i. Actinoids have variable oxidation states ranging from +2 to +7 due to availability of 5f, 6d and 7s orbitals.
ii. The common oxidation state of actinoid elements is +3. +3 oxidation state is formed by loss of two 7s and one 5f or 6d electrons.
iii. With increase in atomic number, +3 oxidation state becomes more and more stable.
iv. Beside +3 oxidation state, actinoids show +2, +4, +5, +6 and +7 oxidation states.
a. Elements Am and Th show +2 oxidation state.
eg. ThI2, ThS, ThBr2, etc.
b. Elements Th, Pa, U, Np, Pu, Am and Cm show +4 oxidation state.
c. Elements Th, Pa, U, Np, Pu and Am also show +5 oxidation state.
d. Elements U, Np, Pu and Am show +6 oxidation state.
Note: When the oxidation number increases to +6, the actinoid ions form oxygenated ions due to high charge density.
eg. UO22+, NpO22+ , etc.
e. Np and Pu show +7 oxidation states.
v. Actinoids exhibit large number of variable oxidation states because all the electrons in 5f, 6d and 7s orbitals can take part in bond formation due to very small energy gap between these orbitals.
vi. Actinoids have more compounds in +3 oxidation state than in +4 oxidation state. However, compounds of actinoids in +3 and +4 oxidation states have tendency to undergo hydrolysis.
Note: Oxidation states of actinium and actinoids:
Ac |
Th |
Pa |
U |
Np |
Pu |
Am |
Cm |
Bk |
Cf |
Es |
Fm |
Md |
No |
Lr |
+2 |
+2 |
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+2 |
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+3 |
+3 |
+3 |
+3 |
+3 |
+3 |
+3 |
+3 |
+3 |
+3 |
+3 |
+3 |
+3 |
+3 |
+3 |
+4 |
+4 |
+4 |
+4 |
+4 |
+4 |
+4 |
+4 |
+4 |
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+5 |
+5 |
+5 |
+5 |
+5 |
+5 |
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+6 |
+6 |
+6 |
+6 |
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+7 |
+7 |
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