For geochemistry, it is important to clarify the principle of distribution of chemical elements in the earth's crust. Why are some of them often found in nature, others much less common, and others even considered “museum rarities”?
A powerful tool for explaining many geochemical phenomena is the Periodic Law of D.I. Mendeleev. In particular, with its help the question of the prevalence of chemical elements in the earth’s crust can be investigated.
For the first time, the connection between the geochemical properties of elements and their position in the Periodic Table of Chemical Elements was shown by D.I. Mendeleev, V.I. Vernadsky and A.E. Fersman.
Rules (laws) of geochemistry
Mendeleev's rule
In 1869, while working on the periodic law, D.I. Mendeleev formulated the rule: “ Elements with low atomic weights are generally more abundant than elements with higher atomic weights"(see Appendix 1, Periodic Table of Chemical Elements). Later, with the discovery of the structure of the atom, it was shown that for chemical elements with low atomic mass the number of protons is approximately equal to the number of neutrons in the nuclei of their atoms, that is, the ratio of these two quantities is equal to or close to unity: for oxygen = 1.0; for aluminum
For less common elements, neutrons predominate in the nuclei of atoms and the ratio of their number to the number of protons is significantly greater than unity: for radium; for uranium = 1.59.
The “Mendeleev’s rule” was further developed in the works of the Danish physicist Niels Bohr and the Russian chemist, academician of the USSR Academy of Sciences Viktor Ivanovich Spitsyn.
 | Viktor Ivanovich Spitsyn (1902-1988) |
Oddo's Rule
In 1914, the Italian chemist Giuseppe Oddo formulated a different rule: “ The atomic weights of the most common elements are expressed in numbers that are multiples of four, or deviate slightly from such numbers" Later, this rule received some interpretation in the light of new data on the structure of atoms: a nuclear structure consisting of two protons and two neutrons is particularly strong.
Garkins' rule
In 1917, the American physical chemist William Draper Garkins (Harkins) drew attention to the fact that chemical elements with even atomic (ordinal) numbers are distributed in nature several times more than their neighboring elements with odd numbers. Calculations confirmed the observation: of the first 28 elements of the periodic table, 14 even ones make up 86%, and odd ones only 13.6% of the mass of the earth's crust.
In this case, the explanation may be the fact that chemical elements with odd atomic numbers contain particles that are not bound into helions and are therefore less stable.
There are many exceptions to the Harkins rule: for example, even noble gases are extremely poorly distributed, and odd aluminum Al is more widespread than even magnesium Mg. However, there are suggestions that this rule applies not so much to the earth’s crust as to the entire globe. Although there is no reliable data on the composition of the deep layers of the globe yet, some information suggests that the amount of magnesium in the entire globe is twice as much as aluminum. The amount of helium He in outer space is many times greater than its terrestrial reserves. This is perhaps the most common chemical element in the Universe.
Fersman's rule
A.E. Fersman clearly showed the dependence of the abundance of chemical elements in the earth’s crust on their atomic (ordinal) number. This dependence becomes especially obvious if you plot a graph in coordinates: atomic number - logarithm of the atomic clarke. The graph shows a clear trend: atomic clarks decrease with increasing atomic numbers of chemical elements.
Rice. . The prevalence of chemical elements in the earth's crust
Rice. 5. The abundance of chemical elements in the Universe
(log C – logarithms of atomic clarkes according to Fersman)
(data on the number of atoms are referred to 10 6 silicon atoms)
Solid curve – even Z values,
dotted – odd Z values
However, there are some deviations from this rule: some chemical elements significantly exceed the expected abundance values (oxygen O, silicon Si, calcium Ca, iron Fe, barium Ba), while others (lithium Li, beryllium Be, boron B) are much less common, than would be expected based on Fersman's rule. Such chemical elements are called respectively redundant And scarce.
The formulation of the basic law of geochemistry is given on p.
Answers on questions,
submitted for examination in the discipline “Physico-chemical processes in the environment” for third-year students of the specialty “Environmental management and audit in industry”
Abundance of atoms in the environment. Clarks of elements.
Clark element – a numerical estimate of the average content of an element in the earth’s crust, hydrosphere, atmosphere, the Earth as a whole, various types of rocks, space objects, etc. The Clarke of an element can be expressed in units of mass (%, g/t), or in atomic %. Introduced by Fersman, named after Frank Unglizort, an American geochemist.
Clark was the first to establish the quantitative abundance of chemical elements in the earth's crust. He also included the hydrosphere and atmosphere in the earth's crust. However, the mass of the hydrosphere is several percent, and the atmosphere is hundredths of a percent of the mass of the solid crust, so the Clark numbers mainly reflect the composition of the solid crust. Thus, in 1889 the clarkes were calculated for 10 elements, in 1924 - for 50 elements.
Modern radiometric, neutron activation, atomic adsorption and other methods of analysis make it possible to determine the content of chemical elements in rocks and minerals with great accuracy and sensitivity. Ideas about Clarks have changed. For example: Ge in 1898 Fox considered the clarke to be equal to n * 10 -10%. Ge was poorly studied and had no practical significance. In 1924, the Clarke for it was calculated as n*10 -9% (Clark and G. Washington). Later, Ge was discovered in coals, and its clarke increased to 0.p%. Ge is used in radio engineering, the search for germanium raw materials, a detailed study of the geochemistry of Ge showed that Ge is not so rare in the earth's crust, its clarke in the lithosphere is 1.4 * 10 -4%, almost the same as that of Sn, As, its much higher more in the earth's crust than Au, Pt, Ag.
The abundance of atoms in
Vernadsky introduced the concept of the dispersed state of chemical elements, and it was confirmed. All elements are present everywhere; we can only talk about the lack of sensitivity of the analysis, which does not allow us to determine the content of one or another element in the environment being studied. This proposition about the general dispersion of chemical elements is called the Clark-Vernadsky law.
Based on the clarks of the elements in the solid earth’s crust (about Vinogradov), almost ½ of the solid earth’s crust consists of O, i.e. The earth’s crust is an “oxygen sphere”, an oxygen substance.
Clarks of most elements do not exceed 0.01-0.0001% - these are rare elements. If these elements have a weak ability to concentrate, they are called sharply scattered (Br, In, Ra, I, Hf).
For example: For U and Br, the clarke values are ≈ 2.5*10 -4, 2.1* 10-4, respectively, but U is simply a rare element, because its deposits are known, and Br is rare, scattered, because it is not concentrated in the earth's crust. Microelements are elements contained in a given system in small quantities (≈ 0.01% or less). Thus, Al is a microelement in organisms and a macroelement in silicate rocks.
Classification of elements according to Vernadsky.
In the earth's crust, elements related according to the periodic table behave differently - they migrate into the earth's crust in different ways. Vernadsky took into account the most important moments in the history of elements in the earth's crust. The main importance was given to such phenomena and processes as radioactivity, reversibility and irreversibility of migration. Ability to provide minerals. Vernadsky identified 6 groups of elements:
noble gases (He, Ne, Ar, Kr, Xe) – 5 elements;
noble metals (Ru, Rh, Pd, Os, Ir, Pt, Au) – 7 elements;
cyclic elements (participating in complex cycles) – 44 elements;
scattered elements – 11 elements;
highly radioactive elements (Po, Ra, Rn, Ac, Th, Pa, U) – 7 elements;
rare earth elements – 15 elements.
Elements of group 3 by mass predominate in the earth's crust; they mainly consist of rocks, water, and organisms.
Ideas from everyday experience do not match real data. Thus, Zn, Cu are widely distributed in everyday life and technology, and Zr (zirconium) and Ti are rare elements for us. Although Zr in the earth's crust is 4 times more than Cu, and Ti is 95 times more. The “rarity” of these elements is explained by the difficulty of extracting them from ores.
Chemical elements interact with each other not in proportion to their masses, but in accordance with the number of atoms. Therefore, clarks can be calculated not only in mass%, but also in% of the number of atoms, i.e. taking into account atomic masses (Chirvinsky, Fersman). At the same time, the clarks of heavy elements decrease, and those of light elements increase.
For example:Calculation by the number of atoms gives a more contrasting picture of the prevalence of chemical elements - an even greater predominance of oxygen and the rarity of heavy elements.
When the average composition of the earth's crust was established, the question arose about the reason for the uneven distribution of elements. This flock is associated with the structural features of atoms.
Let us consider the connection between the values of clarkes and the chemical properties of elements.
Thus, the alkali metals Li, Na, K, Rb, Cs, Fr are chemically close to each other - one valence electron, but the clarke values are different - Na and K - ≈ 2.5; Rb - 1.5*10 -2; Li - 3.2*10 -3 ; Cs – 3.7 * 10 -4 ; Fr – artificial element. The clarke values differ sharply for F and Cl, Br and I, Si (29.5) and Ge (1.4*10 -4), Ba (6.5*10 -2) and Ra (2*10 -10) .
On the other hand, elements that are chemically different have similar clarke values – Mn (0.1) and P (0.093), Rb (1.5*10 -2) and Cl (1.7*10 -2).
Fersman plotted the dependence of the values of atomic clarks for even and odd elements of the Periodic Table on the atomic number of the element. It turned out that as the structure of the atomic nucleus becomes more complex (weighted), the clarke values of elements decrease. However, these dependencies (curves) turned out to be broken.
Fersman drew a hypothetical middle line, which gradually decreased as the ordinal number of the element increased. The scientist called the elements located above the middle line, forming peaks, excess (O, Si, Fe, etc.), and those located below the line - deficient (inert gases, etc.). From the obtained dependence it follows that the earth’s crust is dominated by light atoms, occupying the initial cells of the Periodic Table, the nuclei of which contain a small number of protons and neutrons. Indeed, after Fe (No. 26) there is not a single common element.
Further Oddo (Italian scientist) and Garkins (American scientist) in 1925-28. Another feature of the prevalence of elements was established. The Earth's crust is dominated by elements with even atomic numbers and atomic masses. Among neighboring elements, even-numbered elements almost always have higher clarks than odd-numbered elements. For the 9 most common elements (8 O, 14 Si, 13 Al, 26 Fe, 20 Ca, 11 Na, 19 K, 12 Mg, 22 Ti), the even mass clarkes total 86.43%, and the odd ones – 13.05 %. The clarkes of elements whose atomic mass is divisible by 4 are especially large, these are O, Mg, Si, Ca.
According to Fersman's research, nuclei of type 4q (q is an integer) make up 86.3% of the earth's crust. Less common are nuclei of type 4q+3 (12.7%) and very few nuclei of type 4q+1 and 4q+2 (1%).
Among the even elements, starting with He, every sixth has the highest clarkes: O (No. 8), Si (No. 14), Ca (No. 20), Fe (No. 26). For odd elements - a similar rule (starting with H) - N (No. 7), Al (No. 13), K (No. 19), Mg (No. 25).
So, nuclei with a small and even number of protons and neutrons predominate in the earth's crust.
Over time, the clarks have changed. So, as a result of radioactive decay, there was less U and Th, but more Pb. Processes such as gas dissipation and meteorite fallout also played a role in changing the clarke values of elements.
Main trends in chemical changes in the earth's crust. Large cycle of matter in the earth's crust.
CYCLE OF SUBSTANCES. The substance of the earth's crust is in continuous motion, caused by various reasons related to physical and chemical. properties of matter, planetary, geological, geographical and biological. conditions of the earth. This movement invariably and continuously occurs over geological time—at least one and a half and, apparently, no more than three billion years. In recent years, a new science of the geological cycle has grown - geochemistry, which has the task of studying chemistry. elements that build our planet. The main subject of her study are chemical movements. elements of the earth's substance, no matter what causes these movements. These movements of elements are called chemical migrations. elements. Among the migrations there are those during which the chemical the element inevitably returns to its original state after a longer or shorter period of time; history of such chemicals elements in the earth's crust can be reduced thus. to a reversible process and is presented in the form of a circular process, a cycle. This type of migration is not typical for all elements, but for a significant number of them, including the vast majority of chemical elements. elements that build plant or animal organisms and the environment around us - oceans and waters, rocks and air. For such elements, the entire or overwhelming mass of their atoms is in the cycle of substances; for others, only an insignificant part of them is covered by the cycles. There is no doubt that most of the material of the earth's crust to a depth of 20-25 km is covered by gyres. For the following chem. elements, circular processes are characteristic and dominant among their migrations (the number indicates the ordinal number). H, Be4, B5, C«, N7, 08, P9, Nan, Mg12, Aha, Sii4, Pi5, Sie, Cli7, K19, Ca2o, Ti22, V23, Cr24, Mn25, Fe2e, Co27, Ni28, Cu29, Zn30 , Ge32, As33,Se34, Sr38,Mo42, Ag47,Cd48, Sn50, Sb51, Te62, Ba56) W74, Au79,Hg80,T]81,Pb82,Bi83. These elements can on this basis be separated from other elements as cyclic or organogenic elements. That. cycles characterize 42 elements out of 92 elements included in the Mendeleev system, and this number includes the most common dominant earthly elements.
Let us dwell on the first kind of cyclones, which involve biogenic migrations. These K. capture the biosphere (that is, the atmosphere, hydrosphere, weathering crust). Under the hydrosphere, they capture the basalt shell approaching the ocean floor. Under the land, they, in a sequence of depressions, embrace the thickness of sedimentary rocks (stratosphere), metamorphic and granite shells and enter the basalt shell. From the depths of the earth, lying behind the basalt shell, the substance of the earth does not fall into the observed K. It also does not fall into them from above because of the upper parts of the stratosphere. That. chemical cycles elements are surface phenomena occurring in the atmosphere to altitudes of 15-20 km (no higher), and in the lithosphere no deeper than 15-20 km. Every K., in order for it to be constantly renewed, requires an influx of external energy. Two main ones are known and there is no doubt. source of such energy: 1) cosmic energy - radiation from the sun (biogenic migration almost entirely depends on it) and 2) atomic energy associated with the radioactive decay of elements of the 78 series of uranium, thorium, potassium, rubidium. With a lesser degree of accuracy, mechanical energy can be distinguished , associated with the movement (due to gravity) of the earth's masses, and probably cosmic energy penetrating from above (Hess's rays).
The gyres, which involve several layers of the earth, proceed slowly, with stops, and can only be seen in geological time. They often span several geological periods. They are caused by geologist, displacements of land and ocean. Parts of K. can move quickly (for example, biogenic migration).
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Hydrogen (H) is a very light chemical element, with a content of 0.9% by weight in the Earth's crust and 11.19% in water.
Characteristics of hydrogen
It is the first among gases in lightness. Under normal conditions, it is tasteless, colorless, and absolutely odorless. When it enters the thermosphere, it flies off into space due to its low weight.
In the entire universe, it is the most numerous chemical element (75% of the total mass of substances). So much so that many stars in outer space are made entirely of it. For example, the Sun. Its main component is hydrogen. And heat and light are the result of the release of energy when the nuclei of a material merge. Also in space there are entire clouds of its molecules of various sizes, densities and temperatures.
Physical properties
High temperature and pressure significantly change its qualities, but under normal conditions it:
It has high thermal conductivity when compared with other gases,
Non-toxic and poorly soluble in water,
With a density of 0.0899 g/l at 0°C and 1 atm.,
Turns into liquid at a temperature of -252.8°C
Becomes hard at -259.1°C.,
Specific heat of combustion 120.9.106 J/kg.
It requires high pressure and very low temperatures to turn into a liquid or solid. In a liquefied state, it is fluid and light.
Chemical properties
Under pressure and upon cooling (-252.87 degrees C), hydrogen acquires a liquid state, which is lighter in weight than any analogue. It takes up less space in it than in gaseous form.
It is a typical non-metal. In laboratories, it is produced by reacting metals (such as zinc or iron) with dilute acids. Under normal conditions it is inactive and reacts only with active non-metals. Hydrogen can separate oxygen from oxides, and reduce metals from compounds. It and its mixtures form hydrogen bonds with certain elements.
The gas is highly soluble in ethanol and in many metals, especially palladium. Silver does not dissolve it. Hydrogen can be oxidized during combustion in oxygen or air, and when interacting with halogens.
When it combines with oxygen, water is formed. If the temperature is normal, then the reaction proceeds slowly; if it is above 550°C, it explodes (it turns into detonating gas).
Finding hydrogen in nature
Although there is a lot of hydrogen on our planet, it is not easy to find in its pure form. A little can be found during volcanic eruptions, during oil production and where organic matter decomposes.
More than half of the total amount is in the composition with water. It is also included in the structure of oil, various clays, flammable gases, animals and plants (presence in every living cell is 50% by the number of atoms).
Hydrogen cycle in nature
Every year, a colossal amount (billions of tons) of plant residues decomposes in water bodies and soil, and this decomposition releases a huge mass of hydrogen into the atmosphere. It is also released during any fermentation caused by bacteria, combustion and, along with oxygen, participates in the water cycle.
Hydrogen Applications
The element is actively used by humanity in its activities, so we have learned to obtain it on an industrial scale for:
Meteorology, chemical production;
Margarine production;
As rocket fuel (liquid hydrogen);
Electric power industry for cooling electric generators;
Welding and cutting of metals.
A lot of hydrogen is used in the production of synthetic gasoline (to improve the quality of low-quality fuel), ammonia, hydrogen chloride, alcohols, and other materials. Nuclear energy actively uses its isotopes.
The drug “hydrogen peroxide” is widely used in metallurgy, the electronics industry, pulp and paper production, for bleaching linen and cotton fabrics, for the production of hair dyes and cosmetics, polymers and in medicine for the treatment of wounds.
The "explosive" nature of this gas can become a lethal weapon - a hydrogen bomb. Its explosion is accompanied by the release of a huge amount of radioactive substances and is destructive for all living things.
Contact of liquid hydrogen and skin can cause severe and painful frostbite.
The chemical composition of the earth's crust was determined based on the results of the analysis of numerous samples of rocks and minerals that came to the surface of the earth during mountain-forming processes, as well as taken from mine workings and deep boreholes.
Currently, the earth's crust has been studied to a depth of 15-20 km. It consists of chemical elements that are part of rocks.
The most common elements in the earth's crust are 46, of which 8 make up 97.2-98.8% of its mass, 2 (oxygen and silicon) - 75% of the Earth's mass.
The first 13 elements (with the exception of titanium), most often found in the earth's crust, are part of the organic matter of plants, participate in all vital processes and play an important role in soil fertility. A large number of elements participating in chemical reactions in the bowels of the Earth lead to the formation of a wide variety of compounds. The chemical elements that are most abundant in the lithosphere are found in many minerals (mostly different rocks are made up of them).
Individual chemical elements are distributed in geospheres as follows: oxygen and hydrogen fill the hydrosphere; oxygen, hydrogen and carbon form the basis of the biosphere; oxygen, hydrogen, silicon and aluminum are the main components of clays and sands or weathering products (they mainly make up the upper part of the Earth's crust).
Chemical elements in nature are found in a variety of compounds called minerals. These are homogeneous chemical substances of the earth's crust that were formed as a result of complex physicochemical or biochemical processes, for example rock salt (NaCl), gypsum (CaS04*2H20), orthoclase (K2Al2Si6016).
In nature, chemical elements take an unequal part in the formation of different minerals. For example, silicon (Si) is a component of more than 600 minerals and is also very common in the form of oxides. Sulfur forms up to 600 compounds, calcium - 300, magnesium -200, manganese - 150, boron - 80, potassium - up to 75, only 10 lithium compounds are known, and even fewer iodine compounds.
Among the best known minerals in the earth's crust, a large group of feldspars with three main elements predominates - K, Na and Ca. In soil-forming rocks and their weathering products, feldspars occupy a major position. Feldspars gradually weather (disintegrate) and enrich the soil with K, Na, Ca, Mg, Fe and other ash substances, as well as microelements.
Clark number- numbers expressing the average content of chemical elements in the earth’s crust, hydrosphere, Earth, cosmic bodies, geochemical or cosmochemical systems, etc., in relation to the total mass of this system. Expressed in % or g/kg.
Types of clarks
There are weight (%, g/t or g/g) and atomic (% of the number of atoms) clarks. A generalization of data on the chemical composition of various rocks that make up the earth's crust, taking into account their distribution to depths of 16 km, was first made by the American scientist F. W. Clark (1889). The numbers he obtained for the percentage of chemical elements in the composition of the earth's crust, subsequently somewhat refined by A.E. Fersman, at the latter's suggestion, were called Clark numbers or Clarks.
Molecule structure. Electrical, optical, magnetic and other properties of molecules are related to the wave functions and energies of various states of the molecules. Molecular spectra provide information about the states of molecules and the probability of transition between them.
The vibration frequencies in the spectra are determined by the masses of atoms, their location and the dynamics of interatomic interactions. The frequencies in the spectra depend on the moments of inertia of the molecules, the determination of which from spectroscopic data allows one to obtain accurate values of interatomic distances in the molecule. The total number of lines and bands in the vibrational spectrum of a molecule depends on its symmetry.
Electronic transitions in molecules characterize the structure of their electronic shells and the state of chemical bonds. The spectra of molecules that have a greater number of bonds are characterized by long-wave absorption bands falling in the visible region. Substances that are built from such molecules are characterized by color; These substances include all organic dyes.
Ions. As a result of electron transitions, ions are formed - atoms or groups of atoms in which the number of electrons is not equal to the number of protons. If an ion contains more negatively charged particles than positively charged ones, then such an ion is called negative. Otherwise, the ion is called positive. Ions are very common in substances; for example, they are found in all metals without exception. The reason is that one or more electrons from each metal atom are separated and move within the metal, forming what is called an electron gas. It is due to the loss of electrons, that is, negative particles, that metal atoms become positive ions. This is true for metals in any state - solid, liquid or gas.
The crystal lattice models the arrangement of positive ions inside a crystal of a homogeneous metallic substance.
It is known that in the solid state all metals are crystals. The ions of all metals are arranged in an orderly manner, forming a crystal lattice. In molten and evaporated (gaseous) metals, there is no ordered arrangement of ions, but electron gas still remains between the ions.
Isotopes- varieties of atoms (and nuclei) of a chemical element that have the same atomic (ordinal) number, but at the same time different mass numbers. The name is due to the fact that all isotopes of one atom are placed in the same place (in one cell) of the periodic table. The chemical properties of an atom depend on the structure of the electron shell, which, in turn, is determined mainly by the charge of the nucleus Z (that is, the number of protons in it), and almost do not depend on its mass number A (that is, the total number of protons Z and neutrons N) . All isotopes of the same element have the same nuclear charge, differing only in the number of neutrons. Typically, an isotope is designated by the symbol of the chemical element to which it belongs, with the addition of an upper left suffix indicating the mass number. You can also write the name of the element followed by a hyphenated mass number. Some isotopes have traditional proper names (for example, deuterium, actinon).