Atomic Structure — Question 7

(i) As Z has atomic number of 7, hence it has 7 protons. Electronic configuration of 2, 7 means the atom has 2 + 7 = 9 electrons. Therefore, element W has electronic configuration 2, 7 since its atomic number is 9.

(ii) Number of electron in X is 3. Therefore, electronic configuration = (2, 1). As X will try to lose 1 electron to attain stable state, hence, X has valency [1+]

Number of electron in Y is 8. Therefore, electronic configuration = (2, 6). As Y will try to gain 2 electrons to attain stable state, hence, Y has valency [2-]

Since valency of X is 1+ and valency of Y is 2-

Formula of the compound:

$\text{X}^{1+} \phantom{\nearrow} \text{Y}^{2-} \\[0.5em] \overset{\phantom{1}{1}}{\text{X}} \space {\searrow}\mathllap{\swarrow} \space \overset{2}{\text{Y}} \Rightarrow \underset{\phantom{2}{2}}{\text{X}} \space {\searrow}\mathllap{\swarrow} \space \underset{1}{\text{Y}} \\[0.5em]$

So, we get the formula as $\bold{X}_2\bold{Y}$