NEET-XII-Chemistry
08: The d-and f-Block Elements
- #3Explain briefly how +2 state becomes more and more stable in the first half
of the first row transition elements with increasing atomic number?
Ans : The oxidation states displayed by the first half of the first row of transition metals are given in the table below.
-
Sc Ti V Cr Mn Oxidation state
+ 2 + 2 + 2 + 2 +3 + 3 + 3 + 3 + 3 + 4 + 4 + 4 + 4 + 5 + 5 + 6 + 6 + 7
It can be easily observed that except Sc, all others metals display +2 oxidation state. Also, on moving from Sc to Mn, the atomic number increases from 21 to 25. This means the number of electrons in the 3d-orbital also increases from 1 to 5.
-
Sc (+2) = d1 Ti (+2) = d2 V (+2) = d3 Cr (+2) = d4 Mn (+2) = d5
+2 oxidation state is attained by the loss of the two 4s electrons by these metals. Since the number of d electrons in (+2) state also increases from Ti(+2) to Mn(+ 2), the stability of +2 state increases (as d-orbital is becoming more and more half-filled). Mn (+2) has d5 electrons (that is half-filled d shell, which is highly stable).
-