Question

Caesium, ${\text{Cs}}$, is an element in Group I of the Periodic Table. When Caesium reacts, it forms a positive ion, $C{s^ + }$. How is a caesium ion formed?
(a) A caesium atom gains a proton
(b) A caesium atom gains an electron
(c) A caesium atom loses an electron
(d) A caesium atom shares an electron

Answer 1

Group I elements are electropositive elements which means that they will from carbocations only and not carbanion to make itself stable according to octet rule.

Complete step by step answer:
An atom in the ground state has an equal number of protons and electrons. The number of protons in an atom is fixed. So, atoms can only gain, lose or share electron(s). When an atom gains an electron, it forms a negative ion known as carbanion and when an atom loses an electron, it forms a positive ion called carbocation. Group $1$ elements have the property of Electro positivity, which is the tendency to lose electrons, and form positive ions. Caesium is a Group $1$ element having electronic configuration as ${\left[ {Xe} \right]_{54}}6{s^1}$ so, it has only one electron in the outermost shell. So, it will lose one electron to form $C{s^ + }$ ion and attain the stable configuration of the nearest gas Xenon by the Octet rule, which says, elements with $8$ electrons in the outermost shell are more stable.
Option (a) is incorrect because gaining a proton is not possible, since the number of protons is fixed.
Option (b) is incorrect because gaining an electron would make $C{s^ - }$ ,which is not seen in Group I elements.
Option (c) is the correct answer as discussed; Caesium can form $C{s^ + }$ ion only by losing an election.
Option (d) is incorrect because Group I elements do not form covalent bonds by sharing electrons.
Hence, option(c) is the only correct explanation of how Caesium ion, $C{s^ + }$ is formed.

So, the correct answer is Option C .

Note:
To take out an electron from an atom, the atom should be isolated, gaseous and neutral. Since, taking out an electron is an endothermic process, it requires some amount of energy to be given from outside called ionization energy.