On our planet there are many different compounds, organic and mineral substances. So, over one and a half million structures from the world of organic matter and more than 500 thousand outside of it are openly, synthesized and used by man. And every year this figure is growing, since the development of the chemical industry does not stand still, the countries of the world are actively developing and promoting it.
But not even that is surprising. And the fact that all this variety of substances is built of only 118 chemical elements. This is really great! The periodic system of chemical elements is the basis that graphically reflects the diversity of the organic and inorganic world.
Classification of chemical elements
There are several options for gradation of these structures. So, the periodic table for chemistry is conditionally divided into two groups:
- metal elements (most)
- non-metals (smaller part).
In this case, the first consists of elements that are below the conditional diagonal border from boron to astatine, and the second - those that are higher. However, there are exceptions to this classification, for example, tin (exists in alpha and beta form, one of which is metal and the other non-metal). Therefore, this division option cannot be called absolutely fair.
Also, a periodic system of chemical elements can be classified according to the properties of the latter.
- Having the main properties (reducing agents) - typical metals, elements of 1.2 groups of the main subgroups (except for beryllium).
- Possessing acidic properties (oxidizing agents) are typical non-metals. Elements of 6.7 groups of main subgroups.
- Amphoteric properties (dual) - all metals of the subgroups and some of the main ones.
- Non-metal elements that manifest themselves both as reducing agents and as oxidizing agents (depending on the reaction conditions).
More often this is how chemical elements are studied. The 8th grade of the school involves the initial study of all structures with the memorization of the symbol, name and pronunciation in Russian. This is a prerequisite for the competent mastery of chemistry in the future, the basis of everything. The periodic table for chemistry is always in the field of view of children, but you should still know the most common and chemically active ones.
A special group in this system is the eighth in a row. Its elements of the main subgroup are called inert - noble - gases for their completed electron shells and, as a result, low chemical activity. One of them - krypton, a chemical element at number 36 - will be considered in more detail by us. The rest of his brothers in the table are also noble gases and are used by man very widely.
Krypton is a chemical element.
This inhabitant of the Periodic system is located in the fourth period, the eighth group, the main subgroup. The serial number, and hence the number of electrons, and the charge of the nucleus (number of protons) = 36. From this we can conclude what the electronic formula of krypton will be. We write it: + 36 Kr 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 6 .
Obviously, the external energy level of the atom is completely completed. This determines the very low chemical activity of this element. Nevertheless, under certain conditions, it is still possible to force a stable gas such as krypton to enter into some reactions. A chemical element, or rather, its position in the system, electronic structure, allows one more important characteristic of the atom to be obtained: valency. That is the ability to form chemical bonds.
Usually we say that it is almost always equal to the number of the group in which it is located for the unexcited state of atoms (if you count it from first to fourth in order, and then vice versa, 1234321). However, the valency of krypton does not fit into this framework, since without additional energy, that is, without excitation of the atom, it is generally completely inert and its valency is zero.
If, nevertheless, the atom is excited, then the electrons can pair up and move to the free 4d orbital. Hence the possible valencies of krypton: 2,4,6. The oxidation states are corresponding with the + sign (+ 2, + 4, + 6).
Discovery story
After the discovery of inert gases - argon in 1894, helium in 1985 - it was not difficult for scientists to predict and confirm the possibility of the existence of other similar gases in nature. The main efforts along this path were made by W. Ramsay, who discovered argon. He rightly believed that there were still inert gases in the air, but their amount was so insignificant that technology could not record their presence.
Therefore, the krypton element was discovered only after a few years. In 1898, neon gas was released from the air, and followed by another inert compound, which it was decided to call krypton for the difficulty of finding and isolating. Indeed, translated from Greek "cryptos" means hidden.
It was not possible to detect him for a long time, it was very difficult. This fact is confirmed by the fact that one milliliter of gas is contained in one cubic meter of air. That is, the volume is less than a thimble! In order to be able to study the substance, it took one hundred cubic centimeters of liquid air. Fortunately, it was during this period that scientists were able to develop methods for obtaining and liquefying air in large quantities. This turn of the matter made it possible for W. Ramsay to succeed in discovering the element of krypton.
Spectroscopy data confirmed preliminary conclusions about the new substance. Hidden gas has completely new lines in the spectrum, which were not present in any compound at that time.
Simple substance formed and its formula
If krypton is a chemical element related to inert gases, it is logical to assume that its simple substance will be a volatile molecule. And there is. The simple substance of krypton is a monatomic gas with the formula Kr. Usually we are used to seeing gases with an index of "2", for example, O 2 , H 2 and so on. But this element is different due to its belonging to the family of noble gases and the completed electron shell of the atom.
Physical properties
Like any other compound, this one also has its own characteristics. The physical properties of krypton are as follows.
- Very heavy gas - three times superior to air.
- It has no taste.
- Colorless.
- It is odorless.
- Boiling point -152 0 .
- The density of the substance under ordinary conditions is 3.74 g / l.
- Melting point -157.3 0 .
- The ionization energy is high, amounting to 14 eV.
- Electronegativity is also quite large - 2.6.
- Soluble in benzene, slightly in water. With increasing temperature, the solubility decreases. Also miscible with ethanol.
- At room temperature it has a dielectric constant.
Thus, the krypton gas has a sufficient number of characteristics to enter into chemical reactions and be useful to a person for its properties.
Chemical properties
If you transfer krypton (gas) to a solid state, then it crystallizes into a spatial face-centric cubic lattice. In this state, he is also able to enter into chemical reactions. They are very few, but still exist.
There are several types of substances that have been obtained on the basis of krypton.
1. Forms clathrates with water: Kr . 5.75H 2 O.
2. Forms them with organic matter:
- 2.14Kr . 12C 6 H, OH;
- 2.14Kr . 12C 6 H 5 CH 3;
- 2Kr . CCl 4 . 17H 2 O;
- 2Kr . CHCL 3 . 17H 2 O;
- 2Kr . (CH 3 ) 2 CO . 17H 2 O;
- 0.75 Kr . CS 6 H 4 (OH) 2.
3. Under severe conditions, it is able to react with fluorine, that is, oxidize. Thus, the krypton formula with the reagent takes the form: KrF 2, or krypton difluoride. The oxidation state in the compound is +2.
4. More recently, they managed to synthesize a compound that includes bonds between krypton and oxygen: Kr-O (Kr (OTeF 5 ) 2 ).
5. In Finland, they obtained an interesting compound of krypton with acetylene called hydrocryptoacetylene: HKrC≡CH.
6. Krypton fluoride (+4) also exists in KrF 4. When dissolved in water, this compound is able to form weak and unstable kryptonic acid, from which only barium salts are known: BaKrO 4 .
7. The formula of krypton in compounds produced from its difluoride looks like this:
- KrF + SbF 6 - ;
- Kr 2 F 3 + AuF 6 - .
Thus, it turns out that, despite the chemical inertness, this gas exhibits reducing properties and is able to enter into chemical interactions under very severe conditions. This gives chemists around the world a green light in exploring the possibilities of the “hidden” air component. It is possible that soon new compounds will be synthesized, which will find wide application in engineering and industry.
Gas detection
There are several main ways to determine this gas:
- chromatography;
- spectroscopy;
- methods of absorption analysis.
There are several more elements defined by the same methods, they are also placed in the periodic table. Krypton, xenon, radon are the heaviest of noble gases and the most elusive. Therefore, such complex physicochemical methods are required to detect them.
Production methods
The main production method is the processing of liquefied air. But due to the small quantitative content of krypton, it has to process millions of cubic meters in order to produce a small amount of noble gas. In general, the process takes place in three main stages.
- Air treatment on special air separation columns. In this case, the general flow of substances is divided into heavier fractions - a mixture of hydrocarbons and noble gases in liquid oxygen, as well as lighter ones - numerous impurity gases. Since most of the substances are explosive, in the column there is a special outlet pipe through which the heaviest components are immediately separated. Among them is krypton. At the exit, it is heavily contaminated with impurities. In order to obtain the purest product, it is necessary to further subject it to a number of specific chemical treatments with special solvents.
- At this stage, a mixture of krypton and xenon contaminated with hydrocarbons is obtained. For cleaning, special devices are used in which the mixture eliminates most of the unnecessary components by oxidation and adsorption. In this case, the mixture of noble gases itself remains undivided. In addition, the whole process occurs under high pressure, causing the transition of gases into a liquid state.
- At the final stage, separation of the final gas mixture follows with the production of particularly high purity krypton and xenon. For this, a special unique installation has been created, technically perfect for this process. The result is a high quality product in the form of gaseous krypton.
Interestingly, all the described processes can occur cyclically, without stopping production, if the feedstock — air — is supplied with the proper amount. This allows the synthesis of noble gases, including krypton, on a very significant industrial scale.
Storage and transportation of the product is carried out in special metal cylinders with the corresponding inscription. They are under pressure, and their storage temperature does not exceed 20 0 .
Content in nature
In vivo, not just the krypton element is contained, but its isotopes. In total, six varieties that are stable in natural conditions are distinguished:
- krypton-78 - 0.35%;
- krypton-80 - 2.28%;
- krypton-82 - 11.58%;
- krypton-83 - 11.49%;
- krypton-84 - 57%;
- krypton-86 - 17.3%.
Where is this gas contained? Of course, there, from where it was first isolated - in the air. The percentage is very small - only 1.14 * 10 -4 %. Also, the constant replenishment of reserves in nature with this noble gas occurs due to nuclear reactions inside the Earth's lithosphere. It is there that a significant part of the stable isotopic varieties of this element is formed.
Human use
Modern technology allows you to get krypton from the air in large quantities. And there is every reason to believe that it will soon replace inert argon in light bulbs. After all, filled with krypton, they will become more economical: with the same energy consumption, they will last much longer and shine brighter. It is also better to withstand overloads compared to conventional ones that are filled with a mixture of nitrogen and argon.
This can be explained by the inactivity of large and heavy krypton molecules, which slow down the transfer of heat from the glass of the bulb to the filament and reduce the evaporation of atoms of the substance from its surface.
Also, the radioactive isotope of krypton 85 Kr is used to fill special lamps, as it is able to emit beta rays. This radiation energy turns into visible light. Such lamps consist of a glass cylinder, the inner walls of which are coated with a phosphorescent compound. The beta rays of the krypton isotope, falling on this layer, cause its glow, which is perfectly noticeable even at a distance of 500 m.
At a distance of up to 3 meters, even printed text can be clearly seen. The lamps are durable because the half-life of the krypton 85 isotope is about 10 years. Devices work regardless of the current source and external conditions.
Krypton fluorides are also used as oxidizing agents for rocket fuel. Compound Kr-F is used in the manufacture of excimer lasers. Some krypton isotopes are used in medicine. Mainly for equipment diagnostics, detection of perforations and leaks in vacuum installations, prediction and detection of corrosion, as a control over the wear of equipment parts.
Another option for using krypton is the x-ray tubes that are filled with it. Modern scientists are looking for ways to use this gas as a filler in the composition of breathing mixtures for immersion in water. Its use as an anesthetic in medicine can also be realized.