1. This document provides a 3-step technique for determining whether a spinel compound will be normal or inverse based on its chemical formula. It focuses on transition metal spinels commonly found in entrance exams. 2. Step 1 examines the metal cations, step 2 looks at the divalent cation if both are transition metals, and step 3 determines if a transition metal spinel is normal or inverse based on the trivalent cation. 3. The technique establishes general rules like period 3 p-block trivalent cations yielding normal spinels and period 4,5 p-block yielding inverse, and exceptions for certain transition metal combinations.

1. Most efficient and time saving
technique for SPINELS!
Focus: M.Sc Entrances (IIT-JAM, TIFR, JNCASR, Various
Universities), CSIR-NET, GATE, BARC, PSUs….
Myself Abhay, M.Sc from IIT Guwahati, Qualified
CSIR-JRF

2. SPINELS
 Spinel general formula:
AB2O4
{A(II)O}{B(III)
2O3}
A2+
B3+

3.  Step I.
Watch out if all metals are transition or non-transition.
 Among all the existing spinels, only the trivalent metal cation
or B3+ belongs to p-block.
If both transition metals, then proceed to step II else look below:
B3+ belongs to Period 3 Al...........NORMAL
MgAl2O4, NiAl2O4, MnAl2O4
B3+ belongs to Period 4,5 Ga, Sn ......INVERSE
ZnSn2O4, NiGa2O4, MnGa2O4, MgGa2O4

4.  Step II.
If both are transition metal ions, then look for divalent metal
cation A2+ .
 If A2+ is either Zn2+ or Mn2+
 Zn2+ or Mn2+ : Always NORMAL
E.g. ZnFe2O4, MnFe2O4 are always Normal
 Other than these : Check B3+ in step III.

5.  Step III.
 If both ions belong to Transition metal series then
 Only those having
Will be INVERSE!
 E.g., Fe3O4, NiFe2O4, MgFe2O4
 Only exception to ZnFe2O4 and MnFe2O4.
Fe3
+

6. Summary:
1
• P-block B3+ : Period 3; Al; Normal
• P-block B3+ : Period 4,5; Ga, Sn; Inverse
2
• D-block B3+
• A2+; Zn or Mn; always NORMAL
3
• Both metals belong to d block
• Fe3+ INVERSE
• Remember Zn or Mn