An element X has 2 electrons in its M shell, it forms bond with an element Y which has 7 electrons in its third orbit. (a) Write the formula of the compound formed. (b) Which nearest inert gas electronic configuration will element X and Y acquire. (c) Show by orbital diagram the formation of compound between X and Y.

 Question:

An element X has 2 electrons in its M shell, it forms bond with an element Y which has 7 electrons in its third orbit.

 (a) Write the formula of the compound formed. 

(b) Which nearest inert gas electronic configuration will element X and Y acquire. 

(c) Show by orbital diagram the formation of compound between X and Y.

Solution:

(a)         XY₂

(b)         Element X will acquire the electronic configuration of Neon (2, 8), and element Y will acquire the electronic configuration of Argon (2, 8, 8).

(c)          Orbital diagram for the formation of compound between X, which is magnesium and Y, which is chlorine.

Explanation:

 M shell means third orbit as the shells are named as K, L , M, ...    

X has 2 electrons in its third shell, so its configuration will be 2, 8, 2.

Y has 7 electrons in its third shell, so its configuration will be 2, 8, 7.

(a) It is clear from their configuration that X will lose 2 electrons to have 8 electrons in its last shell, so its valency is 2. Y will gain 1 electron to have 8 electrons in its last shell, so its valency is 1.

Apply criss cross method, and the valencies will get exchanged so that the formula is XY₂. 

(b)  After losing 2 electrons, X will have the configuration 2, 8.

After gaining 1 electron, Y will have he configuration 2, 8, 8.