Essay about Lanthanides and Actinides

2108 Words Dec 11th, 2012 9 Pages
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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Thus, there is a gradual increase in the effective nuclear charge experienced by the outer electrons. So the attraction of the nucleus for the electrons in the outermost shell increases as the atomic number increases and the electron cloud shrinks.
This results in gradual decrease in size of lanthanides with increasing atomic number. The decrease in size is not regular throughout the lanthanides. A rapid decrease is seen only in first six elements compared to the rest of the elements. Consequences of lanthanide contraction
1. Similarity of second and third transition series- Generally the size of atoms increases down a group. So the size of atom of element of second transition series is larger than any atom of first transition series but the size of atom of third transition series is nearly same as that of atom of second transition series. The similarity in the size of atoms of the elements belonging to the same group of the second and third transition series is due to the effect of lanthanide contraction. For example- radius of Zr radius of Hf & radius of Nb radius of Ta etc.
2. Difficulty in the separation of lanthanides- As there is small change in the ionic radii of lanthanides so their chemical properties are similar. This makes the separation of elements in the pure state difficult. This contraction makes the slight difference in size so the properties like solubility, complex formation, hydration etc shows some differences and its

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