DEFINITION

Chlorine is in the third period of the VII group of the main (A) subgroup of the Periodic Table.

Refers to elements of the p-family. Non-metal. The non-metal elements included in this group are collectively called halogens. Designation - Cl. Ordinal number - 17. Relative atomic mass - 35.453 a.m.u.

The electronic structure of the chlorine atom

The chlorine atom consists of a positively charged nucleus (+17), consisting of 17 protons and 18 neutrons, around which 17 electrons move in 3 orbits.

Fig.1. Schematic structure of the chlorine atom.

The distribution of electrons in orbitals is as follows:

17Cl) 2) 8) 7 ;

1s 2 2s 2 2p 6 3s 2 3p 5 .

The outer energy level of the chlorine atom has seven electrons, all of which are considered valence. The energy diagram of the ground state takes the following form:

Having one unpaired electron indicates that chlorine is capable of exhibiting an oxidation state of +1. Several excited states are also possible due to the presence of a vacant 3 d-orbitals. First, electrons are steamed 3 p-sublevels and occupy free d-orbitals, and after - electrons 3 s- sublevel:

This explains the presence of chlorine in three more oxidation states: +3, +5 and +7.

Examples of problem solving

EXAMPLE 1

Exercise	Given two elements with nuclear charges Z=17 and Z=18. The simple substance formed by the first element is a poisonous gas with a pungent odor, and the second is a non-poisonous, odorless, non-respiratory gas. Write the electronic formulas of the atoms of both elements. Which one forms a poisonous gas?
Solution	The electronic formulas of the given elements will be written as follows: 17 Z 1 s 2 2s 2 2p 6 3s 2 3p 5 ; 18 Z 1 s 2 2s 2 2p 6 3s 2 3p 6 . The charge of the nucleus of an atom of a chemical element is equal to its serial number in the Periodic Table. Therefore, it is chlorine and argon. Two chlorine atoms form a molecule of a simple substance - Cl 2, which is a poisonous gas with a pungent odor
Answer	Chlorine and argon.

Introduction………………………………………………………………………………………………3

1. The symbol of the element, its position in the periodic system of elements D.I. Mendeleev. Atomic mass……………………………………………………………………………………….4

2. The structure of the nucleus of the chlorine atom. Possible isotopes. Examples………………………….5

3. Electronic formula of the atom: distribution of electrons by levels, sublevels, Hund cells. The excited state of the chlorine atom…………………………………………………….6

4. Valency of the aluminum atom in the stationary and excited states. Possible oxidation states of the chlorine atom. Redox properties. Examples of electron movement schemes…………………………………………………………………………….8

5. Equivalents of chlorine and its compounds. Calculation examples……………………………..11

6. Chemical properties of chlorine and its compounds. Examples of reactions…………………………………………………12

7. Types of concentrations………………………………………………………………………….15

8. Electrolytic dissociation. Scheme of the hydroxide dissociation process. Dissociation constant………………………………………………………………………………………… 17

9. Calculation of pH, pOH 0.01m solution of hydroxide or salt of an element………………………21

10. Hydrolysis…………………………………………………………………………………..23

11. Qualitative analysis of chlorine………………………………………………………………24

12. Methods for the quantitative determination of the chlorine atom or its compounds……………27

12.1. Gravimetric method for the analysis of the chlorine atom…………………………………………...27

13. Conclusion……………………………………………………………………………….29

References…………………………………………………………………………………32

Introduction

The compound with hydrogen - gaseous hydrogen chloride - was first obtained by Joseph Priestliv in 1772. Chlorine was obtained in 1774 by the Swedish chemist Carl Wilhelm Scheele, who described its release during the interaction of pyrolusite with hydrochloric acid in his treatise on pyrolusite:

Scheele noted the smell of chlorine, similar to the smell of aqua regia, its ability to interact with cinnabar gold, as well as its bleaching properties. However, Scheele, in accordance with the phlogiston theory prevailing in chemistry of that time, suggested that chlorine is a dephlogisticated muriatic (hydrochloric) acid. Bertholley and Lavoisiev, within the framework of the oxygen theory of acids, proved that the new substance should be the oxide of a hypothetical element muria. However, attempts to isolate it remained unsuccessful until the work of Davy, who managed to decompose table salt into sodium chlorine by electrolysis, proving the elemental nature of the latter.

1. The symbol of the element, its position in the periodic system of elements d.I. Mendeleev. Atomic mass

X lor (from the Greek χλωρός - "green") - an element of the 17th group of the periodic table chemical elements(according to the outdated classification - an element of the main subgroup of group VII), of the third period, with atomic number 17. It is denoted by the symbol Cl (lat. Chlorum). Reactive nonmetal. It belongs to the group of halogens (originally, the name "halogen" was used by the German chemist Schweiger for chlorine - literally, "halogen" is translated as salt - but it did not take root and subsequently became common for the 17th (VIIA) group of elements, which includes chlorine).

Simple substance chlorine (CAS number: 7782-50-5) at normal conditions- poisonous gas of a yellowish-green color, heavier than air, with a pungent odor. The chlorine molecule is diatomic (formula Cl2).

Atomic mass

(molar mass)

[comm 1] a. e.m. (g/mol)

2. The structure of the nucleus of the chlorine atom. Possible isotopes. Examples

In nature, there are 2 stable isotopes of chlorine: with a mass number of 35 and 37. The proportions of their content are respectively 75.78% and 24.22%.

Isotope	Relative mass, a.m.u.	Half life	Decay type	nuclear spin
		stable
			β-decay in 36 Ar
		stable
		37.2 minutes	β-decay in 38 Ar
		55.6 minutes	β-decay in 39 Ar
		1.38 minutes	β-decay in 40 Ar

3. Electronic formula of the atom: distribution of electrons by levels, sublevels, Hund cells. Excited state of the chlorine atom

Chlorine in the periodic system of chemical elements is in the 3rd period, group VII, the main subgroup (subgroup of halogens).

The charge of the nucleus of an atom Z = + = + 17

Number of protons N(p+) = 17

Number of electrons N(e-) = 17

In excited state:

1) 3s2 3p5 3d0 + hn --> 3s2 3p4 3d1

3 unpaired electrons (2 electrons on the 3p sublevel and 1 electron on the 3d sublevel), hence the valency is 3

Compound example: HClO2, Cl2O3

2) 3s2 3p4 3d1 + hn --> 3s2 3p3 3d2

5 unpaired electrons (3 electrons on the 3p sublevel and 2 electrons on the 3d sublevel), hence the valency is 5

Compound example: HClO3, Cl2O5

3) 3s2 3p3 3d2 + hn --> 3s1 3p3 3d3

7 unpaired electrons (1 electron in the 3s sublevel, 3 electrons in the 3p sublevel and 3 electrons in the 3d sublevel), hence the valency is 5

4. Valency of the aluminum atom in the stationary and excited states. Possible oxidation states of the chlorine atom. Redox properties. Examples of Electron Movement Schemes

Valence electrons: 3s2 3p5

In the unexcited state, the chlorine atom at the 3rd energy level has one unpaired electron, therefore, an unexcited chlorine atom can exhibit valence 1. Valence 1 appears in the following compounds:

Gaseous chlorine Cl2 (or Сl-Cl)

Sodium chloride NaCl (or Na+ Cl-)

Hydrogen chloride HCl (or H-Cl)

Hypochlorous acid HOCl (or H-O-Cl)

Redox properties.

HCl - oxidation state of chlorine -1

HClO3 - oxidation state of chlorine +5

HClO4 - oxidation state of chlorine +7

An intermediate oxidation state indicates that this element can exhibit both reducing and oxidizing properties, this is HClO3

Oxidizing properties are exhibited by elements that have a maximum oxidation state (it is equal to the number of the group in which the element is located). So HClO4 is an oxidizing agent.

Reducing properties are possessed by an element with a lower degree of oxidation, i.e. HCl is a reducing agent.

Chlorine is a strong oxidizing agent. Various chlorine compounds can be used as oxidizers. These are chlorine C12), hypochlorous acid NSO, salts of hypochlorous acid - sodium hypochlorite NaCIO or calcium hypochlorite Ca (CIO) 2 and chlorine oxide CIO2.

Chlorination is used to remove phenols, cresols, cyanides, hydrogen sulfide from wastewater. To combat biological fouling of structures, it is used as a biocide. Chlorine is also used to disinfect water.

Chlorine enters production in liquid form with a content of at least 99.5%. Chlorine is a highly toxic gas, it has the ability to accumulate and concentrate in small depressions. It is quite difficult to work with him. When released into water, chlorine is hydrolyzed to form hydrochloric acid. With some organic substances that are present in solution, C12 can enter into chlorination reactions. As a result, secondary organochlorine products are formed, which have a high degree of toxicity. Therefore, the use of chlorine tend to limit.

Hypochlorous acid HSO has the same oxidizing power as chlorine. However, its oxidizing properties are manifested only in an acidic environment. In addition, hypochlorous acid is an unstable product - it decomposes over time and in the light.

Hypochlorous acid salts have been widely used. Calcium hypochlorite Ca(CJU)2 is produced in three grades with active chlorine concentration from 32 to 35%. In practice, the dibasic salt Ca(CIO)2-2Ca(OH)g 2H20 is also used.

The most stable sodium hypochlorite salt is NaOCl * 5H20, which is obtained by chemical interaction of gaseous chlorine with an alkali solution or by electrolysis of common salt in a bath without a diaphragm.

Chlorine oxide CO2 is a greenish-yellow gas, highly soluble in water, a strong oxidizing agent. It is obtained by reacting chlorite NaC102 with chlorine, hydrochloric acid or ozone. When chlorine oxide interacts with water, chlorination reactions do not occur, which excludes the formation of organochlorine substances. Recently, extensive research has been carried out to clarify the conditions for replacing chlorine with chlorine oxide as an oxidizing agent. A number of Russian plants have introduced advanced technologies using CO2.

Halogens (from the Greek halos - salt and genes - generative) - elements of the main subgroup VII group of the periodic system: fluorine, chlorine, bromine, iodine, astatine. In the free state, halogens form substances consisting of diatomic molecules F 2, Cl 2, Br 2, I 2. FOUND IN NATURE Halogens are found in nature only in the form of compounds. Fluorine occurs exclusively in the form of salts dispersed in various rocks. The total fluorine content in the earth's crust is 0.02% of atoms. Fluorine minerals are of practical importance: CaF 2 - fluorspar, Na 2 AlF 6 - cryolite, Ca 5 F (PO 4) 3 - fluorapatite. The most important natural compound chlorine is sodium chloride (halite), which serves as the main raw material for the production of other chlorine compounds. The main mass of sodium chloride is found in the water of the seas and oceans. The waters of many lakes also contain a significant amount of NaCl, such as lakes Elton and Baskunchak. There are other chlorine compounds, for example, KCl - sylvin, MgCl 2 *KCl * 6HO - carnallite, KCl * NaCl - sylvinite. Bromine is found in nature in the form of sodium and potassium salts together with chlorine salts, as well as in the water of salt lakes and seas. Metal bromides are found in sea water. In underground drilling waters of industrial importance, the bromine content ranges from 170 to 700 mg/l. The total content of bromine in the earth's crust is 3 * 10-5% of atoms. Connections iodine are present in sea water, but in such small quantities that their direct isolation from water is very difficult. However, there are some algae that accumulate iodine in their tissues, such as kelp. The ash of these algae serves as a raw material for the production of iodine. A significant amount of iodine (from 10 to 50 mg/l) is contained in underground drilling waters. The content of iodine in the earth's crust is 4 * 10-6% of atoms. There are minor deposits of iodine salts - KIO 3 and KIO 4 - in Chile and Bolivia. total weight astatine on the globe, according to estimates, does not exceed 30 years. Table. Electronic structure and some properties of atoms and molecules of halogens

Element symbol	F	Cl	Br	I	At
Serial number
The structure of the outer electronic layer	2s 2 2p 5	3s 2 3p 5	4s 2 4p 5	5s 2 5p 5	6s 2 6p 5
Relative Electro Negativity (EO)	4,0	3,0	2,8	2,5	~2,2
Radius of an atom, nm	0,064	0,099	0,114	0,133	–
Oxidation states	-1	-1, +1, +3, +5, +7	–
State of aggregation	Pale green gas	Green-yellow. gas	brown liquid	Dark violet crystals	black crystals
t°pl.(°C)	-219	-101	-8
t°boiling point (°C)	-183	-34
ρ (g / cm 3)	1,51	1,57	3,14	4,93	–
Solubility in water (g/100g water)	reacts with water	2.5:1 by volume	3,5	0,02	–

1) General electronic configuration of the external energy level- nS 2 nP 5 .

2) With an increase in the ordinal number of elements, the atomic radii increase, electronegativity decreases, non-metallic properties weaken (metallic properties increase); halogens are strong oxidizing agents, the oxidizing power of elements decreases with increasing atomic mass.

3) With an increase in atomic mass, the color becomes darker, the melting and boiling points, as well as the density, increase.

The physical properties of chlorine are considered: the density of chlorine, its thermal conductivity, specific heat capacity and dynamic viscosity at various temperatures. The physical properties of Cl 2 are presented in the form of tables for the liquid, solid and gaseous state of this halogen.

Basic physical properties of chlorine

Chlorine is included in group VII of the third period of the periodic system of elements at number 17. It belongs to the halogen subgroup, has relative atomic and molecular weights of 35.453 and 70.906, respectively. At temperatures above -30°C, chlorine is a greenish-yellow gas with a characteristic pungent, irritating odor. It liquefies easily under ordinary pressure (1.013·10 5 Pa) when cooled to -34°C and forms a clear amber liquid that solidifies at -101°C.

Due to its high reactivity, free chlorine does not occur in nature, but exists only in the form of compounds. It is found mainly in the mineral halite (), it is also part of such minerals as: sylvin (KCl), carnallite (KCl MgCl 2 6H 2 O) and sylvinite (KCl NaCl). The chlorine content in the earth's crust is approaching 0.02% of total number atoms of the earth's crust, where it is in the form of two isotopes 35 Cl and 37 Cl in percentage 75.77% 35Cl and 24.23% 37Cl.

Physical properties of chlorine - table of main indicators

Property	Meaning
Melting point, °С	-100,5
Boiling point, °C	-30,04
Critical temperature, °C	144
Critical pressure, Pa	77.1 10 5
Critical density, kg / m 3	573
Gas density (at 0°С and 1.013 10 5 Pa), kg/m 3	3,214
Density of saturated steam (at 0°С and 3.664 10 5 Pa), kg/m 3	12,08
Density of liquid chlorine (at 0 ° C and 3.664 10 5 Pa), kg / m 3	1468
Density of liquid chlorine (at 15.6 ° C and 6.08 10 5 Pa), kg / m 3	1422
Density of solid chlorine (at -102°С), kg/m 3	1900
Relative density in air of gas (at 0°C and 1.013 10 5 Pa)	2,482
Relative air density of saturated steam (at 0°C and 3.664 10 5 Pa)	9,337
Relative density of liquid chlorine at 0°С (for water at 4°С)	1,468
Specific volume of gas (at 0°С and 1.013 10 5 Pa), m 3 /kg	0,3116
Specific volume of saturated steam (at 0°C and 3.664 10 5 Pa), m 3 /kg	0,0828
Specific volume of liquid chlorine (at 0°C and 3.664 10 5 Pa), m 3 /kg	0,00068
Chlorine vapor pressure at 0°C, Pa	3.664 10 5
Dynamic viscosity of gas at 20°C, 10 -3 Pa s	0,013
Dynamic viscosity of liquid chlorine at 20°C, 10 -3 Pa s	0,345
Melting heat of solid chlorine (at the melting point), kJ/kg	90,3
Heat of vaporization (at boiling point), kJ/kg	288
Heat of sublimation (at melting point), kJ/mol	29,16
Molar heat capacity C p of gas (at -73…5727°C), J/(mol K)	31,7…40,6
Molar heat capacity C p of liquid chlorine (at -101…-34°C), J/(mol K)	67,1…65,7
Gas thermal conductivity coefficient at 0°C, W/(m K)	0,008
Thermal conductivity coefficient of liquid chlorine at 30°C, W/(m K)	0,62
Gas enthalpy, kJ/kg	1,377
Saturated steam enthalpy, kJ/kg	1,306
Enthalpy of liquid chlorine, kJ/kg	0,879
Refractive index at 14°C	1,367
Specific conductivity at -70°C, Sm/m	10 -18
Electron affinity, kJ/mol	357
Ionization energy, kJ/mol	1260

Density of chlorine

Under normal conditions, chlorine is a heavy gas with a density approximately 2.5 times greater than . Density of gaseous and liquid chlorine under normal conditions (at 0 ° C) is equal to 3.214 and 1468 kg / m 3, respectively. When liquid or gaseous chlorine is heated, its density decreases due to an increase in volume due to thermal expansion.

Density of chlorine gas

The table shows the density of chlorine in the gaseous state at various temperatures (in the range from -30 to 140°C) and normal atmospheric pressure (1.013·10 5 Pa). The density of chlorine changes with temperature - when heated, it decreases. For example, at 20 ° C, the density of chlorine is 2.985 kg / m 3, and when the temperature of this gas rises to 100 ° C, the density value decreases to a value of 2.328 kg / m 3.

Density of gaseous chlorine at various temperatures

t, °С	ρ, kg / m 3	t, °С	ρ, kg / m 3
-30	3,722	60	2,616
-20	3,502	70	2,538
-10	3,347	80	2,464
0	3,214	90	2,394
10	3,095	100	2,328
20	2,985	110	2,266
30	2,884	120	2,207
40	2,789	130	2,15
50	2,7	140	2,097

With increasing pressure, the density of chlorine increases. The tables below show the density of gaseous chlorine in the temperature range from -40 to 140°C and pressure from 26.6·10 5 to 213·10 5 Pa. With increasing pressure, the density of chlorine in the gaseous state increases proportionally. For example, an increase in the pressure of chlorine from 53.2·10 5 to 106.4·10 5 Pa at a temperature of 10°C leads to a twofold increase in the density of this gas.

The density of gaseous chlorine at various temperatures and pressures is from 0.26 to 1 atm.

↓ t, °C | P, kPa →	26,6	53,2	79,8	101,3
-40	0,9819	1,996	—	—
-30	0,9402	1,896	2,885	3,722
-20	0,9024	1,815	2,743	3,502
-10	0,8678	1,743	2,629	3,347
0	0,8358	1,678	2,528	3,214
10	0,8061	1,618	2,435	3,095
20	0,7783	1,563	2,35	2,985
30	0,7524	1,509	2,271	2,884
40	0,7282	1,46	2,197	2,789
50	0,7055	1,415	2,127	2,7
60	0,6842	1,371	2,062	2,616
70	0,6641	1,331	2	2,538
80	0,6451	1,292	1,942	2,464
90	0,6272	1,256	1,888	2,394
100	0,6103	1,222	1,836	2,328
110	0,5943	1,19	1,787	2,266
120	0,579	1,159	1,741	2,207
130	0,5646	1,13	1,697	2,15
140	0,5508	1,102	1,655	2,097

The density of gaseous chlorine at various temperatures and pressures is from 1.31 to 2.1 atm.

↓ t, °C | P, kPa →	133	160	186	213
-20	4,695	5,768	—	—
-10	4,446	5,389	6,366	7,389
0	4,255	5,138	6,036	6,954
10	4,092	4,933	5,783	6,645
20	3,945	4,751	5,565	6,385
30	3,809	4,585	5,367	6,154
40	3,682	4,431	5,184	5,942
50	3,563	4,287	5,014	5,745
60	3,452	4,151	4,855	5,561
70	3,347	4,025	4,705	5,388
80	3,248	3,905	4,564	5,225
90	3,156	3,793	4,432	5,073
100	3,068	3,687	4,307	4,929
110	2,985	3,587	4,189	4,793
120	2,907	3,492	4,078	4,665
130	2,832	3,397	3,972	4,543
140	2,761	3,319	3,87	4,426

Density of liquid chlorine

Liquid chlorine can exist in a relatively narrow temperature range, the boundaries of which lie from minus 100.5 to plus 144°C (that is, from the melting point to the critical temperature). Above a temperature of 144 ° C, chlorine will not go into a liquid state at any pressure. The density of liquid chlorine in this temperature range varies from 1717 to 573 kg/m 3 .

Density of liquid chlorine at various temperatures

t, °С	ρ, kg / m 3	t, °С	ρ, kg / m 3
-100	1717	30	1377
-90	1694	40	1344
-80	1673	50	1310
-70	1646	60	1275
-60	1622	70	1240
-50	1598	80	1199
-40	1574	90	1156
-30	1550	100	1109
-20	1524	110	1059
-10	1496	120	998
0	1468	130	920
10	1438	140	750
20	1408	144	573

Specific heat capacity of chlorine

The specific heat capacity of gaseous chlorine C p in kJ / (kg K) in the temperature range from 0 to 1200 ° C and normal atmospheric pressure can be calculated by the formula:

where T is the absolute temperature of chlorine in degrees Kelvin.

It should be noted that under normal conditions, the specific heat capacity of chlorine is 471 J/(kg K) and increases upon heating. The increase in heat capacity at temperatures above 500°C becomes insignificant, and at high temperatures the specific heat capacity of chlorine remains virtually unchanged.

The table shows the results of calculating the specific heat capacity of chlorine using the above formula (the calculation error is about 1%).

Specific heat capacity of chlorine gas as a function of temperature

t, °С	C p , J/(kg K)	t, °С	C p , J/(kg K)
0	471	250	506
10	474	300	508
20	477	350	510
30	480	400	511
40	482	450	512
50	485	500	513
60	487	550	514
70	488	600	514
80	490	650	515
90	492	700	515
100	493	750	515
110	494	800	516
120	496	850	516
130	497	900	516
140	498	950	516
150	499	1000	517
200	503	1100	517

At a temperature close to absolute zero, chlorine is in a solid state and has a low specific heat capacity (19 J/(kg·K)). As the temperature of solid Cl 2 increases, its heat capacity increases and reaches 720 J/(kg K) at minus 143°C.

Liquid chlorine has a specific heat capacity of 918 ... 949 J / (kg K) in the range from 0 to -90 degrees Celsius. According to the table, it can be seen that the specific heat of liquid chlorine is higher than that of gaseous chlorine and decreases with increasing temperature.

Thermal conductivity of chlorine

The table shows the values ​​of the thermal conductivity coefficients of gaseous chlorine at normal atmospheric pressure in the temperature range from -70 to 400°C.

The thermal conductivity coefficient of chlorine under normal conditions is 0.0079 W / (m deg), which is 3 times less than at the same temperature and pressure. Heating chlorine leads to an increase in its thermal conductivity. Thus, at a temperature of 100°C, the value of this physical property of chlorine increases to 0.0114 W/(m deg).

Thermal conductivity of chlorine gas

t, °С	λ, W/(m deg)	t, °С	λ, W/(m deg)
-70	0,0054	50	0,0096
-60	0,0058	60	0,01
-50	0,0062	70	0,0104
-40	0,0065	80	0,0107
-30	0,0068	90	0,0111
-20	0,0072	100	0,0114
-10	0,0076	150	0,0133
0	0,0079	200	0,0149
10	0,0082	250	0,0165
20	0,0086	300	0,018
30	0,009	350	0,0195
40	0,0093	400	0,0207

Viscosity of chlorine

The coefficient of dynamic viscosity of gaseous chlorine in the temperature range of 20 ... 500 ° C can be approximately calculated by the formula:

where η T is the coefficient of dynamic viscosity of chlorine at a given temperature T, K;
η T 0 is the coefficient of dynamic viscosity of chlorine at a temperature T 0 =273 K (at n.a.);
C is Sutherland's constant (for chlorine C=351).

Under normal conditions, the dynamic viscosity of chlorine is 0.0123·10 -3 Pa·s. When heated, such a physical property of chlorine as viscosity takes on higher values.

Liquid chlorine has an order of magnitude higher viscosity than gaseous chlorine. For example, at a temperature of 20°C, the dynamic viscosity of liquid chlorine has a value of 0.345·10 -3 Pa·s and decreases with increasing temperature.

Sources:

1. Barkov S. A. Halogens and a subgroup of manganese. Elements of group VII of the periodic system of D. I. Mendeleev. Student aid. M .: Education, 1976 - 112 p.
2. Tables of physical quantities. Directory. Ed. acad. I. K. Kikoina. Moscow: Atomizdat, 1976 - 1008 p.
3. Yakimenko L. M., Pasmanik M. I. Reference book on the production of chlorine, caustic soda and basic chlorine products. Ed. 2nd, trans. etc. M.: Chemistry, 1976 - 440 p.

Chlorine
atomic number	17
Appearance a simple substance	Yellow-green gas with a pungent odor. Poisonous.
Atom properties
Atomic mass (molar mass)	35.4527 amu (g/mol)
Atom radius	100 pm
Ionization energy (first electron)	1254.9(13.01) kJ/mol (eV)
Electronic configuration	3s 2 3p 5
Chemical properties
covalent radius	99 pm
Ion radius	(+7e)27 (-1e)181 pm
Electronegativity (according to Pauling)	3.16
Electrode potential	0
Oxidation states	7, 6, 5, 4, 3, 1, −1
Thermodynamic properties of a simple substance
Density	(at -33.6 °C)1.56 g/cm³
Molar heat capacity	21.838 J/(K mol)
Thermal conductivity	0.009 W /( K)
Melting temperature	172.2
Melting heat	6.41 kJ / mol
Boiling temperature	238.6
Heat of evaporation	20.41 kJ/mol
Molar volume	18.7 cm³/mol
The crystal lattice of a simple substance
Lattice structure	orthorhombic
Lattice parameters	a=6.29 b=4.50 c=8.21 Å
c/a ratio	—
Debye temperature	n/a K

Chlorine (χλωρός - green) - an element of the main subgroup of the seventh group, the third period of the periodic system of chemical elements, with atomic number 17.

The element Chlorine is represented by the symbol Cl(lat. Chlorum). Reactive nonmetal. It belongs to the group of halogens (originally, the name "halogen" was used by the German chemist Schweiger for chlorine [literally, "halogen" is translated as salt), but it did not take root, and subsequently became common for the VII group of elements, which includes chlorine).

simple substance chlorine(CAS number: 7782-50-5) Under normal conditions, a yellowish-green poisonous gas with a pungent odor. The chlorine molecule is diatomic (formula Cl 2).

The history of the discovery of chlorine

Chlorine atom diagram

Chlorine was first obtained in 1772 by Scheele, who described its release during the interaction of pyrolusite with hydrochloric acid in his treatise on pyrolusite:

4HCl + MnO 2 \u003d Cl 2 + MnCl 2 + 2H 2 O

Scheele noted the smell of chlorine, similar to the smell of aqua regia, its ability to interact with gold and cinnabar, as well as its bleaching properties.

Scheele, in accordance with the phlogiston theory prevailing in chemistry at that time, suggested that chlorine is a dephlogistic hydrochloric acid, i.e. hydrochloric acid oxide. Berthollet and Lavoisier suggested that chlorine is an oxide of the element muria, however, attempts to isolate it remained unsuccessful until the work of Davy, who managed to decompose table salt by electrolysis into sodium And chlorine.

Distribution in nature

In nature, there are two isotopes of chlorine 35 Cl and 37 Cl. Chlorine is the most abundant halogen in the earth's crust. Chlorine is very active - it combines directly with almost all elements of the periodic table.

In nature, it occurs only in the form of compounds in the composition of minerals: halite NaCI, sylvin KCl, sylvinite KCl NaCl, bischofite MgCl 2 6H2O, carnallite KCl MgCl 2 6H 2 O, kainite KCl MgSO 4 3H 2 O. Most large reserves of chlorine are contained in the salts of the waters of the seas and oceans.

Chlorine accounts for 0.025% of the total number of atoms in the earth's crust, the Clarke number of chlorine is 0.19%, and the human body contains 0.25% of chlorine ions by mass. In humans and animals, chlorine is found mainly in intercellular fluids (including blood) and plays an important role in the regulation of osmotic processes, as well as in processes associated with the functioning of nerve cells.

Isotopic composition

In nature, there are 2 stable isotopes of chlorine: with a mass number of 35 and 37. The proportions of their content are respectively 75.78% and 24.22%.

Isotope	Relative mass, a.m.u.	Half life	Decay type	nuclear spin
35Cl	34.968852721	stable	—	3/2
36Cl	35.9683069	301000 years	β-decay in 36 Ar	0
37Cl	36.96590262	stable	—	3/2
38Cl	37.9680106	37.2 minutes	β-decay in 38 Ar	2
39Cl	38.968009	55.6 minutes	β-decay in 39 Ar	3/2
40Cl	39.97042	1.38 minutes	β-decay in 40 Ar	2
41Cl	40.9707	34 c	β-decay in 41 Ar
42Cl	41.9732	46.8 s	β-decay in 42 Ar
43Cl	42.9742	3.3 s	β-decay in 43 Ar

Physical and physico-chemical properties

Under normal conditions, chlorine is a yellow-green gas with a suffocating odor. Some of its physical properties are presented in the table.

Property	Meaning
Boiling temperature	-34°C
Melting temperature	-101°C
Decomposition temperature (dissociations into atoms)	~1400°С
Density (gas, n.o.s.)	3.214 g/l
Affinity for the electron of an atom	3.65 eV
First ionization energy	12.97 eV
Heat capacity (298 K, gas)	34.94 (J/mol K)
Critical temperature	144°C
critical pressure	76 atm
Standard enthalpy of formation (298 K, gas)	0 (kJ/mol)
Standard entropy of formation (298 K, gas)	222.9 (J/mol K)
Enthalpy of fusion	6.406 (kJ/mol)
Boiling enthalpy	20.41 (kJ/mol)

When cooled, chlorine turns into a liquid at a temperature of about 239 K, and then below 113 K it crystallizes into an orthorhombic lattice with a space group cmca and parameters a=6.29 b=4.50 , c=8.21 . Below 100 K, the orthorhombic modification of crystalline chlorine transforms into the tetragonal one, which has a space group P4 2 /ncm and lattice parameters a=8.56 and c=6.12 .

Solubility

The degree of dissociation of the chlorine molecule Cl 2 → 2Cl. At 1000 K it is 2.07 * 10 -4%, and at 2500 K 0.909%.

The odor perception threshold in the air is 0.003 (mg/l).

In the CAS registry - number 7782-50-5.

In terms of electrical conductivity, liquid chlorine ranks among the strongest insulators: it conducts current almost a billion times worse than distilled water, and 10 22 times worse than silver. The speed of sound in chlorine is about one and a half times less than in air.

Chemical properties

The structure of the electron shell

The valence level of the chlorine atom contains 1 unpaired electron: 1S² 2S² 2p 6 3S² 3p 5, so the valency of 1 for the chlorine atom is very stable. Due to the presence of an unoccupied orbital of the d-sublevel in the chlorine atom, the chlorine atom can also exhibit other valences. Scheme of the formation of excited states of the atom:

Chlorine compounds are also known in which the chlorine atom formally exhibits valency 4 and 6, such as ClO 2 and Cl 2 O 6 . However, these compounds are radicals, meaning they have one unpaired electron.

Interaction with metals

Chlorine reacts directly with almost all metals (with some only in the presence of moisture or when heated):

Cl 2 + 2Na → 2NaCl 3Cl 2 + 2Sb → 2SbCl 3 3Cl 2 + 2Fe → 2FeCl 3

Interaction with non-metals

In the light or when heated, it actively reacts (sometimes with an explosion) with hydrogen by a radical mechanism. Mixtures of chlorine with hydrogen, containing from 5.8 to 88.3% hydrogen, explode when irradiated with the formation of hydrogen chloride. A mixture of chlorine and hydrogen in small concentrations burns with a colorless or yellow-green flame. The maximum temperature of the hydrogen-chlorine flame is 2200 °C.:

Cl 2 + H 2 → 2HCl 5Cl 2 + 2P → 2PCl 5 2S + Cl 2 → S 2 Cl 2 Cl 2 + 3F 2 (ex.) → 2ClF 3

Other properties

Cl 2 + CO → COCl 2

When dissolved in water or alkalis, chlorine dismutates, forming hypochlorous (and when heated perchloric) and hydrochloric acids, or their salts:

Cl 2 + H 2 O → HCl + HClO 3Cl 2 + 6NaOH → 5NaCl + NaClO 3 + 3H 2 O Cl 2 + Ca(OH) 2 → CaCl(OCl) + H 2 O 4NH 3 + 3Cl 2 → NCl 3 + 3NH 4Cl

Oxidizing properties of chlorine

Cl 2 + H 2 S → 2HCl + S

Reactions with organic substances

CH 3 -CH 3 + Cl 2 → C 2 H 6-x Cl x + HCl

Attaches to unsaturated compounds by multiple bonds:

CH 2 \u003d CH 2 + Cl 2 → Cl-CH 2 -CH 2 -Cl

Aromatic compounds replace a hydrogen atom with chlorine in the presence of catalysts (for example, AlCl 3 or FeCl 3):

C 6 H 6 + Cl 2 → C 6 H 5 Cl + HCl

How to get

Industrial Methods

Initially, the industrial method for producing chlorine was based on the Scheele method, that is, the reaction of pyrolusite with hydrochloric acid:

MnO 2 + 4HCl → MnCl 2 + Cl 2 + 2H 2 O

In 1867, Deacon developed a method for producing chlorine by catalytic oxidation of hydrogen chloride with atmospheric oxygen. The Deacon process is currently used to recover chlorine from hydrogen chloride, a by-product of industrial chlorination of organic compounds.

4HCl + O 2 → 2H 2 O + 2Cl 2

Today, chlorine is produced on an industrial scale together with sodium hydroxide and hydrogen by electrolysis of a sodium chloride solution:

2NaCl + 2H 2 O → H 2 + Cl 2 + 2NaOH Anode: 2Cl - - 2e - → Cl 2 0 Cathode: 2H 2 O + 2e - → H 2 + 2OH -

Since the electrolysis of water takes place in parallel with the electrolysis of sodium chloride, the total equation can be expressed as follows:

1.80 NaCl + 0.50 H 2 O → 1.00 Cl 2 + 1.10 NaOH + 0.03 H 2

Three variants of the electrochemical method for producing chlorine are used. Two of them are electrolysis with a solid cathode: diaphragm and membrane methods, the third is electrolysis with a liquid mercury cathode (mercury production method). In a number of electrochemical production methods, the easiest and most convenient method is electrolysis with a mercury cathode, but this method causes significant harm. environment as a result of evaporation and leakage of metallic mercury.

Diaphragm method with solid cathode

The cavity of the cell is divided by a porous asbestos partition - diaphragm - into the cathode and anode space, where the cathode and anode of the cell are respectively located. Therefore, such an electrolyzer is often called diaphragm electrolysis, and the production method is diaphragm electrolysis. A stream of saturated anolyte (NaCl solution) continuously enters the anode space of the diaphragm cell. As a result of the electrochemical process, chlorine is released at the anode due to the decomposition of halite, and hydrogen is released at the cathode due to the decomposition of water. In this case, the near-cathode zone is enriched with sodium hydroxide.

Membrane method with solid cathode

The membrane method is essentially similar to the diaphragm method, but the anode and cathode spaces are separated by a cation-exchange polymer membrane. The membrane production method is more efficient than the diaphragm method, but it is more difficult to use.

Mercury method with liquid cathode

The process is carried out in an electrolytic bath, which consists of an electrolyzer, a decomposer and a mercury pump, interconnected by communications. In the electrolytic bath, under the action of a mercury pump, mercury circulates, passing through the electrolyzer and the decomposer. The cathode of the cell is a stream of mercury. Anodes - graphite or low wear. Together with mercury, a stream of anolyte, a solution of sodium chloride, continuously flows through the electrolyzer. As a result of the electrochemical decomposition of chloride, chlorine molecules are formed at the anode, and the released sodium dissolves in mercury at the cathode, forming an amalgam.

Laboratory methods

In laboratories, to obtain chlorine, processes based on the oxidation of hydrogen chloride with strong oxidizing agents (for example, manganese (IV) oxide, potassium permanganate, potassium dichromate) are usually used:

2KMnO 4 + 16HCl → 2KCl + 2MnCl 2 + 5Cl 2 +8H 2 O K 2 Cr 2 O 7 + 14HCl → 3Cl 2 + 2KCl + 2CrCl 3 + 7H 2 O

Chlorine storage

Produced chlorine is stored in special "tanks" or pumped into steel cylinders high pressure. Cylinders with liquid chlorine under pressure have a special color - marsh color. It should be noted that during long-term use of chlorine cylinders, extremely explosive nitrogen trichloride accumulates in them, and therefore, from time to time, chlorine cylinders must be routinely flushed and cleaned from nitrogen chloride.

Chlorine quality standards

According to GOST 6718-93 “Liquid chlorine. Specifications» the following grades of chlorine are produced

Application

Chlorine is used in many industries, science and domestic needs:

The main ingredient in bleach is chlorine water.

• In the production of polyvinyl chloride, plastic compounds, synthetic rubber, which are used to make: insulation for wires, window profiles, packaging materials, clothing and footwear, linoleum and gramophone records, varnishes, equipment and foam plastics, toys, instrument parts, Construction Materials. Polyvinyl chloride is produced by polymerizing vinyl chloride, which today is most often obtained from ethylene in a chlorine-balanced method through an intermediate 1,2-dichloroethane.
• The bleaching properties of chlorine have been known since ancient times, although it is not chlorine itself that “bleaches”, but atomic oxygen, which is formed during the decomposition of hypochlorous acid: Cl 2 + H 2 O → HCl + HClO → 2HCl + O .. This method of bleaching fabrics, paper, Cardboard has been used for centuries.
• Production of organochlorine insecticides - substances that kill insects harmful to crops, but are safe for plants. A significant part of the produced chlorine is spent on obtaining plant protection products. One of the most important insecticides is hexachlorocyclohexane (often referred to as hexachlorane). This substance was first synthesized back in 1825 by Faraday, but found practical application only after more than 100 years - in the 30s of our century.
• It was used as a chemical warfare agent, as well as for the production of other chemical warfare agents: tap water, but they cannot offer an alternative to the disinfectant aftereffect of chlorine compounds. The materials from which water pipes are made interact with chlorinated water in different ways. tap water. Free chlorine in tap water significantly shortens the life of polyolefin-based pipelines: polyethylene pipes different kind, including cross-linked polyethylene, the larger known as PEX (PEX, PE-X). In the USA, to control the admission of pipelines made of polymeric materials for use in water supply systems with chlorinated water, 3 standards were forced to be adopted: ASTM F2023 in relation to pipes made of cross-linked polyethylene (PEX) and hot chlorinated water, ASTM F2263 in relation to polyethylene pipes all and chlorinated water and ASTM F2330 for multilayer (metal polymer) pipes and hot chlorinated water. A positive reaction in terms of durability when interacting with chlorinated water is demonstrated by copper combustion (intestines. Absorption and excretion of chlorine are closely related to sodium ions and bicarbonates, to a lesser extent with mineralocorticoids and the activity of Na + / K + - ATP-ase. 10- 15% of all chlorine, of this amount, from 1/3 to 1/2 - in erythrocytes... About 85% of chlorine is in the extracellular space.Chlorine is excreted from the body mainly with urine (90-95%), feces (4-8% ) and through the skin (up to 2%) Excretion of chlorine is associated with sodium and potassium ions, and reciprocally with HCO 3 - (acid-base balance).

  A person consumes 5-10 g of NaCl per day. The minimum human need for chlorine is about 800 mg per day. Baby gets required amount chlorine through mother's milk, which contains 11 mmol/l of chlorine. NaCl is necessary for the production of hydrochloric acid in the stomach, which promotes digestion and the destruction of pathogenic bacteria. At present, the role of chlorine in the occurrence of certain diseases in humans is not well understood, mainly due to the small number of studies. Suffice it to say that even recommendations on the daily intake of chlorine have not been developed. Human muscle tissue contains 0.20-0.52% chlorine, bone - 0.09%; in the blood - 2.89 g / l. In the body of an average person (body weight 70 kg) 95 g of chlorine. Every day with food, a person receives 3-6 g of chlorine, which in excess covers the need for this element.

  Chlorine ions are vital for plants. Chlorine is involved in energy metabolism in plants by activating oxidative phosphorylation. It is necessary for the formation of oxygen in the process of photosynthesis by isolated chloroplasts, stimulates auxiliary processes of photosynthesis, primarily those associated with the accumulation of energy. Chlorine has a positive effect on the absorption of oxygen, potassium, calcium, and magnesium compounds by the roots. An excessive concentration of chloride ions in plants can also have a negative side, for example, reduce the content of chlorophyll, reduce the activity of photosynthesis, and retard the growth and development of plants. But there are plants that, in the process of evolution, either adapted to soil salinity, or, in the struggle for space, occupied empty salt marshes where there is no competition. Plants growing in saline soils are called halophytes, they accumulate chloride during the growing season and then get rid of the excess through leaf fall or release chloride on the surface of leaves and branches and receive the double benefit of shading the surface from sunlight. In Russia, halophytes grow on salt domes, outcrops of salt deposits and saline depressions around the Baskunchak and Elton salt lakes.

  Among microorganisms, halophiles are also known - halobacteria - which live in highly saline waters or soils.

  Features of operation and precautions

  Chlorine is a toxic suffocating gas that, if it enters the lungs, causes burns to the lung tissue, suffocation. It has an irritant effect on the respiratory tract at a concentration in the air of about 0.006 mg / l (i.e. twice the chlorine odor threshold). Chlorine was one of the first chemical poisons used by Germany in the First world war. When working with chlorine, protective clothing, gas masks, and gloves should be used. On a short time to protect the respiratory organs from the ingress of chlorine, you can use a rag bandage moistened with a solution of sodium sulfite Na 2 SO 3 or sodium thiosulfate Na 2 S 2 O 3.

  MPC of chlorine in the atmospheric air is as follows: average daily - 0.03 mg/m³; maximum one-time - 0.1 mg / m³; in the working premises of an industrial enterprise - 1 mg / m³.

  Additional Information

  Chlorine production in Russia
  gold chloride
  Chlorine water
  Bleaching powder
  Reize's first base chloride
  Reize's second base chloride

  Chlorine compounds
  Hypochlorites
  Perchlorates
  Acid chlorides
  Chlorates
  chlorides
  Organochlorine compounds

  Analyzed

  — With the help of reference electrodes ESr-10101 analyzing the content of Cl- and K+.