Question

Which of the following reactions requires more energy?
(A) $Cs(g)\to C{{s}^{+}}(g)+{{e}^{-}}$
(B) $C{{l}^{-}}(g)\to Cl(g)+{{e}^{-}}$
(C) ${{F}^{-}}(g)\to F(g)+{{e}^{-}}$
(D) $M{{g}^{-}}(g)\to Mg(g)+{{e}^{-}}$

Answer 1

Hint: According to the modern periodic table, the elements are arranged based on their order of increasing atomic number and periodic properties of elements. The periodic properties are in terms of ionization energy, electron affinity, atomic radius, electronegativity, and ionic radius. To predict the element’s physical, chemical, and atomic properties by using periodic law and table formation.

Complete step by step solution:
The minimum energy required to remove one electron from a neutral gaseous atom in its ground state to form a gaseous ion is called ionization energy or ionization enthalpy.
$X(g)\to {{X}^{+}}(g)+{{e}^{-}}$
The energy required for removing one electron is called first ionization potential and smaller ionization enthalpy which is easier to convert an atom into its positive ion.
(A) $Cs(g)\to C{{s}^{+}}(g)+{{e}^{-}}$
In this reaction, the amount of energy required removing one electron from a neutral gaseous cesium atom, and the energy is called ionization energy. From the shielding effect by electrons, Cesium exhibits lower ionization energy than other elements in the periodic table.
(B) $C{{l}^{-}}(g)\to Cl(g)+{{e}^{-}}$
(C) ${{F}^{-}}(g)\to F(g)+{{e}^{-}}$
From the above two reactions, the energy required for removing an electron from ${{F}^{-}}$ greater than $C{{l}^{-}}$ , because the outermost electron in chlorine is farther from the nucleus than the outermost electron in fluorine. Hence, ${{F}^{-}}$ has larger ionization energy means it requires more energy than $C{{l}^{-}}$ .
(D) $M{{g}^{-}}(g)\to Mg(g)+{{e}^{-}}$
Mg is an electropositive element which is not possible to form a negative ion.

Hence, the reaction C requires more energy than all the above reactions.

Note: Variation of ionization enthalpy in the periodic table decreases in the group when the atomic number increases. In periods, ionization enthalpy increases with the atomic number from left to right. When the elements with half or filled electronic configuration have more ionization enthalpy.