Text 18

Rubidium and cesium

Rubidium and cesium are the fourth and fifth members of the alkali metal group. Rubidium and cesium were discovered by Bunsen and Kirchhoff in 1860 and 1861, respectively by the use of the spectroscope. Rubidium was named for the prominent red lines in its spectrum, and cesium for its prominent blue lines. Both elements are soft, ductile, low-density, silvery-white metals of low melting points.

In both physical and chemical properties, rubidium and cesium resemble the other alkali metals. They are monovalent in their compounds, which are very stable to oxidation and reduction. Rubidium and cesium are the second and the first most electropositive elements and the second and first most alkaline elements.

Physical properties

About 27.2% of ordinary rubidium is beta - emitting rubidium 87 with a half life of 6.3 * 107 years. It decomposes to strontium, and can be used to determine the age of rubidium- containing rocks.

The only natural isotope of cerium is cesium 133, but cerium 137 is one of the products of the atomic fission of uranium. It is also a beta emitter and has a half life of 33 years. Along with strontium 90, it is one of the most trouble some radioactive wastes to handle in the commercial applications of atomic fission.

Among the most interesting physical properties of rubidium and cesium are their large ionic radii, their low ionization potentials, their low densities and melting points, their high position in the electromotive series, and their low electron work functions. Both metals are photosensitive and are ionized readily and efficiently by visible light and by infra- red and ultra- violet radiations.

Occurrence

Rubidium is the sixteenth most prevalent element in the earth's crust but is not found in any mineral as a principal constituent. Rather, it occurs widely dispersed in potassium minerals in very low concentrations.

This lack of concentration in any mineral deposits undoubtedly accounts for the scarcity of production and application of this rather prevalent element, however it is also found in lepidolites ores of South Africa, some of the lepidolites containing as much as 1 to 1.5 per cent rubidium and much smaller amounts of Cs. The extensive processing of these lithium ores has resulted in an increasing availability of rubidium and cesium by- product concentrates that are being used as sources of rubidium and cesium compounds.

Cesium is the fortieth most prevalent element in the earth's crust and is found in minerals such as pollucite (2Cs2O.2Al2O3.9SiO2.H2O), a hydrated silicate of aluminium and cesium.

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Exercises

I. Answer the following question:

1. Who discovered rubidium and cesium?

2. When were these elements discovered?

3. What do the names "rubidium" and "cesium" mean?

4. What do you know about the physical properties of rubidium and cesium?

5. What can you tell about rubidium 87?

6. Which element is considered to be one of the products of atomic fission of uranium?

II. Translate the following derivatives:

1. Alkali, alkaline, alkalinity, alkalinous, alkalization, alkalize, alkalizing;

2. Concentrate, concentrated, concentrating, concentration, concentrator;

3. Decompose, decomposer, decomposing, decomposition;

4. Disperse, dispersed, disperser, dispersing, dispersion, dispersity, dispersive;

5. Reduce, reduced, reducer, reducing, reduction;

III. Translate the following sentences paying the attention to the bold type:

1. Both rubidium and cesium are photosensitive and are ionized readily by visible light.

2. Both metals react very vigorously with water.

3. In both physical and chemical properties, rubidium and cesium resemble the other alkali metals.

4. Both elements are soft, ductile, low-density metals.

5. Both rubidium and cesium halides form double halide complexes with such metals as antimony, bismuth, cobalt, etc.

6. Both elements form a series of polyhalides wherein two of the halide atoms must be of valence -1 and third of valence +1.

IV. Translate the following sentences paying the attention to the bold type:

1. Rubidium is not found in mineral as principal constituent. Rather, rubidium occurs widely dispersed in potassium minerals in very low concentrations.

2. Since rubidium and cesium are easily ionized at rather low temperature, they offer great potential.

3. Since ancient times, it has been known that silicous material were suitable for glass- making.

4. The fats and oils are esters of special class, (in) as much as all are derived from glycerol.

5. Some of the lepidolites containing as much as 1 to 1.5 per cent rubidium and much smaller amounts of cesium.

6. The presence of as little as 0.01 mg of tellurium per cubic meter of air gives rise to the characteristic foul breath.

7. Many crystals break most readily along certain planes where the cohesive forces are weaker than in other directions.

8. Along with strontium 90, cesium 137 is one of the most radioactive wastes to handle.

9. In 1925 Ungerer observed a separation of small ions on account of their different sizes when he studied their adsorption on clay.

10. The lack of concentration in any mineral deposits accounts for the scarcity of production and application of such rather prevalent element as rubidium.

11. Cesium is found in minerals such as polucite, a hydrated silicate of aluminium and cesium.

12. Only oxygen is more abundant on the earth's crust than silicon.

13. The only natural isotope of cesium is cesium 133.

14. Most commercial rare earth salts contain the rare earths in much the same ratio as they occur in the ore.

V. Translate the following sentences paying the attention to the singular and plural forms:

1. Alkali, alkalis, alkalies;

2. Datum, data;

3. Nucleus, nuclei;

4. Phenomenon, phenomena;

5. Radius, radii;

6. Series, series;

7. Spectrum, spectra;

VI. Translate the following sentences into English:

1. Rubidi vµ cesi thuéc nhãm 1 cña hÖ thèng tuÇn hoµn c¸c nguyªn tè ho¸ häc.

2. Khi lµm viÖc víi rubidi vµ cesi cÇn ph¶i nhí c¶ hai nguyªn tè nµy ®Òu kh«ng bÒn ®èi víi ph¶n øng oxi ho¸ vµ khö.

3. Nh­ ®• biÕt, rubidi vµ cesi ®¬n chÊt cã thÓ ®­îc diÒu chÕ b»ng mét sè ph­¬ng ph¸p.

4. Ng­êi ta cho r»ng ph­¬ng ph¸p ®­îc sö dông réng r•i nhÊt lµ ph­¬ng ph¸p nung cacbonat cña rubidi vµ cesi víi magie ë nhiÖt ®é 6750 C trong khÝ quuyÓn hydro.

5. CÇn ph¶i nhí r»ng, Cs137 lµ mét trong nh÷ng s¶n phÈm cña sù ph©n r• h¹t nh©n uran.

VII. Make an outline of the text.

VIII. Retell the text