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

Explanation

### Step-by-Step Solution

**Step 1: Definition of Lanthanoid Contraction**
Lanthanoid contraction refers to the gradual decrease in the ionic radii of the lanthanide series elements (from lanthanum to lutetium) as we move from left to right across the series. This contraction occurs due to the ineffective shielding of the nuclear charge by the f-electrons.

**Step 2: Explanation of Shielding Effect**
In the context of electron configuration, the shielding effect describes how inner electrons can shield outer electrons from the full effect of the nucleus's positive charge. In the case of lanthanides, the f-orbitals (where the f-electrons reside) provide poor shielding compared to s and p orbitals. This means that as more f-electrons are added, the outer electrons experience a stronger effective nuclear charge.

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