Actinides- Occurance-Electronic configuration - oxidation states- Actinide contraction - colour of the actinide cations- formation of complexs- comparison

1. Dr.P.GOVINDARAJ
Associate Professor & Head , Department of Chemistry
SAIVA BHANU KSHATRIYA COLLEGE
ARUPPUKOTTAI - 626101
Virudhunagar District, Tamil Nadu, India

2. Definition
A group of 14 elements after Actinium (z = 89) from Thorium (z = 90) to
Lawrencium (z = 103) in the periodic table having the general electronic
configuration: 5f1-146d0−27s2 including Actinium are called Actinides

3. Electronic configuration of Actinides
• The complete and valence shell
electronic configuration of the actinides
in their ground state are shown in the
table
• The table shows that 5f and 6d orbitals
in the actinides are partially-filled while
7s orbitals is completely-filled
• By the addition of electron, one by one,
to 5f orbital resulted from thorium to
lawrencium.

4. General characteristics of Actinides
1. Occurrence
• The Actinides like Actinium (Ac), Thorium (Th), Protactinium (Pa) and
Uranium (U) are occurring in nature as uranium minerals
Examples: Monazite sand and Thorite
• The remaining actinides are unstable and made artificially by nuclear
transmutations
• The actinide elements lying beyond uranium (z = 92), i.e., the actinide
elements with atomic numbers 93 to 103 are called trans-uranium elements

5. 2. Oxidation state
• The important oxidation states shown by actinides
are given in the table
• For Th, Pa and U, the most stable oxidation states are
+4, +5 and +6 respectively showing that all the outer
electrons are used for bonding
• For Np and Pu, the most stable oxidation states are +5
and +4
• In Am, Cm, Bk, Cf, Es, Fm, Md and Lr, the most stable
oxidation state is +3 in each case
• In No the most stable oxidation state is +2 since it
corresponds to 5f14 (completely filled) configuration
• In Am and Bk, the moderately stable oxidation states are
+2 and +4 respectively and these are on account of their
5f7 (half filled) arrangement.
Element Symbol Oxidation
states
Actinium Ac +3
Thorium Th +3,+4
Protactinium Pa +3,+4,+5
Uranium U +3,+4,+5,+6
Neptunium Np +3,+4,+5,+6,+7
Plutonium Pu +3,+4,+5,+6,+7
Americium Am +2,+3,+4,+5,+6
Curium Cm +3,+4
Berkelium Bk +3,+4
Californium Cf +2,+3
Einsteinium Es +2,+3
Fermium Fm +2,+3
Mendelevium Md +2,+3
Nobelium No +2,+3
Lawrencium Lr +3

6. 3. Actinide contraction
• The ionic radii of tripositive (M3+)and tetrapositive (M4+) actinide cations are shown in the
table
• The steady decrease in the size of M 3+ and M 4+ cations from left to right in the actinide
series is called actinide contraction and this is because of the poor screening of the nuclear
charge by the 5f electrons
i.e., On the addition of electron, one by one, to the poorly shielded 5f orbital of the actinide
series, the nuclear charge is also increased by +1 at each next element and the increasing
nuclear charge brings the valence shell nearer to the nucleus eventually the size of
M 3+ and M 4+ cation goes on decreasing as we move from one element to the next one in
the series.
ELEMENT Th Pa U Np Pu Am Cm Bk Cf
Radius M3+ (pm) 108 105 103 101 100 99 98.5 98 97.7
Radius M4+ (pm) 99 96 93 92 90 89 88 - -

7. 4.Colour of the Actinide cations
• The colour of the tripositive and tetra
positive actinide cations are given in the
table
• The actinide cations having 5f 0, 5f 1 and
5f 7 configuration are colorless while those
containing 5f 2, 5f 3, 5f 4, 5f 5 and 5f 6
configuration are colored
• These colors are produced when an
electron jumps from one energy level to
the other within 5f orbitals
Cation Configuration Colour
Ac 3+ 5f 06d07s0 colourless
U3+ 5f 36d07s0 red
Np 3+ 5f 46d07s0 purple
Pu 3+ 5f 56d07s0 violet
Am 3+ 5f 66d07s0 pink
Cm 3+ 5f 76d07s0 colourless
Th 4+ 5f 06d07s0 colourless
Pa 4+ 5f 16d07s0 colourless
U 4+ 5f 26d07s0 green
Np 4+ 5f 36d07s0 Yellow-green
Pu 4+ 5f 46d07s0 orange
Am 4+ 5f 56d07s0 red

8. 5. Formation of Complexes
• Most of the actinide halides are ready to form co-ordination compounds with alkali
metal halides
Example
ThCl4 + KCl → K[ThCl5]
ThCl4 + 2KCl → K2[ThCl6]
• The degree of complex formation for the ions M4+, MO2
2+, M3+ and MO2
+ decreases
in the order
M4+ > MO2
2+ > M3+ > MO2
+

9. Comparison between Lanthanides and Actinides

10. Thank you