First slide

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 Metallic radius trend of these elements is A > B > C > D > E. The element ‘B’ in the sequence is

Moderate

A

K
B

Na
C

Cs
D

Rb

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) $E_{M^{+} / M}^{°}$ values are negative.
Most negative for Li and least negative for Na.
$E_{{Li}^{+} / Li}^{°} (most negative) < E_{{Cs}^{+} / Cs}^{°} < E_{{Rb}^{+} / Rb}^{°} < E_{K^{+} / K}^{°} < E_{{Na}^{+} / Na}^{°} (least negative)$
Best reducing agent is Lithium, best oxidant is Na⁺;

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