Lanthanoids and Actinoids
Lanthanoid contraction and comparative chemistry of the two series. (Chemistry › d- and f-Block Elements, NEET UG syllabus.)
What is Lanthanoids and Actinoids?
The series of 14 elements from Cerium (Ce, Z=58) to Lutetium (Lu, Z=71), where the 4f orbitals are progressively filled. Also known as 4f-series elements.
Key formula / rule: General Electronic Configuration (Lanthanoids)
Key points
- Define and explain lanthanoid contraction and its causes.
- Describe the consequences of lanthanoid contraction on subsequent elements and chemical properties.
- Compare and contrast the electronic configurations of lanthanoids and actinoids.
- Identify the common and characteristic oxidation states of lanthanoids and actinoids.
Common exam trap
Confusing the cause of lanthanoid contraction with actinoid contraction (both are due to poor shielding of f-electrons, but 4f vs 5f).
Definitions
- Term
Lanthanoids
- Meaning
The series of 14 elements from Cerium (Ce, Z=58) to Lutetium (Lu, Z=71), where the 4f orbitals are progressively filled. Also known as 4f-series elements.
- Term
Actinoids
- Meaning
The series of 14 elements from Thorium (Th, Z=90) to Lawrencium (Lr, Z=103), where the 5f orbitals are progressively filled. Also known as 5f-series elements.
- Term
Lanthanoid Contraction
- Meaning
The steady decrease in the atomic and ionic radii of the lanthanoids with increasing atomic number, primarily due to the poor shielding effect of 4f electrons.
Learning objectives
Define and explain lanthanoid contraction and its causes.
Describe the consequences of lanthanoid contraction on subsequent elements and chemical properties.
Compare and contrast the electronic configurations of lanthanoids and actinoids.
Identify the common and characteristic oxidation states of lanthanoids and actinoids.
Differentiate between lanthanoids and actinoids based on their radioactivity, complex formation tendency, and magnetic properties.
Explain the general trends in atomic and ionic radii for both series.
Formulae
- Name
General Electronic Configuration (Lanthanoids)
- Note
Exceptions exist, e.g., Gd (4f⁷ 5d¹ 6s²), Lu (4f¹⁴ 5d¹ 6s²).
- Expression
[Xe] 4f¹⁻¹⁴ 5d⁰⁻¹ 6s²
- Name
General Electronic Configuration (Actinoids)
- Note
More irregularities due to comparable energies of 5f, 6d, and 7s orbitals.
- Expression
[Rn] 5f¹⁻¹⁴ 6d⁰⁻¹ 7s²
Prerequisites
Basic understanding of atomic structure and electronic configuration.
Knowledge of periodic trends (atomic radius, ionization enthalpy, electronegativity).
Familiarity with d-block elements and transition metals.
Common mistakes
Confusing the cause of lanthanoid contraction with actinoid contraction (both are due to poor shielding of f-electrons, but 4f vs 5f).
Assuming all lanthanoids are radioactive (only Pm is).
Incorrectly stating the most common oxidation state for actinoids (it's +3, but higher states are also common and stable, unlike lanthanoids).
Not understanding the impact of lanthanoid contraction on the properties of elements in the d-block.
Mixing up the general electronic configurations of lanthanoids and actinoids.
Keywords
Lanthanoids
Actinoids
f-block
Inner transition elements
Lanthanoid contraction
4f electrons
5f electrons
Oxidation states
Radioactivity
Complex formation
Shielding effect
Atomic radii
Ionic radii
Practice preview
What is the primary reason for the lanthanoid contraction?…
easy
What is the most common and stable oxidation state exhibited by lanthanoids?…
easy
How do the oxidation states of actinoids generally compare to those of lanthanoids?…
medium