Which element among the lanthanides has the smallest atomic radius

Understanding the Lanthanide Series

The lanthanides are a group of 15 elements ranging from lanthanum (La) to lutetium (Lu) in the periodic table. These elements are characterized by their filling of the 4f orbitals and share many similar chemical properties.

Atomic Radius Trends in the Lanthanide Series

When considering "which element among the lanthanides has the smallest atomic radius," it is important to note the general trend across the series. As we move from left to right (from La to Lu), the atomic radius decreases. This reduction is due to the increase in the number of protons, which enhances the effective nuclear charge. As a result, the electrons are pulled closer to the nucleus, leading to a smaller atomic size.

The Role of Lanthanide Contraction

The phenomenon known as "lanthanide contraction" plays a crucial role in determining which element among the lanthanides has the smallest atomic radius. This contraction occurs due to the poor shielding effect of the 4f electrons. These electrons are less effective at countering the increased nuclear charge, causing a progressive decrease in atomic size as we move across the lanthanide series.

Comparison of Atomic Radii

Among the lanthanides, the elements listed for comparison are:

• Cerium (Ce)
• Europium (Eu)
• Gadolinium (Gd)
• Lutetium (Lu)

To identify which element among the lanthanides has the smallest atomic radius, we analyze the positions of these elements in the series:

• Cerium (Ce): Positioned near the start of the lanthanide series, it has a relatively larger atomic radius.
• Europium (Eu) and Gadolinium (Gd): Positioned in the middle of the series, their atomic radii are smaller than Cerium but larger than Lutetium.
• Lutetium (Lu): The final element in the series, it has the smallest atomic radius due to the maximum effective nuclear charge and the effects of lanthanide contraction.