Argon, properties of the atom, chemical and physical properties

Argon is a noble gas. The noble gases are the 7 elements in group 18 (VIII A) of the periodic table (The periodic table is a diagram that shows how chemical elements are related to each other). Noble gases are also called noble gases because group 18 elements (VIII A) react with very small amounts of other elements. In fact, no argon connection was ever made.

An English chemist named John William Strutt, best known as Lord Rayleigh (1842-1919), chemist William Ramsay (1852-1916) discovered argon in 1894. This was the first noble gas species to be isolated.

Rayleigh and Ramsay discovered argon by fractional distillation of liquid air. Fractional distillation is a method that allows liquid air to be heated slowly. When air is heated, various elements change from liquid back to gas. The portion of air that turns back into gas at -185.86 °C (-302.55 °F) is argon.

Symbol: Ar

Atomic number: 18

Atomic mass: 39.948 a.

Family: Group 18 (VIII A) Noble gas

Pronunciation: AR-gon

Argon is used to make an inert blanket for certain industrial operations. The inert gas envelope prevents any chemicals from reacting when working with oxygen and other small substances present in the air. Argon is also used to create neon lamps and in lasers.

What is Argon, argon, characteristics, properties

Argon is a chemical element Ar,
an element of the 18th group of the periodic table of chemical elements (according to the outdated classification - an element of the main subgroup of group VIII) of the third period of the periodic system of chemical elements of D. I. Mendeleev, with atomic number 18. Denoted by the symbol Ar (lat. Argon ). The third most abundant element in the earth's atmosphere (after nitrogen and oxygen) is 0.93% by volume. The simple substance argon is an inert monatomic gas without color, taste or smell.

Dependence of argon pressure in a cylinder on temperature

As it heats up, the pressure of the gaseous substance in a closed volume increases. The table shows approximate pressure values ​​in the cylinder depending on the ambient temperature.

It should be borne in mind that the balloon pressure does not change instantly, but as it warms up or cools down.

History of the discovery of Argon Argon

The discovery of the element Argon begins in 1785, when the English physicist and chemist Henry Cavendish, studying the composition of air, decided to determine whether all the nitrogen in the air was oxidized. For many weeks, he exposed a mixture of air and oxygen in U-shaped tubes to an electric discharge, as a result of which new portions of brown nitrogen oxides were formed, which the researcher periodically dissolved in alkali. After some time, the formation of oxides stopped, but after binding the remaining oxygen, a gas bubble remained, the volume of which did not decrease with prolonged exposure to electrical discharges in the presence of oxygen. Cavendish estimated the volume of the remaining gas bubble to be 1/120 of the original volume of air. Cavendish could not solve the mystery of the bubble, so he stopped his research and did not even publish its results. Only many years later, the English physicist James Maxwell collected and published Cavendish's unpublished manuscripts and laboratory notes.

The further history of the discovery of argon is associated with the name of Rayleigh, who devoted several years to studying the density of gases, especially nitrogen. It turned out that a liter of nitrogen obtained from the air weighed 1.6 mg more than a liter of “chemical” nitrogen (obtained by decomposing some nitrogenous compound, for example, nitrous oxide, nitrous oxide, ammonia, urea or saltpeter) (the weight of the first was is equal to 1.2521, and the second is 1.2505 g). This difference was not so small that it could be attributed to experimental error. In addition, it was constantly repeated regardless of the source of chemical nitrogen.

Having not come to a solution, in the fall of 1892, Rayleigh published a letter to scientists in the journal Nature, asking for an explanation for the fact that depending on the method of nitrogen release, he received different density values. The letter was read by many scientists, but no one was able to answer the question posed in it.

The already famous English chemist William Ramsay also did not have a ready answer, but he offered Rayleigh his cooperation. Intuition prompted Ramsay to suggest that the nitrogen in the air contains admixtures of an unknown and heavier gas, and Dewar drew Rayleigh’s attention to the description of Cavendish’s ancient experiments (which had already been published by this time).

Trying to isolate a hidden component from thin air, each of the scientists went their own way. Rayleigh repeated Cavendish's experiment on an enlarged scale and at a higher technical level. A transformer energized at 6,000 volts sent a sheaf of electrical sparks into a 50-liter bell filled with nitrogen. A special turbine created a fountain of spray of alkali solution in the bell, absorbing nitrogen oxides and carbon dioxide impurities. Rayleigh dried the remaining gas and passed it through a porcelain tube with heated copper filings, which retained the remaining oxygen. The experiment lasted several days.

Ramsay took advantage of his discovery of the ability of heated magnesium metal to absorb nitrogen, forming solid magnesium nitride. He repeatedly passed several liters of nitrogen through the device he had assembled. After 10 days, the volume of gas stopped decreasing, therefore, all the nitrogen was bound. At the same time, by combining with copper, oxygen, which was present as an impurity in nitrogen, was removed. By this method, Ramsay managed to isolate about 100 cm³ of new gas in his first experiment.

So, a new element was discovered. It became known that it is almost one and a half times heavier than nitrogen and makes up 1/80 of the volume of air. Ramsay, using acoustic measurements, found that the molecule of the new gas consists of one atom - such gases had never been encountered in a stable state before. A very important conclusion followed from this: since the molecule is monatomic, then, obviously, the new gas is not a complex chemical compound, but a simple substance.

Ramsay and Rayleigh spent a lot of time studying its reactivity towards many chemically active substances. But, as one might expect, they came to the conclusion: their gas is completely inactive. It was stunning - until then, no such inert substance had been known.\

Spectral analysis, spectrum of known gases

Spectral analysis played a major role in the study of the new gas. The spectrum of the gas released from the air, with its characteristic orange, blue and green lines, was sharply different from the spectra of already known gases. William Crookes, one of the most prominent spectroscopists of that time, counted almost 200 lines in its spectrum. The level of development of spectral analysis at that time did not make it possible to determine whether the observed spectrum belonged to one or more elements. A few years later, it turned out that Ramsay and Rayleigh were holding in their hands not just one stranger, but several - a whole galaxy of inert gases.

Announcement of the discovery of a new argon gas

On August 7, 1894, in Oxford, at a meeting of the British Association of Physicists, Chemists and Naturalists, a report was made on the discovery of a new element, which was named argon. In his report, Rayleigh stated that in every cubic meter of air there is about 15 g of open gas (1.288 wt.%). The fact that several generations of scientists did not notice the component of air, and even in the amount of a whole percent, was too incredible! In a matter of days, dozens of natural scientists from different countries tested the experiments of Ramsay and Rayleigh. There was no doubt: the air contains argon.

Ten years later, in 1904, Rayleigh received the Nobel Prize in Physics for his studies of the densities of the most common gases and the discovery of argon, and Ramsay received the Nobel Prize in Chemistry for his discovery of various inert gases in the atmosphere.

Application area

Argon is most widely used for welding. It is used to create a protective atmosphere around the weld pool, displacing O2 and N2 contained in the atmosphere from the working area. This is especially important for welding non-ferrous metals, many of which, for example, Ti, are characterized by high chemical activity when heated. Inert gas is also indispensable for permanent connections of stainless and high-alloy alloys.

It is also widely used in the installation of highly loaded building structures, such as frames of high-rise buildings, bridge trusses and many others. Here its use ensures high quality, uniformity and durability of critical connections. In the construction industry, argon welding dominates among other methods.

Argon welding

Argon arc welding

Argon welding is no less widely used in mechanical engineering, primarily in the chemical and food industries. The seams are durable and reliable, even when exposed to aggressive environments.

The oil and gas industries also use argon welding in the installation of pipelines, gas pumping stations and oil refineries.

The method is also used in the nuclear industry, transport engineering and the aerospace industry.

In households, argon welding is not so widespread. This is explained:

• high cost of equipment and consumables;
• the need for sufficient qualification of the welder;
• lower loads experienced by home structures;
• lower requirements for the strength and durability of welded joints.

If a household has an occasional need for such welding work, then it is cheaper, faster and more reliable to invite a specialist welder.

Double-glazed window with argon

The principle of operation of a double-glazed window with argon

A characteristic property of Ar is its higher density compared to air. Therefore, the maximum efficiency of argon welding is achieved in the lower welding position. In this case, the inert substance spreads over the surface of the part and forms a protective cloud of considerable extent, allowing welding to be carried out both with high currents and at high speed. When welding in an inclined and upper position, it is necessary to take into account the “falling through” of argon through the air. To compensate for this phenomenon, either increase the gas supply or carry out work in a sealed room filled with inert gas. In both cases, the cost of work increases.

Since the ionization potential of Ar is low, its use ensures ideal geometric characteristics of the weld, especially the profile. An excited electric arc in an argon atmosphere is also characterized by high stability of its parameters. On the other hand, a low ionization potential also causes a lower arc ignition and maintenance voltage. This reduces its heat generation and complicates the penetration of thick sheets of metal.

The higher arc temperature in an argon atmosphere significantly increases weld penetration. This allows welding to be carried out in one pass, provided that the parameters of the gap between the workpieces are strictly observed.

When using the TIG welding method, the argon atmosphere protects not only the welding zone, but also the end of the infusible electrode from corrosive influences.

In a number of specific cases, helium is added to the protective gas mixture.

In addition to being used for welding, argon is used:

• As a plasma-forming substance in installations for plasma cutting of metal.
• To create an inert environment in food packaging. It displaces air oxygen and water vapor from bags and containers, which adversely affect the shelf life of products. Products in a protective atmosphere are stored several times longer than in conventional packaging. This method is also used for packaging medical products and drugs, allowing them to be kept in proper sterility and chemical purity.
• As an active agent in fire extinguishing installations. Argon displaces oxygen (or other gas) from the combustion site, stopping it.
• To create a protective environment in technological installations when processing semiconductor devices, creating microcircuits and other electronic components or materials of high purity levels.
• Filler for electric lamps.
• In advertising fluorescent tubes.

Chemical properties of Argon Argon

Determination of chemical properties of Argon -

So far, only 2 chemical compounds of argon are known - argon hydrofluoride and CU(Ar)O, which exist at very low temperatures. In addition, argon forms excimer molecules, that is, molecules in which the excited electronic states are stable and the ground state is unstable. There is reason to believe that the extremely unstable Hg-Ar compound formed in an electric discharge is a truly chemical (valence) compound. It is possible that other valence compounds of argon with fluorine and oxygen will be obtained, which should also be extremely unstable. For example, when a mixture of argon and chlorine is electrically excited, a gas-phase reaction is possible with the formation of ArCl. Also, with many substances, between the molecules of which there are hydrogen bonds (water, phenol, hydroquinone and others), it forms inclusion compounds (clathrates), where the argon atom, as a kind of “guest”, is located in the cavity formed in the crystal lattice by the molecules of the substance - host, for example, Ar·6H2O.

The compound CU(Ar)O is obtained from the compound of uranium with carbon and oxygen CUO[9]. The existence of compounds with Ar-Si and Ar-C bonds is likely: FArSiF3 and FArCCH.

Extract:

The noble gas argon can be obtained from liquid air by fractional distillation. Argon can also be produced by heating nitrogen from the atmosphere with hot magnesium or calcium. Magnesium or calcium mixes with nitrogen to form nitride:

A small amount of argon is always present as an admixture with nitrogen gas. It stays behind because it doesn't react with magnesium or calcium.

Argon can also be found in natural gas wells. When natural gas is purified, some argon may be recovered as a byproduct of the reaction.

Interesting Facts

There are a lot of interesting facts related to argon. It’s worth starting with the fact that argon has been banned for use by the international anti-doping company since 2014. The lack of oxygen from inhalation likely activates the body's own erythropoietin (EPO). It is also worth noting that argon at a pressure of about 24 bar can have an analgesic effect. An interesting point is that argon reserves in the atmosphere are replenished on Earth due to solar rays, and in the earth's crust due to underground nuclear explosions.