Starting to consider the chemical and physical properties of hydrogen, it should be noted that in its usual state, this chemical element is in a gaseous form. The colorless hydrogen gas is odorless and tasteless. For the first time, this chemical element was called hydrogen after the scientist A. Lavoisier conducted experiments with water, according to the results of which, world science learned that water is a multicomponent liquid, which contains hydrogen. This event happened in 1787, but long before that date hydrogen was known to scientists as "combustible gas".
Hydrogen in nature
According to scientists, hydrogen is contained in the earth's crust and in water (approximately 11.2% of the total volume of water). This gas is part of many minerals that mankind has been extracting from the bowels of the earth for centuries. The properties of hydrogen are partially characteristic of oil, natural gases and clay, for organisms of animals and plants. But in its pure form, that is, not combined with other chemical elements of the periodic table, this gas is extremely rare in nature. This gas can be released to the surface of the earth during volcanic eruptions. Free hydrogen is present in trace amounts in the atmosphere.
Chemical properties of hydrogen
Since the chemical properties of hydrogen are not uniform, this chemical element belongs to both the I group of the Mendeleev system and the VII group of the system. Being a representative of the first group, hydrogen is, in fact, an alkali metal, which has an oxidation state of +1 in most of the compounds to which it belongs. The same valence is characteristic of sodium and other alkali metals. Due to these chemical properties, hydrogen is considered to be an element similar to these metals.
If we are talking about metal hydrides, then the hydrogen ion has a negative valence - its oxidation state is -1. Na + H- is built in the same way as for chloride Na + Cl-. This fact is the reason for attributing hydrogen to the VII group of the Mendeleev system. Hydrogen, being in the state of a molecule, provided that it stays in an ordinary environment, is inactive, and can combine exclusively with non-metals, which are more active for it. These metals include fluorine, in the presence of light, hydrogen combines with chlorine. If hydrogen is heated, then it becomes more active, entering into reactions with many elements of Mendeleev's periodic system.
Atomic hydrogen exhibits more active chemical properties than molecular hydrogen. Oxygen molecules form water - H2 + 1 / 2O2 = H2O. When hydrogen interacts with halogens, hydrogen halides H2 + Cl2 = 2HCl are formed, and hydrogen enters into this reaction in the absence of light and at sufficiently high negative temperatures - up to - 252 ° С. The chemical properties of hydrogen make it possible to use it for the reduction of many metals, since, when reacting, hydrogen absorbs oxygen from metal oxides, for example, CuO + H2 = Cu + H2O. Hydrogen participates in the formation of ammonia, interacting with nitrogen in the reaction 3H2 + N2 = 2NH3, but provided that a catalyst is used, and the temperature and pressure are increased.
A vigorous reaction occurs when hydrogen interacts with sulfur in the reaction H2 + S = H2S, the result of which is hydrogen sulfide. The interaction of hydrogen with tellurium and selenium is slightly less active. If there is no catalyst, then it reacts with pure carbon, hydrogen only on condition that high temperatures are created. 2H2 + C (amorphous) = CH4 (methane). In the process of hydrogen activity with some alkali and other metals, hydrides are obtained, for example, H2 + 2Li = 2LiH.
Physical properties of hydrogen
Hydrogen is a very light chemical. At least scientists say that at the moment, there is no lighter substance than hydrogen. Its mass is 14.4 times lighter than air, its density is 0.0899 g / l at 0 ° C. At temperatures of -259.1 ° C, hydrogen is capable of melting - this is a very critical temperature that is not typical for the transformation of most chemical compounds from one state to another. Only such an element as helium exceeds the physical properties of hydrogen in this regard. Liquefaction of hydrogen is difficult, since its critical temperature is (-240 ° C). Hydrogen is the most heat-generating gas known to mankind. All of the properties described above are the most significant physical properties of hydrogen that are used by humans for specific purposes. Also, these properties are the most relevant for modern science.
Hydrogen H is a chemical element, one of the most widespread in our Universe. The mass of hydrogen as an element in the composition of substances is 75% of the total content of atoms of another type. He enters into the most important and vital connection on the planet - water. A distinctive feature of hydrogen is also the fact that it is the first element in the periodic table of chemical elements of D. I. Mendeleev.
Discovery and exploration
The first mention of hydrogen in the writings of Paracelsus dates back to the sixteenth century. But its separation from the gas mixture of air and the study of the combustible properties were carried out already in the seventeenth century by the scientist Lemery. Hydrogen was thoroughly studied by an English chemist, physicist and naturalist who empirically proved that the mass of hydrogen is the smallest in comparison with other gases. In the subsequent stages of the development of science, many scientists worked with him, in particular Lavoisier, who called him "giving birth to water."
Characteristic by position in PSCE
The element that opens DI Mendeleev's periodic table is hydrogen. The physical and chemical properties of the atom show a certain duality, since hydrogen is simultaneously attributed to the first group, the main subgroup, if it behaves like a metal and gives up a single electron in the process of a chemical reaction, and to the seventh - in the case of complete filling of the valence shell, that is, negative particle, which characterizes it as similar to halogens.
Features of the electronic structure of the element
The properties of complex substances, which include it, and the simplest substance H 2, are primarily determined by the electronic configuration of the hydrogen. A particle has one electron with Z = (-1), which rotates in its orbit around a nucleus containing one proton with a unit mass and a positive charge (+1). Its electronic configuration is written as 1s 1, which means there is one negative particle on the very first and only s-orbital for hydrogen.
When an electron is detached or given up, and the atom of this element has such a property that it makes it related to metals, a cation is obtained. Essentially, a hydrogen ion is a positive elementary particle. Therefore, the hydrogen deprived of an electron is simply called a proton.
Physical properties
In short, hydrogen is a colorless, slightly soluble gas with a relative atomic mass of 2, 14.5 times lighter than air, with a liquefaction temperature of -252.8 degrees Celsius.
It can be easily seen from experience that H 2 is the lightest. To do this, it is enough to fill three balls with various substances - hydrogen, carbon dioxide, ordinary air - and simultaneously release them from your hand. The one filled with CO 2 will reach the ground the fastest, after which the inflated air mixture will go down, and the one containing H 2 will rise to the ceiling.
The small mass and size of hydrogen particles justify its ability to penetrate various substances. On the example of the same ball, this is easy to be convinced of, in a couple of days it will deflate itself, since the gas will simply pass through the rubber. Also, hydrogen can accumulate in the structure of some metals (palladium or platinum), and evaporate from it when the temperature rises.
The property of low solubility of hydrogen is used in laboratory practice to isolate it by displacing hydrogen (the table below contains the main parameters) determine the scope of its application and methods of production.
| Parameter of an atom or molecule of a simple substance | Meaning |
| Atomic mass (molar mass) | 1.008 g / mol |
| Electronic configuration | 1s 1 |
| Crystal cell | Hexagonal |
| Thermal conductivity | (300 K) 0.1815 W / (m K) |
| Density at n. at. | 0.08987 g / l |
| Boiling temperature | -252.76 ° C |
| Specific heat of combustion | 120.9 10 6 J / kg |
| Melting temperature | -259.2 ° C |
| Water solubility | 18.8 ml / l |
Isotopic composition
Like many other representatives of the periodic table of chemical elements, hydrogen has several natural isotopes, that is, atoms with the same number of protons in the nucleus, but a different number of neutrons - particles with zero charge and unit mass. Examples of atoms with a similar property are oxygen, carbon, chlorine, bromine and others, including radioactive ones.
The physical properties of hydrogen 1 H, the most common of the representatives of this group, differ significantly from the same characteristics of its counterparts. In particular, the characteristics of the substances in which they are included differ. So, there is ordinary and deuterated water, containing in its composition instead of a hydrogen atom with a single proton, deuterium 2 H - its isotope with two elementary particles: positive and uncharged. This isotope is twice as heavy as conventional hydrogen, which explains the dramatic difference in the properties of the compounds they make up. In nature, deuterium is found 3200 times less frequently than hydrogen. The third representative is tritium 3 H, in the nucleus it has two neutrons and one proton.
Methods for obtaining and isolating
Laboratory and industrial methods are quite different. So, in small quantities, gas is obtained mainly through reactions in which mineral substances are involved, and large-scale production uses organic synthesis to a greater extent.
The following chemical interactions are used in the laboratory:
In industrial interests, gas is obtained by such methods as:
- Thermal decomposition of methane in the presence of a catalyst to its constituent simple substances (350 degrees reaches the value of such an indicator as temperature) - hydrogen H 2 and carbon C.
- Passing vaporous water through coke at 1000 degrees Celsius to form carbon dioxide CO 2 and H 2 (the most common method).
- Conversion of gaseous methane on a nickel catalyst at temperatures reaching 800 degrees.
- Hydrogen is a by-product of the electrolysis of aqueous solutions of potassium or sodium chloride.
Chemical interactions: general provisions
The physical properties of hydrogen largely explain its behavior in reaction processes with this or that compound. The valency of hydrogen is 1, since it is located in the first group in the periodic table, and the oxidation state is different. In all compounds, except for hydrides, hydrogen in s.r. = (1+), in molecules of the type XH, XH 2, XH 3 - (1-).
The hydrogen gas molecule, formed by creating a generalized electron pair, consists of two atoms and is quite stable energetically, which is why it is somewhat inert under normal conditions and enters into a reaction when normal conditions change. Depending on the oxidation state of hydrogen in the composition of other substances, it can act as both an oxidizing agent and a reducing agent.
Substances with which it reacts and which forms hydrogen
Elemental interactions with the formation of complex substances (often at elevated temperatures):
- Alkaline and alkaline earth metal + hydrogen = hydride.
- Halogen + H 2 = hydrogen halide.
- Sulfur + hydrogen = hydrogen sulfide.
- Oxygen + H 2 = water.
- Carbon + hydrogen = methane.
- Nitrogen + H 2 = ammonia.
Interaction with complex substances:
- Production of synthesis gas from carbon monoxide and hydrogen.
- Reduction of metals from their oxides using Н 2.
- Hydrogen saturation of unsaturated aliphatic hydrocarbons.
Hydrogen bond
The physical properties of hydrogen are such that, being in conjunction with an electronegative element, it allows it to form a special type of bond with the same atom from neighboring molecules that have lone electron pairs (for example, oxygen, nitrogen and fluorine). The clearest example on which it is better to consider such a phenomenon is water. It can be said to be stitched with hydrogen bonds, which are weaker than covalent or ionic ones, but due to the fact that there are many of them, they have a significant effect on the properties of a substance. Essentially, hydrogen bonding is an electrostatic interaction that binds water molecules into dimers and polymers, justifying its high boiling point.
Hydrogen in mineral compounds
All contain a proton - a cation of an atom such as hydrogen. A substance whose acidic residue has an oxidation state greater than (-1) is called a polybasic compound. It contains several hydrogen atoms, which makes the dissociation in aqueous solutions multistage. Each subsequent proton is detached from the remainder of the acid more and more difficult. Its acidity is determined by the quantitative content of hydrogen in the medium.
Application in human activities
Cylinders with a substance, as well as containers with other liquefied gases, such as oxygen, have a specific appearance. They are painted a dark green with a bright red inscription "Hydrogen". Gas is pumped into a cylinder at a pressure of about 150 atmospheres. The physical properties of hydrogen, in particular the lightness of the gaseous state of aggregation, are used to fill balloons, balloons, etc., in a mixture with helium.
Hydrogen, the physical and chemical properties of which people learned to use many years ago, is currently used in many industries. Most of it goes to the production of ammonia. Hydrogen also participates in (hafnium, germanium, gallium, silicon, molybdenum, tungsten, zirconium and others) from oxides, acting in the reaction as a reducing agent, hydrocyanic and hydrochloric acids, as well as artificial liquid fuel. The food industry uses it to convert vegetable oils into solid fats.
Determined the chemical properties and use of hydrogen in various processes of hydrogenation and hydrogenation of fats, coal, hydrocarbons, oils and fuel oil. It is used to produce precious stones, incandescent lamps, forge and weld metal products under the influence of an oxygen-hydrogen flame.
Consider what hydrogen is. The chemical properties and production of this non-metal are studied in the course of inorganic chemistry at school. It is this element that heads the periodic system of Mendeleev, and therefore deserves a detailed description.
Opening an item at a glance
Before considering the physical and chemical properties of hydrogen, let's find out how this important element was found.
Chemists who worked in the sixteenth and seventeenth centuries repeatedly mentioned in their writings the combustible gas that is released when acids are exposed to active metals. In the second half of the eighteenth century, G. Cavendish managed to collect and analyze this gas, giving it the name "combustible gas".
The physical and chemical properties of hydrogen at that time were not studied. It was only at the end of the eighteenth century that A. Lavoisier succeeded by analysis to establish that this gas can be obtained by analyzing water. A little later, he began to call the new element hydrogene, which means “giving birth to water”. Hydrogen owes its modern Russian name to M.F.Soloviev.
Being in nature
The chemical properties of hydrogen can only be analyzed on the basis of its abundance in nature. This element is present in the hydro- and lithosphere, and is also a part of minerals: natural and associated gas, peat, oil, coal, oil shale. It is difficult to imagine an adult who would not know that hydrogen is an integral part of water.
In addition, this non-metal is found in animal organisms in the form of nucleic acids, proteins, carbohydrates, and fats. On our planet, this element is found in free form quite rarely, perhaps only in natural and volcanic gas.
In the form of plasma, hydrogen makes up about half the mass of stars and the Sun, and is also part of the interstellar gas. For example, in free form, as well as in the form of methane, ammonia, this non-metal is present in comets and even some planets.
Physical properties
Before considering the chemical properties of hydrogen, we note that under normal conditions it is a gaseous substance lighter than air and has several isotopic forms. It is almost insoluble in water and has a high thermal conductivity. Protium, which has a mass number of 1, is considered its lightest form. Tritium, which has radioactive properties, is naturally formed from atmospheric nitrogen when it is exposed to UV rays by neurons.
Features of the structure of the molecule
To consider the chemical properties of hydrogen, the reactions characteristic of it, let us dwell on the features of its structure. This diatomic molecule has a covalent non-polar chemical bond. The formation of atomic hydrogen is possible through the interaction of active metals with acid solutions. But in this form, this non-metal is able to exist only for a small time period, almost immediately it recombines into a molecular form.
Chemical properties
Consider the chemical properties of hydrogen. In most of the compounds that this chemical element forms, it exhibits an oxidation state of +1, which makes it similar to active (alkali) metals. The main chemical properties of hydrogen, which characterize it as a metal:
- interaction with oxygen to form water;
- reaction with halogens, accompanied by the formation of hydrogen halide;
- obtaining hydrogen sulfide when combined with sulfur.
Below is the equation of reactions characterizing the chemical properties of hydrogen. We draw attention to the fact that as a non-metal (with an oxidation state of -1) it acts only in a reaction with active metals, forming the corresponding hydrides with them.
At ordinary temperatures, hydrogen inactively interacts with other substances, so most of the reactions are carried out only after preliminary heating.
Let us dwell in more detail on some of the chemical interactions of the element that heads the periodic table of chemical elements of Mendeleev.
The reaction of water formation is accompanied by the release of 285.937 kJ of energy. At elevated temperatures (more than 550 degrees Celsius), this process is accompanied by a strong explosion.
Among those chemical properties of gaseous hydrogen that have found significant application in industry, its interaction with metal oxides is of interest. It is through catalytic hydrogenation in modern industry that metal oxides are processed, for example, pure metal is isolated from iron scale (mixed iron oxide). This method allows for efficient processing of scrap metal.
The synthesis of ammonia, which involves the interaction of hydrogen with nitrogen in the air, is also in demand in the modern chemical industry. Among the conditions for the occurrence of this chemical interaction, we note pressure and temperature.
Conclusion
It is hydrogen that is an inactive chemical under normal conditions. As the temperature rises, its activity increases significantly. This substance is in demand in organic synthesis. For example, by hydrogenation, ketones can be reduced to secondary alcohols, and aldehydes can be converted to primary alcohols. In addition, by hydrogenation, it is possible to convert unsaturated hydrocarbons of the ethylene and acetylene class into saturated compounds of the methane series. Hydrogen is rightfully considered a simple substance in demand in modern chemical production.
Hydrogen is a simple substance H 2 (dihydrogen, diprotium, light hydrogen).
Brief characteristic of hydrogen:
- Non-metal.
- A colorless gas that is difficult to liquefy.
- Poorly soluble in water.
- It dissolves better in organic solvents.
- Chemisorbed by metals: iron, nickel, platinum, palladium.
- Strong reducing agent.
- Interacts (at high temperatures) with non-metals, metals, metal oxides.
- Atomic hydrogen H 0, obtained by thermal decomposition of H 2, has the highest reducing ability.
- Isotopes of hydrogen:
- 1 H - protium
- 2 H - deuterium (D)
- 3 H - tritium (T)
- Relative molecular weight = 2.016
- Relative density of solid hydrogen (t = -260 ° C) = 0.08667
- Relative density of liquid hydrogen (t = -253 ° C) = 0.07108
- Overpressure (n.a.) = 0.08988 g / l
- melting point = -259.19 ° C
- boiling point = -252.87 ° C
- Volumetric coefficient of solubility of hydrogen:
- (t = 0 ° C) = 2.15;
- (t = 20 ° C) = 1.82;
- (t = 60 ° C) = 1.60;
1. Thermal decomposition of hydrogen(t = 2000-3500 ° C):
H 2 ↔ 2H 0
2. Interaction of hydrogen with non-metals:
- H 2 + F 2 = 2HF (t = -250 .. + 20 ° C)
- H 2 + Cl 2 = 2HCl (on combustion or in the light at room temperature):
- Cl 2 = 2Cl 0
- Cl 0 + H 2 = HCl + H 0
- H 0 + Cl 2 = HCl + Cl 0
- H 2 + Br 2 = 2HBr (t = 350-500 ° C, platinum catalyst)
- H 2 + I 2 = 2HI (t = 350-500 ° C, platinum catalyst)
- H 2 + O 2 = 2H 2 O:
- H 2 + O 2 = 2OH 0
- OH 0 + H 2 = H 2 O + H 0
- H 0 + O 2 = OH 0 + O 0
- O 0 + H 2 = OH 0 + H 0
- H 2 + S = H 2 S (t = 150..200 ° C)
- 3H 2 + N 2 = 2NH 3 (t = 500 ° C, iron catalyst)
- 2H 2 + C (coke) = CH 4 (t = 600 ° C, platinum catalyst)
- H 2 + 2C (coke) = C 2 H 2 (t = 1500..2000 ° C)
- H 2 + 2C (coke) + N 2 = 2HCN (t more than 1800 ° C)
3. Interaction of hydrogen with complex substances:
- 4H 2 + (Fe II Fe 2 III) O 4 = 3Fe + 4H 2 O (t more than 570 ° C)
- H 2 + Ag 2 SO 4 = 2Ag + H 2 SO 4 (t more than 200 ° C)
- 4H 2 + 2Na 2 SO 4 = Na 2 S + 4H 2 O (t = 550-600 ° C, catalyst Fe 2 O 3)
- 3H 2 + 2BCl 3 = 2B + 6HCl (t = 800-1200 ° C)
- H 2 + 2EuCl 3 = 2EuCl 2 + 2HCl (t = 270 ° C)
- 4H 2 + CO 2 = CH 4 + 2H 2 O (t = 200 ° C, catalyst CuO 2)
- H 2 + CaC 2 = Ca + C 2 H 2 (t more than 2200 ° C)
- H 2 + BaH 2 = Ba (H 2) 2 (t up to 0 ° C, solution)
4. Participation of hydrogen in redox reactions:
- 2H 0 (Zn, dil. HCl) + KNO 3 = KNO 2 + H 2 O
- 8H 0 (Al, conc. KOH) + KNO 3 = NH 3 + KOH + 2H 2 O
- 2H 0 (Zn, dil. HCl) + EuCl 3 = 2EuCl 2 + 2HCl
- 2H 0 (Al) + NaOH (conc.) + Ag 2 S = 2Ag ↓ + H 2 O + NaHS
- 2H 0 (Zn, dil. H 2 SO 4) + C 2 N 2 = 2HCN
Hydrogen compounds
D 2 - diduterium:
- Heavy hydrogen.
- A colorless gas that is difficult to liquefy.
- Dideuterium is contained in natural hydrogen 0.012-0.016% (by weight).
- In a gas mixture of dideuterium and protium, isotope exchange occurs at high temperatures.
- Poorly soluble in ordinary and heavy water.
- With ordinary water, isotopic exchange is negligible.
- Chemical properties are similar to light hydrogen, but dideuterium is less reactive.
- Relative molecular weight = 4.028
- Relative density of liquid dideuterium (t = -253 ° C) = 0.17
- melting point = -254.5 ° C
- boiling point = -249.49 ° C
T 2 - dithritium:
- Superheavy hydrogen.
- Colorless radioactive gas.
- The half-life is 12.34 years.
- In nature, dithritium is formed as a result of the bombardment of 14 N nuclei with cosmic radiation by neutrons; traces of dithritium are found in natural waters.
- Ditritium is obtained in a nuclear reactor by bombarding lithium with slow neutrons.
- Relative molecular weight = 6.032
- melting point = -252.52 ° C
- boiling point = -248.12 ° C
HD - deuterium hydrogen:
- Colorless gas.
- Does not dissolve in water.
- Chemical properties are similar to H 2.
- Relative molecular weight = 3.022
- Relative density of solid hydrogen deuteride (t = -257 ° C) = 0.146
- Overpressure (n.o.) = 0.135 g / l
- melting point = -256.5 ° C
- boiling point = -251.02 ° C
Hydrogen oxides
H 2 O - water:
- Colorless liquid.
- According to the isotopic composition of oxygen, water consists of H 2 16 O with admixtures of H 2 18 O and H 2 17 O
- According to the isotopic composition of hydrogen, water consists of 1 H 2 O with an admixture of HDO.
- Liquid water undergoes protolysis (H 3 O + and OH -):
- H 3 O + (oxonium cation) is the strongest acid in aqueous solution;
- OH - (hydroxide ion) is the strongest base in aqueous solution;
- Water is the weakest conjugate protolith.
- With many substances, water forms crystalline hydrates.
- Water is a chemically active substance.
- Water is a versatile liquid solvent for inorganic compounds.
- Relative molecular weight of water = 18.02
- Relative density of solid water (ice) (t = 0 ° C) = 0.917
- Relative density of liquid water:
- (t = 0 ° C) = 0.999841
- (t = 20 ° C) = 0.998203
- (t = 25 ° C) = 0.997044
- (t = 50 ° C) = 0.97180
- (t = 100 ° C) = 0.95835
- density (n.o.) = 0.8652 g / l
- melting point = 0 ° C
- boiling point = 100 ° C
- Ionic product of water (25 ° C) = 1.008 10 -14
1. Thermal decomposition of water:
2H 2 O ↔ 2H 2 + O 2 (above 1000 ° C)
D 2 O - deuterium oxide:
- Heavy water.
- Colorless hygroscopic liquid.
- The viscosity is higher than that of water.
- Mixes up with ordinary water in unlimited quantities.
- Semi-heavy water HDO is formed during isotope exchange.
- The dissolving power is lower than that of ordinary water.
- The chemical properties of deuterium oxide are similar to those of water, but all reactions are slower.
- Heavy water is present in natural water (mass ratio to ordinary water 1: 5500).
- Deuterium oxide is obtained by repeated electrolysis of natural water, in which heavy water accumulates in the remainder of the electrolyte.
- Relative molecular weight of heavy water = 20.03
- Relative density of liquid heavy water (t = 11.6 ° C) = 1.1071
- Relative density of liquid heavy water (t = 25 ° C) = 1.1042
- melting point = 3.813 ° C
- boiling point = 101.43 ° C
T 2 O - tritium oxide:
- Super heavy water.
- Colorless liquid.
- The viscosity is higher and the dissolving power is lower than that of ordinary and heavy water.
- Mixes up with regular and heavy water in unlimited quantities.
- Isotopic exchange with ordinary and heavy water leads to the formation of HTO, DTO.
- The chemical properties of superheavy water are similar to those of water, but all reactions proceed even more slowly than in heavy water.
- Traces of tritium oxide are found in natural water and the atmosphere.
- Superheavy water is obtained by passing tritium over red-hot copper oxide CuO.
- Superheavy Water Relative Molecular Weight = 22.03
- melting point = 4.5 ° C
Hydrogen H is the most abundant element in the Universe (about 75% by mass), on Earth - the ninth most abundant. The most important natural compound of hydrogen is water.
Hydrogen ranks first in the periodic table (Z = 1). It has the simplest atomic structure: the nucleus of an atom - 1 proton, surrounded by an electron cloud, consisting of 1 electron.
Under some conditions, hydrogen exhibits metallic properties (gives up an electron), in others - non-metallic (accepts an electron).
Hydrogen isotopes occur in nature: 1H - protium (the nucleus consists of one proton), 2H - deuterium (D - the nucleus consists of one proton and one neutron), 3H - tritium (T - the nucleus consists of one proton and two neutrons).
Simple substance hydrogen
A hydrogen molecule consists of two atoms linked by a covalent non-polar bond.
Physical properties. Hydrogen is a colorless, odorless, tasteless, non-toxic gas. The hydrogen molecule is not polar. Therefore, the forces of intermolecular interaction in gaseous hydrogen are small. This is manifested in low boiling points (-252.6 ° C) and melting (-259.2 ° C).
Hydrogen is lighter than air, D (by air) = 0.069; slightly soluble in water (100 volumes of H2O dissolves 2 volumes of H2). Therefore, hydrogen, when produced in a laboratory, can be collected by air or water displacement methods.
Hydrogen production
In the laboratory:
1.The action of dilute acids on metals:
Zn + 2HCl → ZnCl 2 + H 2
2. Interaction of alkali and u-z metals with water:
Ca + 2H 2 O → Ca (OH) 2 + H 2
3. Hydrolysis of hydrides: metal hydrides are readily decomposed by water to form the corresponding alkali and hydrogen:
NaH + H 2 O → NaOH + H 2
CaH 2 + 2H 2 O = Ca (OH) 2 + 2H 2
4. The action of alkalis on zinc or aluminum or silicon:
2Al + 2NaOH + 6H 2 O → 2Na + 3H 2
Zn + 2KOH + 2H 2 O → K 2 + H 2
Si + 2NaOH + H 2 O → Na 2 SiO 3 + 2H 2
5. Water electrolysis. To increase the electrical conductivity of water, an electrolyte is added to it, for example, NaOH, H 2 SO 4 or Na 2 SO 4. At the cathode, 2 volumes of hydrogen are formed, at the anode - 1 volume of oxygen.
2H 2 O → 2H 2 + O 2
Industrial production of hydrogen
1. Conversion of methane with steam, Ni 800 ° C (the cheapest):
CH 4 + H 2 O → CO + 3 H 2
CO + H 2 O → CO 2 + H 2
In total:
CH 4 + 2 H 2 O → 4 H 2 + CO 2
2. Water vapor through red-hot coke at 1000 о С:
C + H 2 O → CO + H 2
CO + H 2 O → CO 2 + H 2
The resulting carbon monoxide (IV) is absorbed by water, in this way 50% of industrial hydrogen is obtained.
3. Heating methane to 350 ° C in the presence of an iron or nickel catalyst:
CH 4 → C + 2H 2
4. By electrolysis of aqueous solutions of KCl or NaCl, as a by-product:
2Н 2 О + 2NaCl → Cl 2 + H 2 + 2NaOH
Chemical properties of hydrogen
- In compounds, hydrogen is always monovalent. It has an oxidation state of +1, but in metal hydrides it is -1.
- A hydrogen molecule consists of two atoms. The emergence of a bond between them is explained by the formation of a generalized pair of electrons H: H or H 2
- Due to this generalization of electrons, the H2 molecule is more energetically stable than its individual atoms. To break a molecule into atoms in 1 mole of hydrogen, it is necessary to expend 436 kJ energy: Н 2 = 2Н, ∆H ° = 436 kJ / mol
- This explains the relatively low activity of molecular hydrogen at ordinary temperatures.
- With many non-metals, hydrogen forms gaseous compounds such as RH 4, RH 3, RH 2, RH.
1) Forms hydrogen halides with halogens:
H 2 + Cl 2 → 2HCl.
At the same time, it explodes with fluorine, reacts with chlorine and bromine only when illuminated or heated, and with iodine only when heated.
2) With oxygen:
2H 2 + O 2 → 2H 2 O
with the release of heat. At ordinary temperatures, the reaction proceeds slowly, above 550 ° C - with an explosion. A mixture of 2 volumes of H 2 and 1 volume of O 2 is called an explosive gas.
3) When heated, it reacts vigorously with sulfur (much more difficult with selenium and tellurium):
H 2 + S → H 2 S (hydrogen sulfide),
4) With nitrogen with the formation of ammonia only on the catalyst and at elevated temperatures and pressures:
ЗН 2 + N 2 → 2NН 3
5) With carbon at high temperatures:
2H 2 + C → CH 4 (methane)
6) Forms hydrides with alkali and alkaline earth metals (hydrogen is an oxidizing agent):
Н 2 + 2Li → 2LiH
in metal hydrides, the hydrogen ion is negatively charged (oxidation state -1), that is, the hydride Na + H - is built like the chloride Na + Cl -
With complex substances:
7) With metal oxides (used for the reduction of metals):
CuO + H 2 → Cu + H 2 O
Fe 3 O 4 + 4H 2 → 3Fe + 4H 2 O
8) with carbon monoxide (II):
CO + 2H 2 → CH 3 OH
Synthesis - gas (a mixture of hydrogen and carbon monoxide) is of great practical importance, since, depending on temperature, pressure and catalyst, various organic compounds are formed, for example HCHO, CH 3 OH and others.
9) Unsaturated hydrocarbons react with hydrogen, turning into saturated ones:
C n H 2n + H 2 → C n H 2n + 2.
