The argon It is one of the noble gases in the periodic table and constitutes about 1% of the Earth's atmosphere. It is represented by the chemical symbol Ar, an element that has an atomic mass equal to 40 for its most abundant isotope on Earth (40Ar); other isotopes are 36Ar (the most abundant in the Universe), 38Ar and the radioisotope 39Ar.
Its name derives from the Greek word 'argos', which means inactive, slow or idle, since it made up the measurable fraction of the air that did not react. Nitrogen and oxygen react with each other to the heat of an electrical spark, forming nitrogen oxides; carbon dioxide with a basic solution of NaOH; but the Ar, with nothing.
Argon is a colorless gas with no odor or taste. It is one of the few gases that does not show a change of color when condensing, being therefore its colorless liquid like its gas; the same happens with its crystalline solid.
Another of its main characteristics is its emission of violet light when heated inside an electric discharge tube (upper image).
Although it is an inert gas (although not under special conditions), and it also lacks biological activity, it can displace oxygen from the air causing suffocation. Some fire extinguishers actually use this to their advantage to smother the flames by depriving them of oxygen..
Its chemical inertness favors its application as an atmosphere for reactions whose species are susceptible to oxygen, water vapor and nitrogen. It also offers a means to store and manufacture metals, alloys or semiconductors..
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In 1785 Henry Cavendish, while investigating the nitrogen in the air, called “phlogistic air”, concluded that a part of the nitrogen could be an inert component.
More than a century later, in the year 1894, the British scientists Lord Rayleigh and Sir William Ramsey discovered that the nitrogen prepared by the elimination of oxygen from the atmospheric air was 0.5% heavier than the nitrogen obtained from some compounds; for example ammonia.
The researchers suspected the presence of another gas in atmospheric air mixed with nitrogen. Later it was verified that the remaining gas after the elimination of nitrogen from the atmospheric air, was an inert gas that is now known as Argon..
This was the first inert gas isolated on Earth; hence its name, since argon means lazy, inactive. However, as early as 1868 the presence of helium in the sun had been detected by spectroscopic studies.
F. Newall and W. N. Hartley, in 1882, observed emission lines, possibly corresponding to argon, which did not correspond to those of the other known elements.
Argon is a noble gas, and consequently it has the orbitals of its last energy level completely filled; that is, its valence shell has eight electrons. The increase in the number of electrons, however, does not counteract the increasing force of attraction exerted by the nucleus; and therefore its atoms are the smallest of each period.
That said, argon atoms can be visualized as "marbles" with highly compressed electron clouds. Electrons move homogeneously through all filled orbitals, making polarization unlikely; that is, a region with a relative electron deficiency originates.
Because of this, the London scattering forces are particularly for argon, and polarization will only benefit if the atomic radius and / or atomic mass increases. That is why argon is a gas that condenses at -186ºC.
By shelling the gas, it will be seen that its atoms or marbles can barely stay together, in the absence of any Ar-Ar covalent bonds. However, it cannot be ignored that such marbles can interact well with other apolar molecules; for example, COtwo, Ntwo, Ne, CH4, all present in the composition of the air.
Argon atoms begin to slow down as the temperature drops to around -186 ° C; then condensation happens. Now the intermolecular forces acquire greater effectiveness, because the distance between the atoms is smaller, and gives time for the few instantaneous dipoles or polarizations to occur..
This liquid argon is messy and it is unknown how exactly its atoms might be arranged..
As the temperature drops further, down to -189ºC (just three degrees lower), the argon begins to crystallize into colorless ice (lower image). Perhaps thermodynamically ice is more stable than argon ice.
In this ice or argon crystal, its atoms do adopt an ordered face-centered cubic (fcc) structure. Such is the effect of their weak interactions at these temperatures. In addition to this structure, it can also form hexagonal crystals, more compact.
Hexagonal crystals are favored when argon crystallizes in the presence of small amounts of Otwo, Ntwo and CO. When deformed they transition to the face-centered cubic phase, the most stable structure for solid argon.
The electron configuration for argon is:
[Ne] 3stwo3p6
Which is the same for all isotopes. Note that its valence octet is complete: 2 electrons in the 3s orbital, and 6 in the 3p orbital, adding 8 electrons in total..
Theoretically and experimentally, argon can use its 3d orbitals to form covalent bonds; but high pressure is required to "force" it.
It is a colorless gas that when exposed to an electric field acquires a lilac-violet glow.
39.79 g / mol
18
83.81 K (-189.34 ºC, -308.81 ºF)
87,302 K (-185,848 ºC, -302,526 ºF)
1,784 g / L
1.38 (relative to air taken as 1).
33.6 cm3/ kg. If argon as a very cold liquefied gas comes into contact with water, violent boiling occurs.
Soluble.
1.18 kJ / mol
8.53 kJ / mol
Log P = 0.94
First level: 1,520.6 kJ / mol
Second level: 2,665.8 kJ / mol
Third level: 3,931 kJ / mol
That is, the energies necessary to obtain the cations between Ar+ and Ar3+ gas phase.
Argon is a noble gas, and therefore its reactivity is almost zero. Photolysis of hydrogen fluoride in a solid matrix of argon at a temperature of 7.5 K (very close to absolute zero) produces argon fluorohydride, HArF.
It can be combined with some elements to produce a stable class with beta-hydroquinone. In addition, it can form compounds with highly electromagnetic elements, such as O, F, and Cl..
Most of the applications of argon are based on the fact that being an inert gas, it can be used to establish an environment to develop a set of industrial activities.
-Argon is used to create an environment for arc welding metals, avoiding the damaging action that the presence of oxygen and nitrogen can produce. It is also used as a covering agent in the refinement of metals such as titanium and zirconium..
-Incandescent light bulbs are usually filled with argon, to protect their filaments and extend their life. It is also used in fluorescent tubes similar to neon ones; but, they emit a blue-purplish light.
-It is used in the decarburization process of stainless steel and as a propellant gas in aerosols.
-Used in ionization chambers and particle counters.
-Also in the use of different elements for the doping of semiconductors.
-It allows creating an atmosphere for the growth of silicon and germanium crystals, widely used in the field of electronics.
-Its low thermal conductivity is beneficial to be used as an insulator between the glass sheets of some windows.
-It is used to preserve food and other materials subjected to packaging, since it protects them from oxygen and moisture that can have a damaging effect on the content of the packaging.
-Argon is used in cryosurgery to remove cancerous tissues. In this case, argon behaves like a cryogenic liquid.
-It is used in medical laser equipment to correct various eye defects, such as: bleeding in blood vessels, retinal detachment, glaucoma, and degeneration of the macula.
-Argon is used in mixtures with helium and neon in Geiger radioactivity counters..
-It is used as a carrier gas in gas chromatography.
-Disperses materials that coat the sample under scanning electron microscopy.
Argon is found as part of the atmospheric air, constituting about 1% of the atmospheric mass. The atmosphere is the main industrial source for the insulation of this gas. Isolated by cryogenic fractional distillation procedure.
On the other hand, in the Cosmos the stars generate enormous amounts of argon during the nuclear fusion of silicon. It can also be located in the atmospheres of other planets, such as Venus and Mars..
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