Inner transition elements

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 INNER TRANSITION ELEMENTS: ACTINIDES

2. INNER TRANSITION ELEMENTS: ACTINIDES 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: 5f 1-14 6d 7s 2 including Actinium are called Actinides  

3. INNER TRANSITION ELEMENTS: ACTINIDES 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. INNER TRANSITION ELEMENTS: ACTINIDES 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. INNER TRANSITION ELEMENTS: ACTINIDES 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 5f 14 (completely filled) configuration In Am and Bk , the moderately stable oxidation states are +2 and +4 respectively and these are on account of their 5f 7 (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. INNER TRANSITION ELEMENTS: ACTINIDES 3. Actinide contraction The ionic radii of tripositive (M 3+ )and tetrapositive (M 4+ ) 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 M 3+ (pm) 108 105 103 101 100 99 98.5 98 97.7 Radius M 4+ (pm) 99 96 93 92 90 89 88 - -

7. INNER TRANSITION ELEMENTS: ACTINIDES 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 , 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 6d 7s colourless U 3+ 5f 3 6d 7s red Np 3+ 5f 4 6d 7s purple Pu 3+ 5f 5 6d 7s violet Am 3+ 5f 6 6d 7s pink Cm 3+ 5f 7 6d 7s colourless Th 4+ 5f 6d 7s colourless Pa 4+ 5f 1 6d 7s colourless U 4+ 5f 2 6d 7s green Np 4+ 5f 3 6d 7s Yellow-green Pu 4+ 5f 4 6d 7s orange Am 4+ 5f 5 6d 7s red

8. INNER TRANSITION ELEMENTS: ACTINIDES 5. Formation of Complexes Most of the actinide halides are ready to form co-ordination compounds with alkali metal halides Example ThCl 4 + KCl → K[ThCl 5 ] ThCl 4 + 2KCl → K 2 [ThCl 6 ] The degree of complex formation for the ions M 4+ , MO 2 2+ , M 3+ and MO 2 + decreases in the order M 4 + > MO 2 2 + > M 3+ > MO 2 +

9. INNER TRANSITION ELEMENTS: ACTINIDES Comparison between Lanthanides and Actinides

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