The Lanthanoids

The Lanthanoids:

·        It is a series of 14 elements

·        They are also known as f block element

·        Elements from atomic number 58 to 71 come in this series

·        General electronic configuration of the element of this series is 4f^1-14, 5d^0-1, 6s²

1)  Position in Periodic table:

In periodic table these 14 elements are placed separately at the bottom of table.  But actually it follows lanthanum (Z=57) of the 6^th period and group 3. Thus:

Lanthanoids belong to group 3 and sixth period of the periodic table.

(Only for sake of convenience these elements are shown at the bottom of the periodic table as lanthanoid series)

2) Electronic Configuration:

The atom of these elememts have electronic configuration with 6s2 common but their occupancy of 4f level is variable.

In this series, electrons are progressively filled in 4f orbital. Therefore the series is also known as 4f series.

The electronic configuration of lanthanoid series are :

4f^1-14, 5d^0-1, 6s² (where n=1-14 with increasing atomic number)

3) Atomic and Ionic size:

With increase in atomic number, the atomic and ionic radii of the element of the lanthanoid series gradually decrease.

This is called lanthanoid contraction and it is a unique feature of the lanthanoid series.

4) Oxidation State:

The common oxidation state of lanthanoids is +3. It is due to the loss of two 6s electrons and one 5d or 4f electron.

However some of the lanthanoids also show either +2 or +4 oxidation state.

5) Physical Properties: 

Lanthanoids show following physical properties:

• ·        The hardness of the lanthanoid increases with atomic number
• ·        Their melting point ranges between 1000 to 1200 k
• ·        They show metallic structure and nature
• ·        Except La+3 and Lu+3, lanthanoids show coloured ions(because of f block)

  6) Chemical Properties:

Lanthanoids show following chemical properties:

·        When lanthanoids are heated around 2500⁰C with carbon, they form carbides

·        When lanthanoids are gently heated with the hydrogen gas, the metal combine with hydrogen and form hydrides

·        When lanthanoids are burnt in oxygen,, they form oxide

·        On heating with nitrogen, lanthanoids form nitrides

·        When lanthanoids are treated with mineral acid, they liberate H2 gas.

·        When lanthanoids are treated with water, they form consequently hydroxides and liberate hydrogen gas

·        On heating with sulphur, lanthanoids form corresponding sulphides