Physical Properties - Electron Gain Enthalpy

Which of the following statements are correct?

(i) Helium has the highest first ionisation enthalpy in the periodic table.

(ii) Chlorine has less negative electron gain enthalpy than fluorine.

(iii) Mercury and bromine are liquids at room temperature.

(iv) In any period, atomic radius of alkali metal is the highest.

Match the correct ionisation enthalpies and electron gain enthalpies of the following elements.

Among halogens, the correct order of amount of energy released in electron gain (electron gain enthalpy) is ______.

Which of the following pair of elements would have a more negative electron gain enthalpy?

F or Cl

The formation of the oxide ion, \[\ce{O2- (g)}\], from oxygen atom requires first an exothermic and then an endothermic step as shown below:

\[\ce{O (g) + e- -> O- (g) ; ∆H^Θ = - 14 kJ mol^{-1}}\]

\[\ce{O- (g) + e- -> O^{2-} (g) ; ∆H^Θ = + 780 kJ mol^{-1}}\]

Thus process of formation of \[\ce{O^{2-}}\] in gas phase is unfavourable even though \[\ce{O^{2-}}\] is isoelectronic with neon. It is due to the fact that,

Which of the following pair of elements would have a more negative electron gain enthalpy?

O or F

Describe the theory associated with the radius of an atom as it gains an electron.

Assertion: The most electronegative element in the periodic table is F.

Reason: Fluorine has the highest negative electron gain enthalpy.