Page 1 - Microsoft Word - Lesson note-4(f-block element )

SUBJECT-CHEMISTRY

CHAPTER-F-BLOCK ELEMENTS

SUBTOPIC- General trends in physical properties, lanthanides and
actinides.

KEY NOTES:

 Lanthanoids: The 14 elements immediately following lathanium are called lathanoids.
 Actinoids: The 14 elements immediately following actinium with atomic nos. 90-103
are called actinoids.
 When we move from left to right along a lanthanide series, there is a regular
decrease in the atomic and ionic radii as the atomic no. increases. This is called
lanthanide contraction.
 In the lanthanoids, La(II) and Ln(III) compounds are predominant species. However,
occasionally +2 and +4 ions in solution or in solid compounds are also obtained.

 The general trend in lanthanoids is observable in the actinoids as well.
There is a gradual decrease in the size of atoms or M3+ ions across the
series. This may be referred to as the actinoid contraction (like
lanthanoid contraction). The contraction is, however, greater from
element to element in this series resulting from poor shielding by 5f
electrons.