What is lanthanoid contraction? What are the consequences of lanthanold contraction?

Explanation

**Step-by-Step Text Solution:**

**Step 1: Define Lanthanoid Contraction**
Lanthanoid contraction refers to the gradual decrease in the size of the lanthanide series elements as we move from left to right across the series. This phenomenon occurs due to the poor shielding effect of the 4f inner electrons.

**Step 2: Explain the Cause of Lanthanoid Contraction**
The contraction is primarily caused by the fact that the 4f electrons do not shield the nuclear charge effectively. As a result, as we move from one element to the next in the lanthanide series, the effective nuclear charge experienced by the outer electrons increases, leading to a decrease in atomic and ionic radii.

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