Lanthanides and Actinides

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Lanthanides and Actinides
The lanthanides and the actinides make up the f block of the periodic table. The lanthanides are the elements produced as the 4f sub level is filled with electrons and the actinides are formed while filling the 5f sub level Some significant similarities and differences between lanthanides and actinides are observed. The two rows that are generally placed underneath the main periodic table are called the lanthanides series and the actinides series. These two rows are produced when electrons are being added to f orbitals. Therefore this block of elements are referred to as the f block. The lanthanides are also occasionally referred to the rare earth elements.

Lanthanide and Actinide Series
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The f-block elements in which last electron or differentiating electron enter in (n-2) f-orbitals and the general electronic configuration is (n-2)f1-14(n-1)d0-1 ns2 consists of two series of inner transition elements-

Lanthanides (the fourteen element following lanthanum)
The elements in which the last electron enters one of the 4f-orbitals are called 4f-block elements or first inner transition series. They are also called Lanthanides (or) lanthanones because they come immediately after lanthanum. •

Actinides (the fourteen element following actinium)
The elements in which the last electron enters one of the 5f-orbitals are called 4f-block elements or second inner transition series. They are also called Actinides because they come immediately after actinium. The general electronic configuration is [Rn]5f1-14 6d0-1 7s2

Lanthanides (58Ce- 71Lu) - This series starts from Lanthanum ( atomic numbe r= 57) and continues up to the Lu (Lutetium) as shown in table above. All the elements of the lanthanide series resemble to each other very closely due to the presence of same number of electrons in outermost and the penultimate shells. They are also called rare earth elements. Though Lanthanum is a d-block element but included in lanthanides series as it resembles to them. General Characteristics

Some important characteristic are given below-
1.Electronic Configuration of Lanthanides: The general electronic configuration is. All have electronic configuration with 6s2 is common but variable occupancy of 4f and 5d-subshells due to the closeness in energy of 4f and 5d electrons. So it is considered that the 5d orbital remains vacant and the electrons enter into the 4f orbital. Exception are in case of gadolinium, Gd (Z = 64) where the electron enters into the 5d orbital due to the presence of half filled d-orbital and in Ytterbium (z = 70) in which all the 4f orbital's are completely filled and the differentiating electron of the next element that is lutetium (z = 71) enters in to the 5d orbital. The complete electronic configuration of Lanthanides can be given as 1s2 2s2 p6 3s2p6d104s2p6d10f0-14 5s2p6 d0-1 6s2. 2.Oxidation States: Lanthanides show variable oxidation states. The most stable oxidation state of Lanthanides is +3. They also show +2 and +4 oxidation states due to presence of either half filled or completely filled or empty 4f sub shell. 3.Color: Many of lanthanide metals are silver white. The lanthanide ions with +3 oxidation state are colored both in solid state and in aqueous solution. The color of a cation depends on the number of unpaired f electrons. 4.Magnetic Properties: The lanthanide ions other than f0 and f14 type are paramagnetic in nature due to unpaired electrons in f-orbitals. 5.Melting and boiling point: They have fairly high melting point but there is no definite trend in melting and boiling point of lanthanides. 6.Density: They has high density ranging between 6.77 to 9.74 g cm-3. Its increases with increasing atomic number. 7.Ionization enthalpies: They have low ionization enthalpy. 8.Complex formation: They don't have much tendency to form complexes because of low charge density. The order of complex formation can be best represented as Ln4+ > Ln3+ >...
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