Chemical characteristics of argon. Argon is a special element of the periodic table

DEFINITION

Argon- the eighteenth element of the periodic table. Designation - Ar from the Latin "argon". Located in the third period, VIIIA group. Belongs to the group of noble (inert) gases. The nuclear charge is 18.

The most common group VIIIA element in nature. The argon content in the air is 0.932% (vol.), 1.28% (mass).

It is a colorless gas. It is poorly soluble in water (solubility decreases in the presence of strong electrolytes), better in organic solvents. Forms a clathrate of composition 8Ar×46H 2 O. Does not react with all other substances (simple and complex).

Atomic and molecular mass of argon

DEFINITION

Relative molecular mass of the substance (Mr) is a number showing how many times the mass of a given molecule is greater than 1/12 the mass of a carbon atom, and relative atomic mass of an element(A r) - how many times the average mass of atoms of a chemical element is greater than 1/12 of the mass of a carbon atom.

Since in the free state argon exists in the form of monatomic Ar molecules, the values of its atomic and molecular masses coincide. They are equal to 39.948.

Argon isotopes

It is known that in nature argon can be found in the form of three stable isotopes 36 Ar (0.337%), 38 Ar (0.063%) and 40 Ar (99.6%). Their mass numbers are 36, 38 and 40, respectively. The nucleus of an atom of the argon isotope 36 Ar contains eighteen protons and eighteen neutrons, and the isotopes 38 Ar and 40 Ar contain the same number of protons, twenty and twenty-two neutrons/a, respectively.

There are artificial isotopes of argon with mass numbers from 32 to 55, among which the most stable is 39 Ar with a half-life of 269 years.

Argon ions

Like helium and neon, when the atoms are strongly excited, argon forms molecular ions of the Ar 2 + type.

Argon molecule and atom

In the free state, argon exists in the form of monatomic Ar molecules.

Examples of problem solving

EXAMPLE 1

ARGON, Ar (lat. Argon * a. argon; n. Argon; f. argon; i. argon), is a chemical element of the main subgroup of group VIII of the periodic system, belongs to the inert gases, atomic number 18, atomic mass 39.948. It consists of three stable isotopes, the main one is 40 Ar (99.600%). Isolated from the air in 1894 by English scientists J. Rayleigh and W. Ramsay.

Argon in nature

In nature, argon exists only in free form. Under normal conditions, argon is a colorless, odorless, and tasteless gas. Solid argon crystallizes into cubic argon. argon 1.78 kg/m3, melting point - 189.3°C, boiling point - 185.9°C, critical pressure 48 MPa, critical temperature - 122.44°C. The first ionization potential is 15.69 eV. Atomic radius 0.188 nm (1.88E).

Properties of argon

No chemical compounds have been obtained (only inclusion compounds are known). Under normal conditions, 51.9 cm 3 of argon dissolves in 1 liter of distilled water. Forms crystalline hydrates of the Ar type. 6H 2 O. Weight clarke in the earth's crust 4. 10 -4 ; content in the atmosphere is 0.9325 volume % (6.5 - 10 16 kg), in igneous rocks 2.2. 10 -5 cm 3 /g, in ocean water 0.336 cm 3 /l. 5.3 was produced in the mantle. 10 19 kg 40 Ar, the average rate of accumulation of 40 Ar in the earth's crust is 2 .10 7 kg/year.

From minerals, argon atoms migrate along dislocations to zones of disruption of the crystal structure and then enter oil and gas deposits through microcracks and pores. The method for determining the age of geological objects is based on measuring the ratio of 40 Ar/40 K contents in potassium-containing minerals. The argon method is used to determine the ages of igneous (from micas, amphiboles), sedimentary (from glauconites, sylvites), metamorphosed rocks, for which the age is also given with a known approximation. An activation dating method has been developed, based on measuring the 40 Ar/ 39 Ar ratio.

Production and use of argon

In industry, argon is produced through the process of air separation with deep cooling. It is possible to obtain argon from the purge gases of ammonia synthesis columns. The separation of argon from other inert gases is most completely carried out by the gas chromatographic method.

Argon is used in the heat treatment of easily oxidized metals. In a protective atmosphere of argon, welding and cutting of rare and non-ferrous metals, smelting, etc. are carried out, and crystals of semiconductor materials are grown. The radioactive isotope (37 Ar) is used to control ventilation systems.

Translated from Greek, "argon" means "slow" or "inactive." This definition argon gas received due to its inert properties, allowing it to be widely used for many industrial and domestic purposes.

Chemical element Ar

Ar– 18th element of the periodic table, belonging to the noble inert gases. This substance is the third after N (nitrogen) and O (oxygen) in terms of content in the Earth's atmosphere. Under normal conditions, it is colorless, non-flammable, non-toxic, tasteless and odorless.

Other properties of argon gas:

atomic mass: 39.95;
content in air: 0.9% volume and 1.3% mass;
density under normal conditions: 1.78 kg/m³;
boiling point: -186°C.

The picture shows the name of the chemical element and its properties.

This element was discovered by John Strett and William Ramsay while studying the composition of air. The discrepancy in density in various chemical tests led scientists to believe that in addition to nitrogen and oxygen, there was an inert heavy gas in the atmosphere. As a result, in 1894, a statement was made about the discovery of a chemical element, the proportion of which in each cubic meter of air is 15 g.

How is argon produced?

Ar does not change during its use and always returns to the atmosphere. Therefore, scientists consider this source to be inexhaustible. It is extracted as a by-product when air is separated into oxygen and nitrogen through low-temperature rectification.

To implement this method, special air separation devices are used, consisting of high- and low-pressure columns and a condenser-evaporator. As a result of the rectification (separation) process, argon with small impurities (3-10%) of nitrogen and oxygen is obtained. To perform purification, impurities are removed using additional chemical reactions. Modern technologies make it possible to achieve 99.99% purity of this product.

Installations for the production of this chemical element are presented

Argon gas is stored and transported in steel cylinders (GOST 949-73), which are gray in color with a stripe and a corresponding green inscription. In this case, the process of filling the container must fully comply with technological standards and safety rules. Detailed information about the specifics of filling gas cylinders can be read in the article: cylinders with welding mixture - technical features and operating rules.

Where is argon gas used?

This element has a fairly wide scope of application. Below are the main areas of its use:

filling the internal cavity of incandescent lamps and double-glazed windows;
displacement of moisture and oxygen for long-term storage of food products;
extinguishing agent in some fire extinguishing systems;
protective environment during the welding process;
plasma-forming gas for plasma welding and cutting.

In welding production, it is used as a protective medium in the process of welding rare metals (niobium, titanium, zirconium) and their alloys, alloyed steels of various grades, as well as aluminum, magnesium and chromium-nickel alloys. For ferrous metals, as a rule, a mixture of Ar with other gases is used - helium, oxygen, carbon dioxide and hydrogen.

Type of protective environment during the welding process created by argon

Precautions for use

This chemical element poses absolutely no danger to the environment, but at high concentrations it has a suffocating effect on humans. It often accumulates near the floor in insufficiently ventilated areas, and if the oxygen content decreases significantly, it can lead to loss of consciousness and even death. Therefore, it is important to monitor the oxygen concentration indoors, which should not fall below 19%.

Liquid Ar can cause frostbite in areas of the skin and damage the mucous membrane of the eyes, so it is important to use protective clothing and safety glasses when working. When working in an atmosphere of this gas, in order to prevent suffocation, it is necessary to use an insulating oxygen device or a hose gas mask.

We all know that argon is used for welding various metals, but not everyone has thought about what this chemical element is. Meanwhile, its history is rich in events. What is characteristic is that argon is an exceptional instance of the periodic table of Mendeleev, which has no analogues. The scientist himself wondered at one time how he could even get here.

About 0.9% of this gas is present in the atmosphere. Like nitrogen, it is neutral, colorless and odorless. It is not suitable for maintaining life, but it is simply irreplaceable in some areas of human activity.

A short excursion into history

It was first discovered by an Englishman and physicist by training, G. Cavendish, who noticed the presence in the air of something new, resistant to chemical attack. Unfortunately, Cavendish never learned the nature of the new gas. A little over a hundred years later, another scientist, John William Strat, noticed this. He came to the conclusion that there was some admixture of gas of unknown origin in the nitrogen from the air, but he could not yet understand whether it was argon or something else.

At the same time, the gas did not react with various metals, chlorine, acids, and alkalis. That is, from a chemical point of view, it was inert in nature. Another surprise was the discovery that the molecule of the new gas contains only one atom. And at that time, such a composition of gases was still unknown.

The public announcement of the new gas shocked many scientists from all over the world - how could a new gas in the air be overlooked during many scientific studies and experiments?! But not all scientists, including Mendeleev, believed in the discovery. Judging by the atomic mass of the new gas (39.9), it should be located between potassium (39.1) and calcium (40.1), but the position has already been taken.

As already mentioned, argon has a rich and detective history. For some time it was forgotten, but after the discovery of helium, the new gas was officially recognized. It was decided to allocate a separate zero position for it, located between the halogens and alkali metals.

Properties

Among other inert gases that are included in the heavy group, argon is considered the lightest. Its mass exceeds the weight of air by 1.38 times. The gas turns into a liquid state at a temperature of -185.9 °C, and at -189.4 °C and normal pressure it solidifies.

Argon differs from helium and neon in that it can dissolve in water - at a temperature of 20 degrees in the amount of 3.3 ml per hundred grams of liquid. But in a number of organic solutions the gas dissolves better. Exposure to electric current causes it to glow, which is why it has become widely used in lighting equipment.

Biologists have discovered another useful property that argon has. This is a kind of environment where the plant feels great, as proven by experiments. So, being in a gas atmosphere, the planted seeds of rice, corn, cucumbers and rye sprouted. In another atmosphere, where 98% is argon and 2% is oxygen, vegetables such as carrots, lettuce and onions germinate well.

What is especially characteristic is that the content of this gas in the earth’s crust is much greater than that of other elements found in its group. Its approximate content is 0.04 g per ton. This is 14 times the amount of helium and 57 times the amount of neon. As for the Universe around us, there is even more of it, especially on different stars and in nebulae. According to some estimates, there is more argon in the vastness of space than chlorine, phosphorus, calcium or potassium, which is abundant on Earth.

Receiving gas

The argon in cylinders in which we most often find it is an inexhaustible source. In addition, in any case, it returns to the atmosphere due to the fact that it does not change physically or chemically when used. An exception may be cases where a small amount of argon isotopes is consumed to obtain new isotopes and elements during nuclear reactions.

In industry, gas is produced by separating air into oxygen and nitrogen. As a result, gas is created as a by-product. For this purpose, special industrial double rectification equipment is used with two high and low pressure columns and an intermediate condenser-evaporator. In addition, ammonia production waste can be used to produce argon.

Application area

The scope of application of argon includes several areas:

food industry;
metallurgy;
scientific research and experiments;
welding work;
electronics;
Automotive industry.

This neutral gas is found inside the electric paws, which slows down the evaporation of the tungsten coil inside. Due to this property, welding machines based on this gas are widely used. Argon allows you to reliably connect parts made of aluminum and duralumin.

The gas became widespread when creating a protective and inert atmosphere. This is usually necessary for heat treatment of those metals that are easily susceptible to oxidation. Crystals grow well in an argon atmosphere to produce semiconductor elements or ultrapure materials.

Advantages and disadvantages of using argon in welding

Regarding the welding area, argon offers certain advantages. First of all, metal parts do not heat up as much during welding. This avoids deformation. Other advantages include:

reliable protection of the weld seam;
the speed is an order of magnitude higher;
the process is easy to control;
welding can be mechanized or completely transferred to automatic mode;
the ability to connect parts made of dissimilar metals.

At the same time, argon welding also implies a number of disadvantages:

When welding, ultraviolet radiation occurs;
to use a high-ampere arc, high-quality cooling is necessary;
difficult work outdoors or in drafts.

However, with so many advantages, it is difficult to underestimate the importance of argon welding.

Precautionary measures

Caution should be exercised when using argon. Although the gas is non-toxic, it can cause suffocation by replacing oxygen or liquefying it. Therefore, it is extremely important to control the volume of O 2 in the air (at least 19%) using special devices, manual or automatic.

Working with liquid gas requires extreme caution, since the low temperature of argon can cause severe frostbite of the skin and damage to the eye shell. It is necessary to use glasses and protective clothing. Persons who need to work in an argon atmosphere must wear gas masks or other insulating oxygen devices.

Appearance of a simple substance
An inert gas without color, taste or smell
Properties of the atom
Name, symbol, number	Argon / Argon (Ar), 18
Atomic mass (molar mass)	39.948 a. e.m. (g/mol)
Electronic configuration	3s 2 3p 6
Atomic radius	71pm
Chemical properties
Covalent radius	106 pm
Ion radius	154 pm
Electronegativity	4.3 (Pauling scale)
Electrode potential	0
Oxidation states	0
Ionization energy (first electron)	1519.6(15.75) kJ/mol (eV)
Thermodynamic properties of a simple substance
Density (at normal conditions)	(at 186 °C) 1.40 g/cm 3
Melting temperature	83.8K
Boiling temperature	87.3K
Heat of vaporization	6.52 kJ/mol
Molar heat capacity	20.79 J/(K mol)
Molar volume	24.2 cm 3 /mol
Crystal lattice of a simple substance
Lattice structure	cubic face-centered
Lattice parameters	5.260 A
Debye temperature	85K
Other characteristics
Thermal conductivity	(300 K) 0.0177 W/(m K)

The history of the discovery of 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 in them, 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 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.

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.%). It was too incredible that several generations of scientists did not notice the component of air, and even in the amount of a whole percent! 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.

Main Application

Food industry

In a controlled environment, argon can be used as a replacement for nitrogen in many processes. High solubility (twice the solubility of nitrogen) and certain molecular characteristics provide its special properties for storing vegetables. Under certain conditions, it can slow down metabolic reactions and significantly reduce gas exchange.

Production of glass, cement and lime

When used to fill double-glazed fences, argon provides excellent thermal insulation.

Metallurgy

Argon is used to prevent contact and subsequent interaction between the molten metal and the surrounding atmosphere.

The use of argon allows optimization of such production processes as mixing of molten substances, purging of reactor trays to prevent re-oxidation of steel and processing of narrow-purpose steel in vacuum degassers, including vacuum-oxygen decarburization, redox processes and open combustion processes. However, argon has gained the greatest popularity in the processes of argon-oxygen decarburization of unrefined high-chromium steel, allowing the oxidation of chromium to be minimized.

Laboratory research and analysis

In its pure form and in combination with other gases, argon is used for industrial and medical analysis and quality control testing.

Specifically, argon functions as a gas plasma in inductively coupled plasma (ICP) emission spectrometry, a cushion gas in graphite furnace atomic absorption spectroscopy (GFAAS), and a carrier gas in gas chromatography using various gas analyzers.

Combined with methane, argon is used in Geiger counters and X-ray fluorescence (XRF) detectors, where it acts as a quenching gas.

Welding, cutting and coating

Argon is used as a shielding medium in arc welding processes, shielding gas injection, and plasma cutting.

Argon prevents oxidation of welds and reduces the amount of smoke emitted during the welding process.

Electronics

Ultrapure argon serves as a carrier gas for chemically active molecules, and also as an inert gas to protect semiconductors from foreign impurities (for example, argon provides the necessary environment for growing silicone and germanium crystals).

In its ionic state, argon is used in sputter metallization, ion implantation, normalization, and etching processes in semiconductor and high-performance materials manufacturing.

Automotive and transport industry

Contained sealed argon is used to fill airbags in cars.