O rubidium, with atomic number 37 and atomic mass of 85.5 u, is a very soft alkali metal, white or silver in color. Like other alkali metals, this element reacts violently with water and air. Its melting point is 39 °C, while its boiling point is 688 °C.
It was discovered in 1861 by German scientists Gustav Kirchhoff and Robert Bunsen during analysis of the mineral lepidolite with a spectroscope. It can be used in the manufacture of photocells, special glasses and as a propellant in spacecraft ion engines. Rubidium forms a large number of compounds, although none of them have significant commercial application yet.
Read too: Carbon — one of the most abundant elements in the universe
Summary
alkali metal of atomic number 37 and atomic mass 85.5 u.
It has a silvery-white color.
It was discovered in 1861 by Gustav Kirchhoff and Robert Bunsen.
Reacts violently with water and can spontaneously burn on contact with air.
It is very soft, just like other alkali metals.
It is used in the manufacture of special glasses and atomic clocks.
Rubidium properties
Symbol: Rb
atomic mass: 85.5 u.
atomic number: 37.
electronegativity: 0,82.
Density: 1.53 g/cm³.
Fusion point: 39°C.
Boiling point: 668°C.
electronic configuration: [Kr] 5s1.
chemical series: alkali metals.
Rubidium characteristics
like whole metallic element, the rubidium has a characteristic shine, in addition to a white or silver color. As it belongs to the group of alkali metals in the periodic table, rubidium has the classic characteristics of this family, such as the fact that it is not very dense compared to other metals. extremely soft — it can even be cut with a simple knife — and also because it reacts violently with water, forming a basic compound (alkaline), as the reaction shows the follow:
2 Rb (s) + H2O (1) → 2 RbOH (here) + H2(g)
O hydrogen generated in this reaction is ignited when encountering the oxygen present in the air. The rubidium, including, can ignite on its own in contact with air because of the oxygen present in it and, therefore, its handling requires care, after all, another classic characteristic of alkali metals is that they are very reactive. The reaction below shows the reaction of rubidium with oxygen, forming an oxide with an alkaline character.
4 Rb (s) + O2(g) → 2 Rb2O (s)
Compared to other alkali metals of lower atomic ray (lithium, sodium and potassium), the Reactions of rubidium with water or oxygen are more violent, since its valence electron has greater energy.
Read too: Niobium — a metal with various industrial and commercial applications
Rubidium history
the rubidium was discovered in 1861 by German scientists Gustav Kirchhoff and Robert Bunsen, in the city of Heidelberg, Germany. Using their newly invented instrument, the spectroscope, Kirchhoff and Bunsen performed analysis of samples until they found two new elements: cesium (Cs), in mineral water, and rubidium, in mineral lepidolite.
The name rubidium comes from the color of its spectral emission line, which is red (rubidius, in Latin). Bunsen even managed to isolate metallic rubidium samples.
Where is Rubidium found?
No ore has rubidium as a priority constituent. Its greatest occurrence is as a by-product in lepidolite and polucite, which may contain 3.5% and 1.5% rubidium oxide, respectively. Reserves of this mineral are spread all over the world, as in Australia, Canada, China, Namibia and Zimbabwe, however the processes of extraction and processing of the mineral still have prohibitive costs.
Rubidium Applications
O special glass market is the main one for rubidium, as well as photocells. As well as its similar cesium, rubidium is also used in the manufacture of atomic clocks, devices of extreme precision and of extreme importance for the calibration of GPS, the Global Positioning System. The difference with cesium clocks is that rubidium atomic clocks, in addition to being low-cost, can be manufactured for that are about the size of a matchbox and yet remain accurate by millions or even billions of years old.
![Cesium Atomic Clock, located in Germany, which will maintain accuracy for 2 million years. [1]](/f/9ff13dde2c3a54be9f24c86ea3651eba.jpg)
O rubidium occurs naturally as two isotopes., O 85Rb, which is stable, and the 87Rb, radioactive, with time to half life of 48.8 billion years. This again gives the clock function to this isotope, but a geological clock. O 87Rb undergoes radioactive decay to the isotope 87Sr, which is stable, so you can compare the amounts of 87Rb and 87Sr with the naturally occurring isotope 86Sr for rock dating.
Because it ionizes easily, rubidium has been considered for use in ion engines in spacecraft, a ion thruster system, much more economical than conventional thrusters, and can make rockets more light. The RbAg compound4I5 has also been shown to be important, as it is currently the ionic crystal with the highest conductivity ambient conditions, which puts it in the position of being used in thin-film batteries.
Rubidium carbonate is used to reduce the electrical conductivity of materials, which improves the stability and durability of fiber optic telecommunication networks. Rubidium chloride can be used to treat depression. In other applications, rubidium hydroxide can also be used in making fireworks to oxidize other elements and thus produce violet tones.
Read too: Tellurium - chemical element with chemistry similar to sulfur
What precautions should be taken with rubidium?
There are no known problems caused to human health as a result of exposure to natural rubidium, and its use has little environmental impact.
However, as previously mentioned, the handling of rubidium in metallic form must be carried out cautiously, since it can spontaneously ignite when it comes into contact with air. Your reaction with water is also very explosive, therefore, controlled amounts of rubidium must be used in the experiments.
solved exercises
Question 1 — (UFU/2008)
To determine the age of Earth and rocks, scientists use radioisotopes with very long half-lives, such as Uranium-238 and Rubidium-87. In the radioactive decay of Rubidium-87 there is emission of a negative beta particle.
In this case, the formed element has
(A) 49 protons and 38 neutrons.
(B) 37 protons and 50 neutrons.
(C) 39 protons and 48 neutrons.
(D) 38 protons and 49 neutrons.
Resolution
The question states that, in the decay of rubidium-87, there is the emission of a negative beta particle, which is an electron ejected from the nucleus from the disintegration of a neutron and therefore it is represented as -1β0, that is, with charge -1 and negligible mass, just like the electron. The radioactive decay reaction is as follows:
37Rb87 → -1β0 + TheXB
Being The the atomic number of the formed element and B the mass number of the formed element.
So, we can say that:
37 = -1 + a; hence, a = 38;
87 = 0 + b; hence, b = 87.
We are dictating an element of atomic number 38 and mass number 87. As the number of neutrons can be established by the formula A = Z + n, the calculation is done:
87 = 38 + n; therefore n = 49
Therefore, the element formed has 38 protons and 49 electrons.
Question 2 — (IFGO/2012)
Rubidium is an alkali metal, which has a shiny silvery white color that quickly fades in contact with air. Silicon is the second most abundant element in the Earth's crust. Rubidium can be used in photoelectric cells and silicon in the manufacture of microelectronic devices.
Comparing these two elements, it is correct to state that:
(A) silicon has a larger atomic radius.
(B) silicon has greater electron affinity.
(C) rubidium has higher ionization energy.
(D) silicon is less electronegative.
(E) rubidium is less likely to lose electrons.
Resolution
O silicon is a nonmetal of family 14, being in the third period of the periodic table. Rubidium is an alkali metal from the fifth period of the periodic table.
Therefore, rubidium has a greater atomic radius than silicon, since the longer the period, the greater the number of electronic layers and, thus, the greater the atomic radius, which invalidates alternative A.
THE ionization energy is the energy required to remove a valence electron from an isolated atom in the gaseous state, that is, it has to do with the ease of removing valence electrons from a given element. Rubidium, as an alkali metal, of 5s sublevel1, has a greater tendency to lose electrons; therefore, a lower ionization energy, a classic property of metals, inclusive. Therefore, alternatives C and E cannot be correct.
Silicon is no less electronegative than rubidium, as silicon is a kind of smaller atomic radius, and elements of smaller atomic radius have greater electronegativity, so the letter D cannot be correct.
Thus, the template is the letter B, since in fact silicon has greater electronic affinity, which is the energy released or absorbed by an atom when it receives an electron in its valence layer. When the process is favorable, energy is released and electron affinity is higher, otherwise energy is absorbed and electron affinity is lower. Since rubidium has a greater tendency to lose electrons, it cannot have a greater electron affinity than silicon.
Image credits
[1] geogif / Shutterstock.com
By Stéfano Araújo Novais
Chemistry teacher
