In 1861, the recently invented physical method for studying substances - spectral analysis - once again demonstrated its power and reliability, as a guarantee of a great future in science and technology. With its help, the second previously unknown chemical element, rubidium, was discovered. Then, with the discovery of the periodic law by D. I. Mendeleev in 1869, rubidium, together with other elements, took its place in the table, which introduced order into chemical science.
Further study of rubidium showed that this element has a number of interesting and valuable properties. We will consider here the most characteristic and important of them.
General characteristics of a chemical element
Rubidium has an atomic number of 37, that is, in its atoms the composition of the nuclei includes just such a number of positively charged particles - protons. Accordingly, the neutral atom has 37 electrons.
The symbol of the element is Rb. In the periodic system, rubidium is classified as an element of group I, the period is fifth (in the short-period version of the table it belongs to the main subgroup of group I and is located in the sixth row). It is an alkali metal, it is a soft, very low-melting crystalline substance of silver-white color.
Discovery history
The honor of discovering the chemical element rubidium belongs to two German scientists - the chemist Robert Bunsen and the physicist Gustav Kirchhoff, the authors of the spectroscopic method for studying the composition of matter. After the use of spectral analysis led to the discovery of cesium in 1860, scientists continued their research, and as early as next year, when studying the spectrum of the lepidolite mineral, they discovered two unidentified lines of dark red color. It was thanks to the characteristic shade of the most powerful spectral lines, by which it was possible to establish the existence of an element previously unknown, that it got its name: the word rubidus is translated from Latin as “crimson, dark red”.
In 1863, Bunsen first isolated metal rubidium from the water of a mineral spring by evaporation of a large amount of solution, separation of potassium, cesium and rubidium salts and, finally, metal reduction using soot. Later N. Beketov was able to restore rubidium from its hydroxide using aluminum powder.
Physical characteristic of an element
Rubidium is a light metal, it has a density of 1.53 g / cm 3 (at zero temperature). Forms crystals with a cubic body-centered lattice. Rubidium only melts at 39 ° C, that is, at room temperature its consistency is already close to pasty. The metal boils at 687 ° C; its vapors have a greenish-blue tint.
Rubidium is a paramagnet. In conductivity, it is more than 8 times superior to mercury at 0 ° C and almost as much as inferior to silver. Like other alkali metals, rubidium has a very low threshold for photoelectric effect. To excite the photocurrent, long-wavelength (that is, low-frequency and carrying less energy) red light rays are sufficient in it. In this respect, only cesium is superior in sensitivity.
Isotopes
Rubidium has an atomic weight of 85.468. It is found in nature in the form of two isotopes that differ in the number of neutrons in the nucleus: rubidium-85 makes up the largest share (72.2%), and in a much smaller amount - 27.8% - rubidium-87. The nuclei of their atoms, in addition to 37 protons, contain 48 and 50 neutrons, respectively. The lighter isotope is stable, and rubidium-87 has a huge half-life of 49 billion years.
Currently, several dozens of radioactive isotopes of this chemical element have been artificially produced: from ultralight rubidium-71 to neutron-rich rubidium-102. The half-lives of artificial isotopes range from a few months to 30 nanoseconds.
Basic chemical properties
As noted above, in the series of chemical elements, rubidium (such as sodium, potassium, lithium, cesium, and France) belongs to alkali metals. The peculiarity of the electronic configuration of their atoms, which determines the chemical properties, is the presence of only one electron at the external energy level. This electron easily leaves the atom, and the metal ion in this case acquires an energetically favorable electronic configuration of the inert element in front of it in the periodic table. For rubidium, this is a krypton configuration.
Thus, rubidium, like other alkali metals, has pronounced reducing properties and an oxidation state of +1. Alkaline properties are more pronounced with increasing atomic weight, since the radius of the atom also increases, and, accordingly, the bond of the external electron with the nucleus is weakened, which leads to an increase in chemical activity. Therefore, rubidium is more active than lithium, sodium and potassium, and cesium, in turn, is more active than rubidium.
Summarizing all of the above about rubidium, the analysis of the element can be done, as in the illustration below.
Rubidium Compounds
In air, this metal, due to its exceptional reaction activity, oxidizes violently, with ignition (the flame has a purple-pinkish color); during the reaction, peridoxide and rubidium peroxide are formed, exhibiting the properties of strong oxidizing agents:
- Rb + O 2 → RbO 2 .
- 2Rb + O 2 → Rb 2 O 2 .
An oxide is formed if oxygen access to the reaction is limited:
It is a yellow substance that reacts with water, acids and acid oxides. In the first case, one of the strongest alkalis is formed - rubidium hydroxide, in the rest - salts, for example, rubidium sulfate Rb 2 SO 4 , most of which are soluble.
Even more violently, accompanied by an explosion (since both rubidium and released hydrogen instantly ignite), the metal reacts with water, in which rubidium hydroxide is formed, an extremely aggressive compound:
- 2Rb + 2H 2 O → 2RbOH + H 2 .
Rubidium is a chemical element that can also directly react with many non-metals - with phosphorus, hydrogen, carbon, silicon, and halogens. Rubidium halides - RbF, RbCl, RbBr, RbI - are readily soluble in water and in some organic solvents, for example, ethanol or formic acid. The interaction of metal with sulfur (grinding with sulfur powder) occurs explosively and leads to the formation of sulfide.
There are also sparingly soluble rubidium compounds, such as RbClO 4 perchlorate; they are used in analytics to determine this chemical element.
Being in nature
Rubidium is an element that is not a rare one. It is found almost everywhere, is part of many minerals and rocks, and is also found in the ocean, in underground and river waters. In the earth's crust, the rubidium content reaches the total content of copper, zinc and nickel. However, unlike many much rarer metals, rubidium is an extremely dispersed element, its concentration in the rock is very low, and it does not form its own minerals.
In the composition of minerals, rubidium is commonly associated with potassium. The highest concentration of rubidium is characterized by lepidolites - minerals that also serve as a source of lithium and cesium. So rubidium in small quantities is always present where other alkali metals are found.
A bit about the use of rubidium
Brief description of chem. The rubidium element can be supplemented with a few words about the areas in which this metal and its compounds are used.
Rubidium is used in the production of photocells, in laser technology, and is part of some special alloys for rocket technology. In the chemical industry, rubidium salts are used due to their high catalytic activity. One of the artificial isotopes, rubidium-86, is used in gamma-ray inspection and, in addition, in the pharmaceutical industry for the sterilization of drugs.
Another isotope, rubidium-87, is used in geochronology, where it is used to determine the age of the oldest rocks due to the very long half-life (rubidium-strontium method).
If several decades ago it was believed that rubidium is a chemical element, the scope of which is unlikely to expand, then at present new prospects for this metal appear, for example, in catalysis, in high-temperature turbine units, in special optics, and in other fields. So in modern technology, rubidium plays and will continue to play an important role.