Chapter 7

Question 1

. What is the trend in atomic radii, and that in ionic radii, for the lanthanides? What are the exceptions to this, and why?

Answer 1

Question 2

2. Why do Eu and Yb have lower boiling points than the other lanthanides and significantly higher atomic radii?

Answer 2

Radius:

Because the screening ability of the f electrons is poor, the effective nuclear charge experienced by the outer electrons increases with increasing atomic number, so that the atomic radius would be expected to decrease, as is observed. Eu and Yb are exceptions to this; because of the tendency of these elements to adopt the (+2) state, they have the structure [Ln2+(e −)2] with consequently greater radii, rather similar to barium. Thus the atomic radii of europium and ytterbium are about 200 pm greater than might be predicted by interpolation from values for the flanking lanthanides. In contrast, the ionic radii of the Ln3+ ions exhibit a smooth decrease as the series is crossed

boiling: Their physical properties usually show smooth transition across the series, except that discontinuities are often observed for the metals that have a stable +2 state, europium and ytterbium. In terms of melting and boiling points, europium and ytterbium resemble calcium more closely than the neighboring lanthanides do. Similarly, Sm, Eu, and Yb have boiling points that are lower than those of the neighbouring metals. The lanthanide metals are soft, malleable and ductile. When freshly

Question 3

4. How can the rare earths be obtained in metallic form?

ohne 8!

Answer 3

Question 4

5. Explain why the +3 oxidation state is the most stable one for the lanthanides. Why do some of the lanthanides form relatively stable ions in the +2 or +4 oxidation state?

Answer 4

Question 5

7. What is the lanthanide contraction and what are consequences of this phenomenon?

Answer 5

Question 6

8. How can (anhydrous) halides of the divalent, trivalent and tetravalent lanthanides be prepared?

Answer 6

Question 7

3. Why have the early 4d and 5d transition metal elements very similar chemical properties?

Answer 7

Question 8

6. What are the most characteristic chemical properties of the trivalent lanthanide ions?

Answer 8

Kapitel 7 2/2

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