The lanthanide contraction is an important concept in chemistry. Here’s a explanation:
Definition:
Lanthanide contraction refers to the gradual decrease in the size (atomic and ionic radii) of the lanthanide elements from lanthanum to lutetium as the atomic number increases, even though the number of electrons and protons is increasing.
Why it happens:
- As you move across the lanthanide series, electrons are added to the 4f orbitals.
- The 4f electrons do not shield the increasing positive charge of the nucleus very effectively.
- This means the outer electrons are pulled closer to the nucleus, making the atoms smaller.
Consequences of lanthanide contraction:
- The atomic and ionic sizes of elements decrease across the series.
- It affects the chemistry of elements after lanthanides, especially transition metals in period 6, making them similar in size to their period 5 counterparts.
- It influences oxidation states, density, and hardness of elements.
In short:
Lanthanide contraction is the shrinking of atomic size across the lanthanide series due to poor shielding by 4f electrons.