The atomic number of the elements X and Y are 20,26 respectively. When these elements combine with chlorine, three compounds XCl2,YCl2,YCl3 are formed. Explain the reason for this, on the basis of the subshell based electronic configuration.
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Solution
X20=1s2,2s2,2p6,3p6,4s2
X26=1s2,2s2,2p6,3s2,3p6,4s2,3d6
Y is a transitional element, In chemical reactions, only two electrons in ′s′ subshell or besides ′s′ subshell electrons ′d′ subshell electrons also take part.
The element X is calcium-20Ca−1s2,2s2,2p6,3s2,3p6,4s2
The element Y is iron-26Fe−1s2,2s2,2p6,3s2,3p6,4s2,3d6
Calcium can lose only two electrons and form CaCl2 But, due to the d−shell present in Fe, when it forms FeCl2, the configuration of d−shell in FeCl2 is d6. When it again loses an electron to form FeCl3 it forms a stable half-filled d5 configuration. That's why Fe has a variable oxidation state