Inner Transition Elements: (f-block elements) – Lanhanoides and Actinoides

The inner transition elements are divided into two categories Lanthanoide and actinoides. The Lanthanoides (At. no. 58 – 71) comes immediately after Lanthanum. They have general electronic configuration 4f^1-145d^0-16s². The Actinoides (At. no. 90 – 103) comes immediately after actinium. They have general Electronic configuration 5f^1-146d^0-17s². The electronic configuration of Lanthanoids and Actinoids is given below:

Lanthanoids Element        Symbol      At.No.          Elect.Conf. [Xe]				Actinoids Element        Symbol      At.No.          Elect.Conf. [Rn]
Lanthanum	La	57	5d16s2	Actinium	Ac	89	6d17s2
Cerium	Ce	58	4f25d06s2	Thorium	Th	90	6d27s2
Praseodynium	Pr	59	4f35d06s2	Protactinium	Pa	91	5f26d17s2
Neodymium	Nd	60	4f45d06s2	Uranium	U	92	5f36d17s2
Promethium	Pm	61	4f55d06s2	Naptunium	Np	93	5f46d07s2
Samarium	Sm	62	4f65d06s2	Plutonium	Pu	94	5f66d07s2
Europiom	Eu	63	4f75d06s2	Americium	Am	95	5f76d07s2
Gadolinium	Gd	64	4f75d16s2	Curium	Cm	96	5f76d17s2
Terbium	Tb	65	4f95d06s2	Berklium	Bk	97	5f96d07s2
Dysprosium	Dy	66	4f105d06s2	Californium	Cf	98	5f106d07s2
Holmium	Ho	67	4f115d06s2	Einsteinium	Es	99	5f116d07s2
Erbium	Er	68	4f125d06s2	Fermium	Fm	100	5f126d07s2
Thulium	Tm	69	4f135d06s2	Mendelevium	Md	101	5f136d07s2
Ytterbium	Yb	70	4f145d06s2	Nobelium	No	102	5f146d07s2
Lutetium	Lu	71	4f145d16s2	Lowrencium	Lr	103	5f146d17s2

1. Oxidation State of Lanthanoides:- All lanthanoides exhibit a common stable oxidation state of +3. In addition of it some Lanthanoides show +2 and +4 oxidation states also. These oxidation states are shown by those elements which acquire f⁰, f⁷ or f¹⁴ configuration by doing so. Cerium (At. No. = 58) exhibits the +4 O.S. predominately.
2. Atomic size (Lanthanoides Contraction):- In Lanthanoides series the nuclear charge increases in the atomic no. there is a progressive decrease in atomic as well as ionic radius (+3 O.S) form La to Lu. This regular decreases in size is called Lanthanoide contraction.

Cause of Lanthanoide Contraction:- As we move along the Lanthanoides series the nuclear charge increases by one unit each time. The new electrons is added into the same sub shell (4f) as a result of it, the attraction on the electrons by the nucleus increases and tends to decreases and tends to decrease the size. The increased nuclear charge due to imperfect shielding by the out wayed f-orbitals. Hence net result is the decrease in size of atoms (ions) from La to Lu.

Consequences of Lanthanoide Contraction:-

1. There is a similarly in size of the elements belonging to 2^nd and 3^rd transition series elements even after the fact that size increases on moving down the group.
2. The properties of Lanthanides are quite similar, but due to the small difference in their size the ability to form complexes vary which is used in separation of lanthanides.
3. Basic Strength of hydroxides decreases from La(OH) to Lu(OH) to Lu(OH)₃ because of the decreases in the size of trivalent ion from La to Lu.

3. General Characteristics of Lanthanoids:-

Lanthnoids are silvery white soft metals and tarnish rapidly in air. They are hard with high M.Pt., good conductors of heat and electricity. Many trivalent cations are coloured both in solid state and in aq. Solution. La³⁺ show no colour because there are no unpaired electrons. The general reactions of lanthanoids is represented as:

Use of Lanthanides:-

1. Caeric Sulphate is used as oxidizing agent is volumetric analysis.
2. An alloy of Lanthanide is used to make parts of jet engine.
3. The oxides of Lanthanides are used in polishing mirror.

Cerium salts are used as dyes and catalyst.