Let us consider the chemical properties of alkaline earth metals. Let us determine the features of their structure, production, occurrence in nature, and application.
Position in the PS
First, let's determine the location of these elements in Mendeleev. They are located in the second group of the main subgroup. These include calcium, strontium, radium, barium, magnesium, and beryllium. All of them do not contain two valence electrons. In general, beryllium, magnesium and alkaline earth metals have ns2 electrons in their outer shell. In chemical compounds they exhibit an oxidation state of +2. When interacting with other substances, they exhibit reducing properties, donating electrons from the external energy level.
Changing Properties
As the nucleus of an atom grows, beryllium and magnesium increase their metallic properties, as the radius of their atoms increases. Let's consider the physical properties of alkaline earth metals. Beryllium in its normal state is a gray metal with a steely luster. It has a dense hexagonal crystal lattice. Upon contact with atmospheric oxygen, beryllium immediately forms an oxide film, as a result of which its chemical activity decreases and a matte coating is formed.
Physical properties
Magnesium as a simple substance is a white metal that forms an oxide coating in air. It has a hexagonal crystal lattice.
The physical properties of the alkaline earth metals calcium, barium, and strontium are similar. They are metals with a characteristic silvery luster, which become covered with a yellowish film under the influence of atmospheric oxygen. Calcium and strontium have a face-centered cubic lattice, while barium has a body-centered structure.
The chemistry of alkaline earth metals is based on the fact that they have a metallic bond. That is why they are characterized by high electrical and thermal conductivity. Their melting and boiling points are higher than those of alkali metals.
Methods of obtaining
Beryllium is produced on an industrial scale by recovering the metal from fluoride. The condition for this chemical reaction to occur is preheating.
Considering that alkaline earth metals occur in nature in the form of compounds, to obtain magnesium, strontium, and calcium, electrolysis of molten salts is carried out.
Chemical properties
The chemical properties of alkaline earth metals are associated with the need to first remove the oxide film layer from their surface. It is this that determines the inertness of these metals to water. Calcium, barium, and strontium, when dissolved in water, form hydroxides that have pronounced basic properties.
The chemical properties of alkaline earth metals suggest their interaction with oxygen. For barium, the reaction product is peroxide; for all others, oxides are formed after the reaction. All representatives of this class of oxides exhibit basic properties; only beryllium oxide is characterized by amphoteric properties.
The chemical properties of alkaline earth metals also manifest themselves in reactions with sulfur, halogens, and nitrogen. When reacting with acids, dissolution of these elements is observed. Considering that beryllium is an amphoteric element, it is capable of chemical interaction with alkali solutions.
Qualitative reactions
The basic formulas of alkaline earth metals discussed in the course of inorganic chemistry are associated with salts. To identify representatives of this class in a mixture with other elements, a qualitative definition can be used. When salts of alkaline earth metals are added to the flame of an alcohol lamp, coloring of the flame by cations is observed. The strontium cation produces a dark red tint, the calcium cation produces an orange tint, and the barium cation produces a green tint.
To identify the barium cation in qualitative analysis, sulfate anions are used. As a result of this reaction, white barium sulfate is formed, which is insoluble in inorganic acids.
Radium is a radioactive element that occurs in nature in trace amounts. When magnesium interacts with oxygen, a blinding flash is observed. This process has been used for some time when photographing in dark rooms. Magnesium flares have now been replaced by electrical systems. Beryllium is a member of the alkaline earth metal family, which reacts with many chemicals. Calcium and magnesium, like aluminum, can reduce such rare metals as titanium, tungsten, molybdenum, niobium. The data are called calcithermia and magnesothermia.
Features of application
What are the uses of alkaline earth metals? Calcium and magnesium are used to make light alloys and rare metals.
For example, magnesium is contained in duralumin, and calcium is a component of lead alloys used to produce cable sheaths and create bearings. Alkaline earth metals are widely used in technology in the form of oxides. (calcium oxide) and burnt magnesium (magnesium oxide) are required for the construction industry.
When calcium oxide interacts with water, a significant amount of heat is released. (calcium hydroxide) is used for construction. The white suspension of this substance (lime milk) is used in the sugar industry for the process of purifying beet juice.
Salts of metals of the second group
Salts of magnesium, beryllium, and alkaline earth metals can be obtained by reacting with acids of their oxides. Chlorides, fluorides, and iodides of these elements are white crystalline substances, generally highly soluble in water. Among sulfates, only magnesium and beryllium compounds are soluble. Its decrease is observed from beryllium salts to barium sulfates. Carbonates are practically insoluble in water or have minimal solubility.
Sulfides of alkaline earth elements are found in small quantities in heavy metals. If you shine light on them, you can get different colors. Sulfides are included in luminous compounds called phosphors. Similar paints are used to create luminous dials and road signs.
Common alkaline earth metal compounds
Calcium carbonate is the most common element on the earth's surface. It is an integral part of compounds such as limestone, marble, chalk. Among them, limestone has the main use. This mineral is indispensable in construction and is considered an excellent building stone. In addition, quicklime and slaked lime, glass, and cement are obtained from this inorganic compound.
The use of limestone helps strengthen roads, and thanks to the powder, soil acidity can be reduced. represents the shells of ancient animals. This compound is used to make rubber, paper, and school crayons.
Marble is in demand among architects and sculptors. Many of Michelangelo's unique creations were created from marble. Some Moscow metro stations are lined with marble tiles. Magnesium carbonate is used in large quantities in the manufacture of brick, cement, and glass. It is needed in the metallurgical industry to remove waste rock.
Calcium sulfate, found naturally in the form of gypsum (calcium sulfate crystalline hydrate), is used in the construction industry. In medicine, this compound is used to make impressions, as well as to create plaster casts.
Alabaster (semi-hydrous gypsum) releases a huge amount of heat when interacting with water. This is also applied in industry.
Epsom salts (magnesium sulfate) are used medicinally as a laxative. This substance has a bitter taste and is found in sea water.
“Barite porridge” (barium sulfate) does not dissolve in water. That is why this salt is used in x-ray diagnostics. Salt blocks X-rays, which makes it possible to detect diseases of the gastrointestinal tract.
Phosphorites (rock) and apatites contain calcium phosphate. They are needed to obtain calcium compounds: oxides, hydroxides.
Calcium plays a special role in living organisms. It is this metal that is necessary to build the bone skeleton. Calcium ions are necessary to regulate heart function and increase blood clotting. Its deficiency causes disturbances in the functioning of the nervous system, loss of coagulability, and loss of the ability of the hands to hold various objects normally.
In order to avoid health problems, a person should consume approximately 1.5 grams of calcium every day. The main problem is that in order for the body to absorb 0.06 grams of calcium, you need to eat 1 gram of fat. The maximum amount of this metal is found in lettuce, parsley, cottage cheese, and cheese.
Conclusion
All representatives of the second group of the main subgroup of the periodic table are necessary for the life and activity of modern man. For example, magnesium is a stimulator of metabolic processes in the body. It must be present in nervous tissue, blood, bones, and liver. Magnesium is an active participant in photosynthesis in plants, as it is a component of chlorophyll. Human bones make up about a fifth of the total weight. They contain calcium and magnesium. Oxides and salts of alkaline earth metals have found various applications in the construction industry, pharmaceuticals and medicine.
alkaline earth metals and, alkaline earth metals chemistryAlkaline earth metals- chemical elements of the 2nd group of the periodic table of elements: calcium, strontium, barium and radium.
- 1 Physical properties
- 2 Chemical properties
- 2.1 Simple substances
- 2.2 Oxides
- 2.3 Hydroxides
- 3 Being in nature
- 4 Biological role
- 5 Notes
Physical properties
Alkaline earth metals include only calcium, strontium, barium and radium, and less commonly magnesium. The first element of this subgroup, beryllium, in most properties is much closer to aluminum than to the higher analogues of the group to which it belongs. The second element in this group, magnesium, differs in some respects significantly from the alkaline earth metals in a number of chemical properties. All alkaline earth metals are gray substances that are solid at room temperature. Unlike alkali metals, they are significantly harder and generally cannot be cut with a knife (the exception is strontium. An increase in the density of alkaline earth metals is observed only starting with calcium. The heaviest is radium, comparable in density to germanium (ρ = 5.5 g/cm3) .
| Atomic number |
Name, symbol |
Number of natural isotopes | Atomic mass | Ionization energy, kJ mol−1 | Electron affinity, kJ mol−1 | EO | Metal. radius, nm | Ionic radius, nm | tpl, °C |
tboiling, °C |
ρ, g/cm³ |
ΔHpl, kJ mol−1 | ΔHboiling, kJ mol−1 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 4 | Beryllium Be | 1+11a | 9,012182 | 898,8 | 0,19 | 1,57 | 0,169 | 0,034 | 1278 | 2970 | 1,848 | 12,21 | 309 |
| 12 | Magnesium Mg | 3+19a | 24,305 | 737,3 | 0,32 | 1,31 | 0,24513 | 0,066 | 650 | 1105 | 1,737 | 9,2 | 131,8 |
| 20 | Calcium Ca | 5+19a | 40,078 | 589,4 | 0,40 | 1,00 | 0,279 | 0,099 | 839 | 1484 | 1,55 | 9,20 | 153,6 |
| 38 | Strontium Sr | 4+35a | 87,62 | 549,0 | 1,51 | 0,95 | 0,304 | 0,112 | 769 | 1384 | 2,54 | 9,2 | 144 |
| 56 | Barium Ba | 7+43a | 137,327 | 502,5 | 13,95 | 0,89 | 0,251 | 0,134 | 729 | 1637 | 3,5 | 7,66 | 142 |
| 88 | Radium Ra | 46a | 226,0254 | 509,3 | - | 0,9 | 0,2574 | 0,143 | 700 | 1737 | 5,5 | 8,5 | 113 |
a Radioactive isotopes
Chemical properties
Alkaline earth metals have the electronic configuration of the outer energy level ns², and are s-elements, along with the alkali metals. Having two valence electrons, alkaline earth metals easily give them up, and in all compounds they have an oxidation state of +2 (very rarely +1).
The chemical activity of alkaline earth metals increases with increasing atomic number. Beryllium in its compact form does not react with oxygen or halogens even at red heat temperatures (up to 600 °C; reaction with oxygen and other chalcogens requires an even higher temperature, fluorine is an exception). Magnesium is protected by an oxide film at room temperature and higher temperatures (up to 650 °C) and does not oxidize further. Calcium oxidizes slowly and deeply at room temperature (in the presence of water vapor), and burns with slight heating in oxygen, but is stable in dry air at room temperature. Strontium, barium and radium quickly oxidize in air, giving a mixture of oxides and nitrides, so they, like alkali metals and calcium, are stored under a layer of kerosene.
Also, unlike alkali metals, alkaline earth metals do not form superoxides and ozonides.
Oxides and hydroxides of alkaline earth metals tend to increase their basic properties with increasing atomic number.
Simple substances
Beryllium reacts with weak and strong acid solutions to form salts:
however, it is passivated by cold concentrated nitric acid.
The reaction of beryllium with aqueous solutions of alkalis is accompanied by the release of hydrogen and the formation of hydroxoberyllates:
When carrying out a reaction with an alkali melt at 400-500 °C, dioxoberyllates are formed:
Magnesium, calcium, strontium, barium and radium react with water to form alkalis (except for magnesium, which reacts with water only when hot magnesium powder is added to water):
Also, calcium, strontium, barium and radium react with hydrogen, nitrogen, boron, carbon and other non-metals to form the corresponding binary compounds:
Oxides
Beryllium oxide is an amphoteric oxide, dissolves in concentrated mineral acids and alkalis to form salts:
but with less strong acids and bases the reaction no longer occurs.
Magnesium oxide does not react with dilute and concentrated bases, but reacts easily with acids and water:
Oxides of calcium, strontium, barium and radium are basic oxides that react with water, strong and weak acid solutions and amphoteric oxides and hydroxides:
Hydroxides
Beryllium hydroxide is amphoteric, in reactions with strong bases it forms beryllates, and with acids - beryllium salts of acids:
Magnesium, calcium, strontium, barium and radium hydroxides are bases, the strength increases from weak to very strong, being the strongest corrosive substance, exceeding potassium hydroxide in activity. They are highly soluble in water (except for magnesium and calcium hydroxides). They are characterized by reactions with acids and acid oxides and with amphoteric oxides and hydroxides:
Being in nature
All alkaline earth metals are found (in varying quantities) in nature. Due to their high chemical activity, all of them are not found in a free state. The most common alkaline earth metal is calcium, the amount of which is 3.38% (by weight of the earth’s crust). It is slightly inferior to magnesium, the amount of which is 2.35% (of the mass of the earth’s crust). Barium and strontium are also common in nature, accounting for 0.05 and 0.034% of the mass of the earth's crust, respectively. Beryllium is a rare element, the amount of which is 6·10−4% of the mass of the earth's crust. As for radium, which is radioactive, it is the rarest of all alkaline earth metals, but it is always found in small quantities in uranium ores. in particular, it can be isolated from there chemically. Its content is 1·10−10% (of the mass of the earth's crust).
Biological role
Magnesium is found in the tissues of animals and plants (chlorophyll), is a cofactor in many enzymatic reactions, is necessary in the synthesis of ATP, is involved in the transmission of nerve impulses, and is actively used in medicine (bischophytotherapy, etc.). Calcium is a common macronutrient in the body of plants, animals and humans. In the human body and other vertebrates, most of it is found in the skeleton and teeth. bones contain calcium in the form of hydroxyapatite. The “skeletons” of most groups of invertebrates (sponges, coral polyps, mollusks, etc.) are made from various forms of calcium carbonate (lime). Calcium ions are involved in blood clotting processes, and also serve as one of the universal second messengers inside cells and regulate a variety of intracellular processes - muscle contraction, exocytosis, including the secretion of hormones and neurotransmitters. Strontium can replace calcium in natural tissues, since it is similar in properties to it. In the human body, the mass of strontium is about 1% of the mass of calcium.
At the moment, nothing is known about the biological role of beryllium, barium and radium. All compounds of barium and beryllium are poisonous. Radium is extremely radiotoxic. In the body, it behaves like calcium - about 80% of radium entering the body accumulates in bone tissue. Large concentrations of radium cause osteoporosis, spontaneous bone fractures and malignant tumors of bones and hematopoietic tissue. Radon, a gaseous radioactive decay product of radium, also poses a danger.
Notes
- According to the new IUPAC classification. According to the outdated classification, they belong to the main subgroup of group II of the periodic table.
- Nomenclature of Inorganic Chemistry. IUPAC Recommendations 2005. - International Union of Pure and Applied Chemistry, 2005. - P. 51.
- Group 2 - Alkaline Earth Metals, Royal Society of Chemistry.
- Gold fund. School encyclopedia. Chemistry. M.: Bustard, 2003.
| Periodic table of chemical elements by D. I. Mendeleev | ||||||||||||||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | |||||||||||||||
| 1 | H | He | ||||||||||||||||||||||||||||||
| 2 | Li | Be | B | C | N | O | F | Ne | ||||||||||||||||||||||||
| 3 | Na | Mg | Al | Si | P | S | Cl | Ar | ||||||||||||||||||||||||
| 4 | K | Ca | Sc | Ti | V | Cr | Mn | Fe | Co | Ni | Cu | Zn | Ga | Ge | As | Se | Br | Kr | ||||||||||||||
| 5 | Rb | Sr | Y | Zr | Nb | Mo | Tc | Ru | Rh | Pd | Ag | Cd | In | Sn | Sb | Te | I | Xe | ||||||||||||||
| 6 | Cs | Ba | La | Ce | Pr | Nd | Pm | Sm | Eu | Gd | Tb | Dy | Ho | Er | Tm | Yb | Lu | Hf | Ta | W | Re | Os | Ir | Pt | Au | Hg | Tl | Pb | Bi | Po | At | Rn |
| 7 | Fr | Ra | Ac | Th | Pa | U | Np | Pu | Am | Cm | Bk | Cf | Es | Fm | MD | No | Lr | Rf | Db | Sg | Bh | Hs | Mt | Ds | Rg | Cn | Uut | Fl | Uup | Lv | Uus | Uuo |
| 8 | Uue | Ubn | Ubu | Ubb | Ubt | Ubq | UBP | Ubh | ||||||||||||||||||||||||
alkaline earth metals in, alkaline earth metals and, alkaline earth metals chemistry, alkaline earth metals
The second group of D.I. Mendeleev’s periodic table contains a group of elements that are very similar in their properties to alkali metals, but are inferior to them in activity. It includes beryllium and magnesium, as well as calcium, strontium, barium and radium. They are known collectively as alkaline earth elements. In our article we will get acquainted with their distribution in nature and use in industry, and also study the most important chemical properties of alkaline earth metals.
general characteristics
All atoms of the above elements contain two electrons in their outer energy layer. When interacting with other substances, they always give up their negative particles, turning into the state of cations with a charge of 2+. In redox reactions, elements behave as strong reducing agents. As the nuclear charge increases, the chemical properties of alkaline earth metals and their activity increase. In air they quickly oxidize, forming an oxide film on their surface. The general formula of all oxides is RO. They correspond to hydroxides with the formula R(OH) 2. Their basic properties and solubility in water also increase with increasing atomic number of the element.
Special properties of beryllium and magnesium
In some of their properties, the first two representatives of the main subgroup of the second group are somewhat different from other alkaline earth elements. This manifests itself, in particular, during their interaction with water. For example, the chemical properties of beryllium are such that it does not react at all with H 2 O. Magnesium reacts with water only when heated. But all alkaline earth elements easily react with it at ordinary temperatures. What substances are formed in this case?
Alkaline earth metal bases
Being active elements, calcium, barium and other representatives of the group quickly displace hydrogen from water, resulting in their hydroxides. The interaction of alkaline earth metals with water proceeds violently, with the release of heat. Solutions of calcium, barium, and strontium bases are soapy to the touch and cause severe burns if they come into contact with the skin and mucous membrane of the eyes. The first aid in such cases will be to treat the wound surface with a weak solution of acetic acid. It will neutralize alkali and reduce the risk of necrosis of damaged tissue.
Chemical properties of alkaline earth metals
Interaction with oxygen, water and non-metals is the main list of properties of metals included in the second group of the periodic table of chemical elements. For example, calcium, even under normal conditions, reacts with halogens: fluorine, chlorine, bromine and iodine. When heated, it combines with sulfur, carbon and nitrogen. Hard oxidation - combustion, ends with the formation of calcium oxide: 2Ca + O 2 = 2 CaO. The interaction of metals with hydrogen leads to the appearance of hydrides. They are white, refractory substances with ionic crystal lattices. Important chemical properties of alkaline earth metals include their interaction with water. As stated earlier, the product of this displacement reaction will be a metal hydroxide. We also note that in the main subgroup of the second group, calcium occupies the most significant place. Therefore, let us dwell on its characteristics in more detail.
Calcium and its compounds
The content of the element in the earth's crust is up to 3.5%, which indicates its widespread occurrence in minerals such as limestone, chalk, marble and calcite. Natural calcium contains six types of isotopes. It is also found in natural water sources. Alkali metal compounds are studied in detail in the course of inorganic chemistry. For example, in 9th grade lessons, students learn that calcium is a light but strong silvery-white metal. Its melting and boiling points are higher than those of alkaline elements. The main method of production is electrolysis of a mixture of molten salts of calcium chloride and calcium fluoride. The main chemical properties include its reactions with oxygen, water and non-metals. Of the alkali metal compounds, calcium oxide and base are the most important for industry. The first compound is obtained from chalk or limestone by burning them.
Next, calcium hydroxide is formed from calcium oxide and water. Its mixture with sand and water is called mortar. It continues to be used as plaster and for joining bricks when laying walls. A calcium hydroxide solution called limewater is used as a reagent to detect carbon dioxide. When carbon dioxide is passed through a clear aqueous solution of Ca(OH) 2, it becomes cloudy due to the formation of an insoluble precipitate of calcium carbonate.
Magnesium and its characteristics
The chemistry of alkaline earth metals studies the properties of magnesium, focusing on some of its features. It is a very light, silvery-white metal. Magnesium, molten in an atmosphere with high humidity, actively absorbs hydrogen molecules from water vapor. As the metal cools, it almost completely releases them back into the air. It reacts very slowly with water due to the formation of a slightly soluble compound - magnesium hydroxide. Alkalis have no effect on magnesium at all. The metal does not react with some acids: concentrated sulfate and hydrofluoric acids, due to its passivation and the formation of a protective film on the surface. Most mineral acids dissolve the metal, which is accompanied by the rapid release of hydrogen. Magnesium is a strong reducing agent; it replaces many metals from their oxides or salts:
BeO + Mg = MgO + Be.
The metal, together with beryllium, manganese, and aluminum, is used as an alloying additive to steel. Magnesium-containing alloys - electrons - have especially valuable properties. They are used in aircraft and automobile production, as well as in parts of optical equipment.
The role of elements in the life of organisms
Let us give examples of alkaline earth metals, the compounds of which are common in living nature. Magnesium is the central atom in chlorophyll molecules in plants. It is involved in the process of photosynthesis and is part of the active centers of green pigment. Magnesium atoms capture light energy, then converting it into the energy of chemical bonds of organic compounds: glucose, amino acids, glycerol and fatty acids. The element plays an important role as a necessary component of enzymes that regulate metabolism in the human body. Calcium is a macroelement that ensures the effective passage of electrical impulses through nerve tissue. The presence of its phosphoric acid salts in bones and tooth enamel gives them hardness and strength.
Beryllium and its properties
Alkaline earth metals also include beryllium, barium and strontium. Consider beryllium. The element is not very common in nature; it is mainly found in minerals, such as beryl. Its varieties containing multi-colored impurities form precious stones: emeralds and aquamarines. The peculiarity of the physical properties is fragility and high hardness. A distinctive feature of the element’s atom is the presence on the second outer energy level of not eight, like all other alkaline earth metals, but only two electrons.
Therefore, the radius of the atom and ion is disproportionately small, and the ionization energy is high. This determines the high strength of the metal crystal lattice. The chemical properties of beryllium also distinguish it from other elements of the second group. It reacts not only with acids, but also with alkali solutions, displacing hydrogen and forming hydroxoberyllates:
Be + 2NaOH + 2H 2 O = Na 2 + H 2.
The metal has a number of unique characteristics. Due to its ability to transmit x-rays, it is used to make windows for x-ray tubes. In the nuclear industry, the element is considered the best moderator and reflector of neutrons. In metallurgy, it is used as a valuable alloying additive that increases the anti-corrosion properties of alloys.
Strontium and barium
The elements are quite common in nature and, like the alkaline earth metal magnesium, are found in minerals. Let's call them: barite, celestine, strontianite. Barium has the appearance of a ductile metal with a silvery-white color. Like calcium, it is represented by several isotopes. In air, it actively interacts with its components - oxygen and nitrogen, forming barium oxide and nitride. For this reason, the metal is stored under a layer of paraffin or mineral oil, avoiding its contact with air. Both metals form peroxides when heated to 500°C.
Of these, barium peroxide has practical application, used as a fabric bleach. The chemical properties of the alkaline earth metals barium and strontium are similar to those of calcium. However, their interaction with water is much more active, and the resulting bases are stronger than calcium hydroxide. Barium is used as an additive to liquid metal coolants that reduces corrosion, in optics, and in the manufacture of vacuum electronic devices. Strontium is in demand in the production of photocells and phosphors.
Qualitative reactions using alkaline earth metal ions
Barium and strontium compounds are examples of alkaline earth metals widely used in pyrotechnics due to the bright coloring of the flame by their ions. Thus, strontium sulfate or carbonate gives a carmine-red glow of the flame, and the corresponding barium compounds give a yellow-green glow. To detect calcium ions in the laboratory, several grains of calcium chloride are poured onto the burner flame; the flame turns brick-red.
A solution of barium chloride is used in analytical chemistry to identify ions of the acidic residue of sulfate acid in a solution. If, when the solutions are drained, a white precipitate of barium sulfate is formed, it means that there were SO 4 2- particles in it.
In our article, we studied the properties of alkaline earth metals and gave examples of their use in various industries.
The concept of alkaline earth metals includes part of the elements of group II of the periodic system: beryllium, magnesium, calcium, strontium, barium, radium. The last four metals have the most pronounced signs of the alkaline earth classification, therefore, in some sources, beryllium and magnesium are not included in the list, limiting themselves to four elements.
The metal got its name due to the fact that when their oxides interact with water, an alkaline environment is formed. Physical properties of alkaline earth metals: all elements have a gray metallic color, under normal conditions they have a solid structure, with increasing atomic number their density increases, and have a very high melting point. Unlike alkali metals, elements of this group cannot be cut with a knife (with the exception of strontium). Chemical properties of alkaline earth metals: they have two valence electrons, activity increases with increasing atomic number, and act as a reducing agent in reactions.
The characteristics of alkaline earth metals indicate their high activity. This especially applies to elements with a large serial number. For example, beryllium under normal conditions does not interact with oxygen and halogens. To trigger the reaction mechanism, it must be heated to a temperature of over 600 degrees Celsius. Magnesium under normal conditions has an oxide film on the surface and also does not react with oxygen. Calcium oxidizes, but rather slowly. But strontium, barium and radium oxidize almost instantly, so they are stored in an oxygen-free environment under a kerosene layer.
All oxides increase their basic properties with increasing atomic number of the metal. Beryllium hydroxide is an amphoteric compound that does not react with water, but is highly soluble in acids. Magnesium hydroxide is a weak alkali, insoluble in water, but reactive with strong acids. Calcium hydroxide is a strong, slightly water-soluble base that reacts with acids. Barium and strontium hydroxides are strong bases that are highly soluble in water. And radium hydroxide is one of the strongest alkalis that reacts well with water and almost all types of acids.
Methods of obtaining
Alkaline earth metal hydroxides are prepared by exposing the pure element to water. The reaction proceeds at room conditions (except for beryllium, which requires an increase in temperature) with the evolution of hydrogen. When heated, all alkaline earth metals react with halogens. The resulting compounds are used in the production of a wide range of products from chemical fertilizers to ultra-precision microprocessor parts. Alkaline earth metal compounds exhibit the same high activity as pure elements, which is why they are used in many chemical reactions.
Most often this occurs during exchange reactions, when it is necessary to displace a less active metal from a substance. They take part in redox reactions as a strong reducing agent. Divalent cations of calcium and magnesium give water so-called hardness. Overcoming this phenomenon occurs by precipitating ions using physical action or adding special softening substances to the water. Alkaline earth metal salts are formed by dissolving elements in acid or as a result of exchange reactions. The resulting compounds have a strong covalent bond and therefore have low electrical conductivity.
In nature, alkaline earth metals cannot be found in pure form, since they quickly interact with the environment, forming chemical compounds. They are part of minerals and rocks contained in the thickness of the earth's crust. The most common is calcium, followed by magnesium, and barium and strontium are quite common. Beryllium is a rare metal, and radium is a very rare metal. In all the time that has passed since the discovery of radium, only one and a half kilograms of pure metal have been mined all over the world. Like most radioactive elements, radium has isotopes, of which there are four.
Alkaline earth metals are obtained by decomposing complex substances and isolating pure substances from them. Beryllium is mined by reducing it from fluoride under high temperature. Barium is reduced from its oxide. Calcium, magnesium and strontium are obtained by electrolysis of their chloride melt. The most difficult thing to synthesize is pure radium. It is mined by exposure to uranium ore. According to scientists, on average there are 3 grams of pure radium per ton of ore, although there are also rich deposits that contain as much as 25 grams per ton. To isolate the metal, methods of precipitation, fractional crystallization and ion exchange are used.
Applications of alkaline earth metals
The range of applications of alkaline earth metals is very wide and covers many industries. Beryllium is in most cases used as an alloying additive in various alloys. It increases the hardness and strength of materials, and protects the surface well from corrosion. Also, due to its weak absorption of radioactive radiation, beryllium is used in the manufacture of X-ray machines and in nuclear energy.
Magnesium is used as one of the reducing agents in the production of titanium. Its alloys are characterized by high strength and lightness, therefore they are used in the production of aircraft, cars, and rockets. Magnesium oxide burns with a bright, blinding flame, which is reflected in military applications where it is used to make incendiary and tracer rounds, flares and flash-bang grenades. It is one of the most important elements for regulating the normal functioning of the body, therefore it is included in some medicines.
Calcium in its pure form is practically not used. It is needed for the recovery of other metals from their compounds, as well as in the production of drugs to strengthen bone tissue. Strontium is used to reduce other metals and as a major component for the production of superconducting materials. Barium is added to many alloys that are designed to work in aggressive environments, as it has excellent protective properties. Radium is used in medicine for short-term irradiation of the skin in the treatment of malignant tumors.
Properties of alkaline earth metals
Physical properties
Alkaline earth metals (compared to alkali metals) have higher temperatures. and boiling point, ionization potentials, densities and hardness.
Chemical properties
1. Very reactive.
2. They have a positive valence of +2.
3. React with water at room temperature (except Be) to release hydrogen.
4. They have a high affinity for oxygen (reducing agents).
5. With hydrogen they form salt-like hydrides EH 2.
6. Oxides have the general formula EO. The tendency to form peroxides is less pronounced than for alkali metals.
Being in nature
3BeO ∙ Al 2 O 3 ∙ 6SiO 2 beryl
Mg
MgCO 3 magnesite
CaCO 3 ∙ MgCO 3 dolomite
KCl ∙ MgSO 4 ∙ 3H 2 O kainite
KCl ∙ MgCl 2 ∙ 6H 2 O carnallite
CaCO 3 calcite (limestone, marble, etc.)
Ca 3 (PO 4) 2 apatite, phosphorite
CaSO 4 ∙ 2H 2 O gypsum
CaSO 4 anhydrite
CaF 2 fluorspar (fluorite)
SrSO 4 celestine
SrCO 3 strontianite
BaSO 4 barite
BaCO 3 witherite
Receipt
Beryllium is obtained by reduction of fluoride:
BeF 2 + Mg═ t ═ Be + MgF 2
Barium is obtained by reduction of the oxide:
3BaO + 2Al═ t ═ 3Ba + Al 2 O 3
The remaining metals are obtained by electrolysis of chloride melts:
CaCl 2 = Ca + Cl 2 ╜
cathode: Ca 2+ + 2ē = Ca 0
anode: 2Cl - - 2ē = Cl 0 2
MgO + C = Mg + CO
Metals of the main subgroup of group II are strong reducing agents; compounds exhibit only the +2 oxidation state. The activity of metals and their reducing ability increases in the series: Be Mg Ca Sr Ba╝
1. Reaction with water.
Under normal conditions, the surface of Be and Mg is covered with an inert oxide film, so they are resistant to water. In contrast, Ca, Sr and Ba dissolve in water to form hydroxides, which are strong bases:
Mg + 2H 2 O═ t ═ Mg(OH) 2 + H 2
Ca + 2H 2 O = Ca(OH) 2 + H 2 ╜
2. Reaction with oxygen.
All metals form oxides RO, barium peroxide BaO 2:
2Mg + O2 = 2MgO
Ba + O 2 = BaO 2
3. Binary compounds are formed with other non-metals:
Be + Cl 2 = BeCl 2 (halides)
Ba + S = BaS (sulfides)
3Mg + N 2 = Mg 3 N 2 (nitrides)
Ca + H 2 = CaH 2 (hydrides)
Ca + 2C = CaC 2 (carbides)
3Ba + 2P = Ba 3 P 2 (phosphides)
Beryllium and magnesium react relatively slowly with non-metals.
4. All metals dissolve in acids:
Ca + 2HCl = CaCl 2 + H 2 ╜
Mg + H 2 SO 4 (diluted) = MgSO 4 + H 2 ╜
Beryllium also dissolves in aqueous solutions of alkalis:
Be + 2NaOH + 2H 2 O = Na 2 + H 2 ╜
5. Qualitative reaction to cations of alkaline earth metals - coloring of the flame in the following colors:
Ca 2+ - dark orange
Sr 2+ - dark red
Ba 2+ - light green
The Ba 2+ cation is usually discovered by an exchange reaction with sulfuric acid or its salts:
Barium sulfate is a white precipitate, insoluble in mineral acids.
Alkaline earth metal oxides
Receipt
1) Oxidation of metals (except Ba, which forms peroxide)
2) Thermal decomposition of nitrates or carbonates
CaCO 3 ═ t ═ CaO + CO 2 ╜
2Mg(NO 3) 2 ═ t ═ 2MgO + 4NO 2 ╜ + O 2 ╜
Chemical properties
Typical basic oxides. Reacts with water (except BeO), acid oxides and acids
MgO + H 2 O = Mg(OH) 2
3CaO + P 2 O 5 = Ca 3 (PO 4) 2
BeO + 2HNO 3 = Be(NO 3) 2 + H 2 O
BeO is an amphoteric oxide, soluble in alkalis:
BeO + 2NaOH + H 2 O = Na 2
Alkaline earth metal hydroxides R(OH) 2
Receipt
Reactions of alkaline earth metals or their oxides with water: Ba + 2H 2 O = Ba(OH) 2 + H 2
CaO(quicklime) + H 2 O = Ca(OH) 2 (slaked lime)
Chemical properties
Hydroxides R(OH) 2 are white crystalline substances, less soluble in water than hydroxides of alkali metals (the solubility of hydroxides decreases with decreasing atomic number; Be(OH) 2 is insoluble in water, soluble in alkalis). The basicity of R(OH) 2 increases with increasing atomic number:
Be(OH) 2 - amphoteric hydroxide
Mg(OH) 2 - weak base
the remaining hydroxides are strong bases (alkalis).
1) Reactions with acid oxides:
Ca(OH) 2 + SO 2 = CaSO 3 ¯ + H 2 O
Ba(OH) 2 + CO 2 = BaCO 3 ¯ + H 2 O
2) Reactions with acids:
Mg(OH) 2 + 2CH 3 COOH = (CH 3 COO) 2 Mg + 2H 2 O
Ba(OH) 2 + 2HNO 3 = Ba(NO 3) 2 + 2H 2 O
3) Exchange reactions with salts:
Ba(OH) 2 + K 2 SO 4 = BaSO 4 ¯+ 2KOH
4) Reaction of beryllium hydroxide with alkalis:
Be(OH) 2 + 2NaOH = Na 2
Hardness of water
Natural water containing Ca 2+ and Mg 2+ ions is called hard water. Hard water forms scale when boiled and food products cannot be cooked in it; Detergents do not produce foam.
Carbonate (temporary) hardness is caused by the presence of calcium and magnesium bicarbonates in water, non-carbonate (permanent) hardness is caused by chlorides and sulfates.
The total hardness of water is considered as the sum of carbonate and non-carbonate.
Water hardness is removed by precipitation of Ca 2+ and Mg 2+ ions from solution:
1) boiling:
Сa(HCO 3) 2 ═ t ═ CaCO 3 ¯ + CO 2 + H 2 O
Mg(HCO 3) 2 ═ t═ MgCO 3 ¯ + CO 2 + H 2 O
2) adding lime milk:
Ca(HCO 3) 2 + Ca(OH) 2 = 2CaCO 3 ¯ + 2H 2 O
3) adding soda:
Ca(HCO 3) 2 + Na 2 CO 3 = CaCO 3 ¯+ 2NaHCO 3
CaSO 4 + Na 2 CO 3 = CaCO 3 ¯ + Na 2 SO 4
MgCl 2 + Na 2 CO 3 = MgCO 3 ¯ + 2NaCl
To remove temporary hardness, all four methods are used, and for permanent hardness, only the last two are used.
Thermal decomposition of nitrates.
E(NO3)2 =t= EO + 2NO2 + 1/2O2
Features of the chemistry of beryllium.
Be(OH)2 + 2NaOH (g) = Na2
Al(OH)3 + 3NaOH (g) = Na3
Be + 2NaOH + 2H2O = Na2 + H2
Al + 3NaOH + 3H2O = Na3 + 3/2H2
Be, Al + HNO3 (Conc) = passivation
