Question 1

What is the differentiating electron in the lanthanoid series?

Accepted Answer

The differentiating electron enters the inner 4f subshell. The general pattern is written as [Xe] 4f¹–¹⁴ 5d⁰–¹ 6s², with the exact 5d occupancy varying between elements.

Question 2

Why is +3 the most common oxidation state of lanthanoids?

Accepted Answer

The lanthanoids commonly lose the two 6s electrons and one outer electron to form Ln3+ ions. Eu and Yb have notable +2 states, while Ce and Tb can also show +4.

Question 3

What causes lanthanoid contraction?

Accepted Answer

As nuclear charge increases from La to Lu, the added 4f electrons provide poor shielding. The effective attraction of the nucleus therefore increases, producing a gradual decrease in Ln3+ ionic radii.

Question 4

Why are zirconium and hafnium so similar in size?

Accepted Answer

The similar sizes of Zr and Hf are a major consequence of lanthanoid contraction. Their nearly matching radii make their chemical properties strongly alike.

Question 5

How does lanthanoid contraction affect hydroxide basicity?

Accepted Answer

As the lanthanoid ions become smaller from La to Lu, the basicity of the corresponding hydroxides decreases. The changing ion size is the key comparison to remember.

Lanthanoid Series: 4f Squeeze and the +3 State

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