…..Li>Na>K>Rb>Cs;

C) EN…..Li>Na>K=Rb>Cs;

D) MP…Li>Na>K>Rb>Cs;

E) BP…Li>Na>K>Rb>Cs;

F) Hardness, Metallic bond strength….Li>Na>K>Rb>Cs;

G) Metallic character….Li<Na<K<Rb<Cs;

H) Density…..Li<K<Na<Rb<Cs;

     Due larger inter atomic distances available vacant orbitals Potassium is less denser than Sodium.

I) Abundance in Earth's crust….Na>K>Rb>Li>Cs;

J) Hydration Enthalpy….Li+>Na+>K+>Rb+>Cs+

Thus ionic size in aqueous solution…..Li+>Na+>K+>Rb+>Cs+

Thus ionic mobility in aqueous solution…..Li+<Na+<K+<Rb+<Cs+ 

but ionic mobility in fused state ……Li+>Na+>K+>Rb+>Cs+

K) EM+/M° values are negative.

Most negative for Li and least negative for Na.

ELi+/Li°most negative<ECs+/Cs°<ERb+/Rb°<EK+/K°<ENa+/Na°least negative

Best reducing agent is Lithium, best oxidant is Na+;

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