Lanthanoids are also called as lanthanides and are a group of 15 elements in the periodic table, ranging from Lanthanum (La, atomic number 57) to Lutetium (Lu, atomic number 71). These elements belong to the f-block of the periodic table and are also known as rare earth metals.
The name “lanthanoids” comes from the first element in the series, lanthanum. Although the lanthanum itself is a d-block element, it is often included in the lanthanoid series due to its chemical similarity with the other elements in the group.
Electronic Configuration of Lanthanoids
The general electronic configuration of lanthanoids is:
[Xe]4f1−14 5d06s2
Where Xe represents the noble gas Xenon (atomic number 54).
As we move across the lanthanoid series, electrons are added to the 4f orbital.
The 4f orbitals are deeply buried inside the atom and are shielded by the 5d and 6s orbitals.
This shielding effect leads to minor variations in chemical properties across the series.
Occurrence of Lanthanoids
Lanthanoids are not as rare as their name suggests. Some of the most common minerals containing lanthanoids are:
Monazite (Ce, La, Th)PO₄
Bastnaesite (Ce, La, Nd)CO₃F
Xenotime (YPO₄)
They are found in small amounts in various minerals and are extracted by using complex separation techniques.
Extracting lanthanoids (Rare Earth Elements, REEs) from minerals is a complex process due to their similar chemical properties. The extraction process normally are multiple sophisticated techniques:
1.Ore Processing and Beneficiation
Crushing & Grinding: The ore is crushed and ground to release rare earth minerals.
Gravity Separation: Some heavy rare earth minerals (like monazite) can be separated based on density.
Flotation: Chemical reagents are used to selectively float REEs while leaving gangue materials behind.
Magnetic & Electrostatic Separation: These methods help to separate rare earth minerals from impurities based on magnetic susceptibility and conductivity differences.
2. Chemical Processing & Leaching
Acidic Leaching: Concentrated acids (H₂SO₄, HCl, or HNO₃) dissolve REEs from the ore.
Alkaline Leaching: Applied to some ores (e.g., bastnäsite) using NaOH to remove impurities before acid dissolution.
In-Situ Leaching: Used in some cases where chemicals are injected directly into the ore deposit underground.
3. Solvent Extraction (SX)
One of the most effective methods for separating REEs.
Organic solvents selectively extract REEs from an aqueous phase.
Multiple stages are required to separate individual elements due to their close chemical properties.
4. Ion Exchange
Uses resin columns to selectively bind REEs, which are later eluted using appropriate solutions.
This method is precise but slow and costly.
5. Precipitation & Purification
Selective Precipitation: Adjusting pH to selectively precipitate certain REEs as hydroxides, oxalates, or carbonates.
Calcination: Heating the precipitated compounds to obtain pure rare earth oxides.
6. Electrowinning & Electrorefining
In some cases, REEs can be extracted by electrodeposition from a solution.
Used mainly for high-purity refining of individual lanthanides.
7. Liquid–Liquid Extraction (LLE)
A more advanced form of solvent extraction that allows for precise separation of different REEs.
8. Molten Salt Electrolysis
Used to produce pure lanthanoid metals from their oxides by reducing them in molten fluoride salts.
These techniques are often used in combination to achieve high purity and separation efficiency.
Properties of Lanthanoids
Physical Properties
1.Metallic Nature: Lanthanoids are silvery-white metals that are soft and malleable.
2. Density: The density increases gradually across the series.
3.Melting and Boiling Points: These are relatively high but show no regular trend.
4. Magnetic Properties: Many lanthanoids exhibit paramagnetism (attracted to a magnetic field) due to unpaired electrons in the 4f orbitals.
5. Oxidation State: The most common oxidation state of lanthanoids is +3 (Ln³⁺), but some also show +2 and +4 states.
Chemical Properties
1. Electropositivity: Lanthanoids are highly electropositive and reactive.
2. Reaction with Air: They tarnish in air due to the formation of an oxide
3. Reaction with Water: They react slowly with water, forming hydroxides.
4. Reaction with Acids: Lanthanoids dissolve in dilute acids, releasing hydrogen gas.
5. Complex Formation: They form weak complexes because 4f orbitals do not participate in bonding.
Lanthanide Contraction
A unique feature of lanthanoids is the lanthanide contraction the gradual decrease in atomic and ionic radious from La to Lu. This occurs because:
The increasing nuclear charge pulls the 4f electrons closer to the nucleus.
Poor shielding by the 4f electrons leads to a stronger attraction between the nucleus and outer electrons.
Effects of Lanthanide Contraction
1. Similarities in Properties: Due to small size differences, elements after lanthanoids (like Hf, Ta, and W) have properties similar to their corresponding transition elements.
2. Decrease in Basic Character: Lanthanoid hydroxides become less basic from La(OH)₃ to Lu(OH)₃.
3. Separation of Lanthanoids: Due to their similar size, separating lanthanoids from each other is difficult.
Uses of Lanthanoids
Lanthanoids have many industrial and scientific applications:
1. Catalysts – Used in petroleum refining and chemical industries.
2. Magnets – Neodymium (Nd) is used in strong permanent magnets.
3. Alloys – Mixed with other metals to improve strength and resistance to corrosion.
4. Glass & Ceramics – Used in optical glasses, camera lenses, and ceramics.
5. Lasers & Electronics – Yttrium-based lanthanoids are used in lasers, superconductors, and TV screens.
6. Medical Applications – Gadolinium compounds are used in MRI contrast agents.
Comparison: Lanthanoids vs Actinoids
Lanthanoids are often compared to actinoids (elements from Ac to Lr). The differences are tabulated below:
Property | Lanthanoids | Actinoids |
Electronic Configuration | 4f filling | 5f filling |
Oxidation States | Mostly +3 | Variable (+3, +4, +5, etc.) |
Reactivity | Less reactive | More reactive |
Magnetic Properties | Mostly paramagnetic | More complex behaviuor |
Radioactivity | Mostly non-radioactive | Mostly radioactive |
Summary
Lanthanoids are a interesting group of elements with unique electronic structures, chemical properties, and industrial applications. Their gradual size decrease (lanthanide contraction) plays a vital role of the uses in technology, medicine and industry.
Lanthanoids are a series of 15 elements in the periodic table, ranging from Lanthanum (La, atomic number 57) to Lutetium (Lu, atomic number 71). They belong to the f-block and are known as rare earth metals.
Lanthanide contraction is the gradual decrease in atomic and ionic radious of lanthanoids from La to Lu due to poor shielding of 4f electrons, which increases the effective nuclear charge.
The most common oxidation state of lanthanoids is +3 (Ln³⁺), but some also show +2 and +4 oxidation states.
Lanthanoids have similar chemical properties because:
They all have the same outer electronic configuration ([Xe] 4f¹⁻¹⁴ 5d⁰ 6s²).
The 4f electrons do not participate much in bonding.
Lanthanoids are used in:
Magnets (Neodymium in powerful magnets)
Lasers and Electronics (TV screens, superconductors)
Catalysts (Petroleum refining)
Medical Imaging (Gadolinium in MRI contrast agents)
Feature | Lanthanoids | Actinoids |
Electron filling | 4f orbitals | 5f orbitals |
Oxidation states | Mostly +3 | Variable (+3, +4, +5, etc.) |
Reactivity | Less reactive | More reactive |
Radioactivity | Mostly non-radioactive | Mostly radioactive |