Chlorine: Characterization of chemical and physical properties

In nature, chlorine is found in the gaseous state and only in the form of compounds with other gases. Under conditions close to normal, it is a toxic, corrosive gas of greenish color. It has more weight than air. Has a sweet smell. The chlorine molecule contains two atoms. In a quiet state it does not burn, but at high temperatures comes into contact with hydrogen, after which an explosion is possible. As a result, gas phosgene is released. It is very toxic. So, even with a low concentration in the air (0.001 mg per 1 dm ³ ) can cause a lethal outcome. The main characteristic of non-metal chlorine is that it is heavier than air, therefore, it will always be at the very floor in the form of a yellowish-green haze.

Historical facts

For the first time in practice, this substance was obtained by K. Shelee in 1774 by combining hydrochloric acid and pyrolusite. However, it was not until 1810 that P. Davy was able to characterize chlorine and establish that it was a separate chemical element.

It is worth noting that in 1772 Joseph Priestley was able to get hydrogen chloride, a chlorine compound with hydrogen, but the chemist could not separate these two elements.

Chemical characterization of chlorine

Chlorine is a chemical element of the main subgroup of the VII group of the periodic table. It is in the third period and has an atomic number of 17 (17 protons in the atomic nucleus). Chemically active non-metal. Denoted by the letters Cl.

It is a typical representative of halogens. These are gases that do not have colors, but have a sharp pungent smell. As a rule, they are toxic. All halogens are well diluted in water. When in contact with moist air, they start to smoke.

The external electron configuration of the atom is Cl 3s2Sp5. Therefore, in compounds, the chemical element exhibits oxidation levels -1, +1, +3, +4, +5, +6 and +7. The covalent radius of the atom is 0.96 Å, the ionic radius of Cl is 1.83 Å, the affinity of the atom for the electron is 3.65 eV, the ionization level is 12.87 eV.

As indicated above, chlorine is a fairly active non-metal, which allows compounds to be formed with virtually any metal (in some cases by heating or by moisture, displacing bromine) and non-metals. In powdered form reacts with metals only under the influence of high temperatures.

The maximum burning temperature is 2250 ° C. With oxygen it is able to form oxides, hypochlorites, chlorites and chlorates. All compounds containing oxygen become explosive under conditions of interaction with oxidizing substances. It is worth noting that chlorine oxides can explode arbitrarily, while chlorates explode only when exposed to them by any initiators.

Characterization of chlorine by position in the periodic system:

• a simple substance;
• element of the seventeenth group of the periodic table;
• the third period of the third row;
• the seventh group of the main subgroup;
• Atomic number 17;
• denoted by the symbol Cl;
• a reactive non-metal;
• is in the halogen group;
• in conditions close to normal, it is a poisonous gas of a yellowish-green color with a pungent smell;
• the chlorine molecule has 2 atoms (formula Cl ₂ ).

Physical properties of chlorine:

• boiling point: -34.04 ° C;
• Melting point: -101.5 ° C;
• density in the gaseous state - 3, 214 g / l;
• the density of liquid chlorine (during the boiling period) is 1.537 g / cm ³ ;
• the density of solid chlorine is 1.9 g / cm ³ ;
• Specific volume - 1,745 x 10 ^-3 l / g.

Chlorine: characteristic of temperature changes

In the gaseous state it is easy to get liquefied. At a pressure of 8 atmospheres and a temperature of 20 ° C it looks like a greenish-yellow liquid. Has very high corrosion properties. As practice shows, this chemical element can maintain a liquid state up to the critical temperature (143 ° C), provided the pressure is increased.

If it is cooled to -32 ° C, it will change its aggregate state to liquid, regardless of atmospheric pressure. With a further decrease in temperature, crystallization occurs (at -101 ° C).

Chlorine in nature

The earth's crust contains only 0.017% of chlorine. The bulk is in volcanic gases. As indicated above, the substance has a high chemical activity, which is why it occurs naturally in compounds with other elements. In this case, many minerals contain chlorine. The characteristic of the element makes it possible to form about one hundred different minerals. As a rule, these are metal chlorides.

Also, a large number of it is in the World Ocean - almost 2%. This is due to the fact that the chlorides are very actively dissolved and carried by rivers and seas. The reverse process is also possible. Chlorine is washed back to the shore, and then the wind carries it around. That is why its greatest concentration is observed in the coastal zones. In the arid regions of the planet, the gas we are considering is formed by the evaporation of water, as a result of which solonchaks appear. Every year in the world produce about 100 million tons of this substance. Which, however, is not surprising, because there are many deposits containing chlorine. Its characteristics, however, largely depend on its geographical location.

Methods for producing chlorine

Today there are a number of methods for obtaining chlorine, of which the most common are:

1. Diaphragmatic. It is the simplest and less expensive. The brine in the diaphragm electrolysis enters the anode space. Further along the steel cathode grid flows into the diaphragm. It contains a small amount of polymer fibers. An important feature of this device is countercurrent. It is directed from the anode space to the cathode, which allows one to separately produce chlorine and liquors.

2. Membrane. The most energy efficient, but difficult to implement in the organization. It is similar to diaphragm. The difference is that the anode and cathode spaces are completely separated by a membrane. Consequently, the output is two separate streams.

It is worth noting that the characteristics of chemical. Element (chlorine) obtained by these methods will be different. More "pure" is considered to be the membrane method.

3. Mercury method with a liquid cathode. Compared with other technologies, this option allows you to get the most pure chlorine.

The basic scheme of the plant consists of an electrolyzer and a pump connected to each other and an amalgam decomposer. As a cathode, mercury is pumped with mercury together with a solution of common salt, and as an anode - carbon or graphite electrodes. The principle of the installation is as follows: chlorine is released from the electrolyte, which is removed from the cell together with the anolyte. From the latter, impurities and chlorine residues are removed, doped with halite and returned to electrolysis.

The requirements of industrial safety and unprofitable production led to the replacement of the liquid cathode with a solid one.

The use of chlorine for industrial purposes

The properties of chlorine make it possible to actively use it in industry. With the help of this chemical element, various organochlorine compounds (vinyl chloride, chloro-rubber, etc.) are obtained, drugs, disinfectants. But the biggest niche in the industry is the production of hydrochloric acid and lime.

Methods of purification of drinking water are widely used. To date, trying to move away from this method, replacing it with ozonation, because the substance we are considering negatively affects the human body, besides chlorinated water destroys the pipelines. This is due to the fact that in the free state Cl adversely affects the pipes made of polyolefins. Nevertheless, most countries prefer the chlorination method.

Also chlorine is used in metallurgy. With its help, a number of rare metals are obtained (niobium, tantalum, titanium). In the chemical industry, various organochlorine compounds are actively used to control weeds and for other agricultural purposes, the element is also used as a bleaching agent.

Due to its chemical structure, chlorine destroys most of the organic and inorganic dyes. This is achieved by completely discolouring them. Such a result is possible only with the presence of water, because the process of decolorization is due to atomic oxygen, which is formed after the disintegration of chlorine: Cl ₂ + H ₂ O → HCl + HClO → 2HCl + O. This method was used a couple of centuries ago and is popular This day.

Very popular application of this substance for the production of organochlorine insecticides. These agricultural preparations kill harmful organisms, leaving the plants untouched. A significant part of all the chlorine produced on the planet goes to agricultural needs.

It is also used in the production of plastic and rubber. With their help, they make insulation of wires, stationery, equipment, shells of household appliances, etc. There is an opinion that rubbers obtained in this way harm a person, but this is not confirmed by science.

It is worth noting that chlorine (a characteristic of the substance was disclosed in detail earlier) and its derivatives, such as mustard gas and phosgene, are also used for military purposes to obtain combat chemical agents.

Chlorine as a bright representative of non-metals

Non-metals are simple substances that include gases and liquids. In most cases, they conduct electric current worse than metals, and have significant differences in physico-mechanical characteristics. With the help of a high level of ionization, it is possible to form covalent chemical compounds. Below, we will give a non-metal characterization using the example of chlorine.

As already mentioned above, this chemical element is a gas. Under normal conditions, it completely lacks properties similar to those of metals. Without external assistance, it can not interact with oxygen, nitrogen, carbon, etc. Its oxidizing properties manifest itself in connections with simple substances and some complex ones. Refers to halogens, which is clearly reflected in its chemical characteristics. In the compounds with the rest of the halogens (bromine, astatine, iodine), they are displaced. In the gaseous state, chlorine (its characteristic is a direct confirmation of this) is readily soluble. It is an excellent disinfectant. It kills only living organisms, which makes it irreplaceable in agriculture and medicine.

Application as a poisonous substance

The characteristic of the chlorine atom makes it possible to use it as a poison. For the first time the gas was used by Germany on 22.04.1915, during the First World War, as a result of which about 15 thousand people died. At the moment, it is not used as a poison .

Let's give a brief description of the chemical element as a suffocating agent. Affects the human body through strangulation. First it irritates the upper respiratory tract and the mucous membrane of the eyes. A violent cough begins with suffocation. Further, penetrating into the lungs, gas corrodes the lung tissue, which leads to edema. Important! Chlorine is a fast-acting substance.

Depending on the concentration in the air, the symptomatology is different. At a small content, the person has reddening of the mucous membrane of the eyes, slight dyspnoea. The content in the atmosphere of 1.5-2 g / m ³ causes severe chest pain, sharp pain in the upper respiratory tract. Also the condition can be accompanied by strong lachrymation. After 10-15 minutes of being in a room with such a concentration of chlorine there is a severe burn of the lungs and death. At denser concentrations, death is possible within a minute of paralysis of the upper respiratory tract.

When working with this substance it is recommended to use overalls, a gas mask, gloves.

Chlorine in the life of organisms and plants

Chlorine is part of almost all living organisms. The peculiarity is that it is present not in pure form, but in the form of compounds.

In animal and human organisms, chloride ions support osmotic equality. This is due to the fact that they have the most suitable radius for penetration into membrane cells. Along with potassium ions, Cl regulates the water-salt balance. In the intestine, chloride ions create a favorable environment for the action of proteolytic enzymes of gastric juice. Chlorine channels are provided in many cells of our body. Through them, intercellular fluid exchange occurs and the pH of the cell is maintained. About 85% of the total volume of this element in the body is in the intercellular space. It is excreted from the body by the urethra. It is produced by the female body in the process of breastfeeding.

At this stage of development, it is difficult to say unambiguously which diseases provoke chlorine and its compounds. This is due to the lack of research in this area.

Chlorine ions are also present in plant cells. He actively participates in the energy exchange. Without this element, the process of photosynthesis is impossible. With its help, the roots actively absorb the necessary substances. But a large concentration of chlorine in plants can have a detrimental effect (slowing down the process of photosynthesis, stopping development and growth).

However, there are representatives of the flora who could "make friends" or at least get along with this element. The characteristic of the non-metal (chlorine) contains such an item as the ability of the substance to oxidize the soil. In the process of evolution, the plants mentioned above, called halophytes, occupied empty solonchaks, which were empty due to the overabundance of this element. They absorb chlorine ions, and then get rid of them with the help of leaf fall.

Transportation and storage of chlorine

There are several ways to move and store chlorine. The characteristic of the element assumes the need for special cylinders with high pressure. Such containers have an identification marking - a vertical green line. Monthly, the cylinders must be thoroughly washed. With prolonged storage of chlorine, a very explosive precipitate is formed in them - nitrogen trichloride. If non-observance of all safety rules, spontaneous ignition and explosion are possible.

Study of chlorine

Future chemists should be aware of the characteristics of chlorine. Under the plan, 9-graders can even put laboratory experiments with this substance on the basis of basic knowledge of the discipline. Naturally, the instructor is obliged to conduct instruction in safety precautions.

The order of work is as follows: you need to take a flask of chlorine and pour in it a small metal shavings. In flight, the chips will flash with bright light sparks and simultaneously a light white smoke of SbCl _{3 is formed} . When immersed in a vessel with chlorine of tin foil, it also spontaneously ignites, and at the bottom of the flask the fiery snowflakes will slowly fall. During this reaction, a smoky liquid - SnCl ₄ - is formed. When the iron shavings are placed in the vessel red "drops" are formed and the red smoke of FeCl ₃ appears.

Along with practical work, the theory is repeated. In particular, such a question as the characterization of chlorine by position in the periodic system (described at the beginning of the article).

As a result of the experiments, it turns out that the element reacts actively to organic compounds. If you put in a jar of chlorine cotton wool soaked beforehand in turpentine, it will immediately ignite, and the soot will fall sharply from the flask. Effectively smoldering yellowish flame sodium, and on the walls of the chemical chamber there are crystals of salt. It will be interesting for the students to learn that while still a young chemist, NN Semenov (later a Nobel Prize winner), having conducted such an experiment, collected salt from the walls of the flask and, having sprinkled bread on it, ate it. Chemistry was right and did not fail the scientist. As a result of the experience of the chemist really got the usual table salt!