5 public questions tagged with this topic.
First ionization enthalpy decreases down a group due to increased atomic size and shielding. Among Li, Na, K, and Cs, Cs (period 6) has the lowest value.
Ref: NCERT Class 11 Chemistry > Chapter 3: Classification of Elements and Periodicity in Properties > Topic: Periodic Trends - Atomic Radii Ionic Radii and Ionization Enthalpy
Reactivity with water increases down group 1 due to decreasing ionization enthalpy. Cs (lowest ionization enthalpy) reacts most vigorously among Li, Na, K, and Cs.
Ref: NCERT Class 11 Chemistry > Chapter 3: Classification of Elements and Periodicity in Properties > Topic: Periodic Trends - Atomic Radii Ionic Radii and Ionization Enthalpy
Second ionization enthalpy for group 1 elements involves removing an electron from X+ (noble gas configuration). Cs⁺ (largest size) has the lowest value due to reduced nuclear attraction.
Ref: NCERT Class 11 Chemistry > Chapter 3: Classification of Elements and Periodicity in Properties > Topic: Periodic Trends - Atomic Radii Ionic Radii and Ionization Enthalpy
Group 1 elements (except Li) form oxides of the type X₂O. Rb, being in group 1, forms Rb₂O, unlike Mg, Al, or P.
Ref: NCERT Class 11 Chemistry > Chapter 3: Classification of Elements and Periodicity in Properties > Topic: Electronic Configuration and Types of Elements - s p d f Blocks
