Question

Explain briefly how +2 state becomes more and more stable in the first half of the first row transition elements with increasing atomic number?

Answer 1

The oxidation states displayed by the first half of the first row of transition metals are given in the table below

Oxidation state	Sc	Ti	V	Cr	Mn
		+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 4selectrons by these metals. Since the number of delectrons 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 d 5electrons (that is half-filled dshell, which is highly stable).