Question

An element X combines with oxygen to form an oxide ${{X}_{2}}O$. This oxide is electrically conducting.
(i) How many electrons would be there in the outermost shell of elements X
(ii) To which group of the periodic table does the element X belong.
(iii) Write the formula of the compound which is formed when X reacts with chlorine.

Answer 1

Write the electronic configuration of oxygen to find out its valency. Keep in mind that 2 atoms of X react with 1 atom of oxygen. So, the valency of X is half the total valency of oxygen excluding the polarity and considering only magnitude of valency. In accordance to that write the reaction between X and chlorine atom.

Complete step-by-step answer:
(i) As suggested in the hint we will write the electronic configuration of oxygen in its ground state.
E.C = $1{{s}^{2}}2{{s}^{2}}2{{p}^{4}}$
The valency of oxygen atom thus becomes 2.
Since two atoms of element X react with 1 oxygen atom, the valency of X is half of the valency of oxygen i.e. 1.
(ii) Since the element X has only electrons in its valence shell, the element belongs to group 1 of the periodic table i.e. the alkali metals.
(iii) Element X releases 1 electron per atom. On the other hand, chlorine atoms need 1 electron to form stable ions. So, the formula of compound formed when X reacts with chlorine is $XCl$.

Note: It is important to note that the valency of group 17 elements is also 1. However, since oxygen forms anion, elements X must form a cation for the compound ${{X}_{2}}O$ to exist. This is the reason why element X belongs to group 1 of the periodic table and not group 17.