Question

Considering the trends in ionization energies, would you expect sodium or potassium to be more reactive? Explain. Considering the trends in atomic radii, would you expect cesium or radon to have the larger radius? Explain. Compare the ionization energies of sodium and rubidium and then compare the electron affinities of chlorine and iodine. Which of the following chemical combinations of the elements would be the most exothermic - Na and Cl, Na and I, Rb and Cl, or Rb and I? Explain. Chlorine (Cl_2) is used extensively as a disinfectant and bleaching agent. Without regard to effects or costs, would bromine (Br_2) be a more or less effective disinfectant and bleaching agent? Explain. Is fluorine gas (F_2) predicted to be more or less reactive than chlorine gas (Cl_2)? Explain. Not much is known about the chemistry of astatine (At_2). Would you expect astatine to be more or less reactive than iodine (I_2)? Explain.

Answer 1

1. Part-A: Ionization energy decreases with increase in atomic radius. Since the atomic radius of potassium is more, it has less ionization energy. Hence it is easier to remove an electron from potassium. Hence potassium is more reactive.

2. Part-A: Caesium and Radon belong to same period. But there is only one valence electron in Cs, where the Valence shell of boble gas of Rn is completely filled and hance the later element has higher effective charge. Hence the atomic radius of Cs is more.

3. Part-A: Between Na and Rb, Na has higher ionization energy due to smaller radius. Between Cl and I, Cl has higher electron affinity.

The chemical reaction of Rb and Cl is the most exothermic. Because Rb has the lowest ionization energy and hence lesser energy is required to remove the electron. Cl has the highest electron affinity and hence highest energy is liberated when receives an electron. Hencewhen Rb combines with Cl highest energy is liberated.

4. Part-C: Br2 would be moreefficient as a bleaching agent and disinfectant due to smaller bond dissociation enthalpy of Br2 in comparison to Cl2.

5: Part-C: F2 is more reactive than Cl2. This is due to the smaller size and high electronegativity of F - atom, the repulsion between the two F - atom in F2 is more. Hence the bond dissociation enthalpy of F2 is less thaan Cl2. Due to lesser BDE, F2 is morereactive.