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Boron group elements

This is a mind map about boron family elements. The main content includes: elements of boron family elements, aluminum compounds, aluminum compounds, etc.

Edited at 2024-03-05 10:33:24

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Boron group elements

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Boron group elements

Aluminum compounds

In aluminum compounds, the oxidation number of aluminum is generally +3. Aluminum compounds are available in both covalent and ionic forms.

Due to the large number of AI + charges, the radius is small ( r =53

It forms ionic compounds with those anions that are difficult to deform (such as F,02-); and forms covalent compounds with those anions that are more easily deformed (such as CI, Br, I). The covalent compounds of aluminum have a low melting point, are volatile, and can be dissolved in organic solvents; the ionic compounds of aluminum have a high melting point and are insoluble in organic solvents.

Alumina

Aluminum hydroxide

Aluminum halide

Aluminum can form aluminum halide AIX3. Except for AIF, which is an ionic compound, other AIX3 are covalent compounds. The properties of AIF3 are also quite special. It is a white insoluble solid (its solubility is 0.56g/100gH20), and Other AIX3s are easily soluble in water. In AIF, in the crystal, the coordination number of AI is 6, and the gaseous AIF3 is a single molecule.

Among the aluminum halides, AICI3 is the most important. Due to hydrolysis of aluminum salt solution, anhydrous AICI3 cannot be produced in aqueous solution. Dissolve aluminum in hydrochloric acid, and what is separated is colorless, hygroscopic hydrated crystal AICI3·6H20. Anhydrous AICI3 can be obtained by heating metallic aluminum in a stream of chlorine or hydrogen chloride:

Anhydrous AICI3 can also be prepared by passing chlorine gas into the mixture of red-hot AI203 and carbon:

Anhydrous AICI3 is a colorless crystal at room temperature, but it often appears yellow due to the presence of FeCI3. Anhydrous AICI is soluble in organic solvents and has high solubility in water. Its hydrolysis reaction is very violent and releases a lot of heat, even in humid air it smokes due to strong hydrolysis. Anhydrous AICI3 is easily volatile.

The aluminum atom in the AICI3 molecule is an electron-deficient atom, so AICI, a typical Lewis acid, shows a strong tendency for addition. In the gaseous state, 2 AICI molecules aggregate into bimeric molecules AI, CI.

In addition to polymerizing into dimer molecules, AICI3 can also add to Lewis bases such as organic amines, ethers, and alcohols.

Oxylate of aluminum

Al ions can form some relatively stable complexes, The most industrially important aluminum salts are aluminum sulfate and alum. They are used as sizing materials in the paper industry, and are added to paper pulp together with sodium resinate to bond fibers; they can also be used to purify water, because the hydroxides they react with water have strong adsorption properties; Aluminum sulfate or alum is also used as a mordant in the printing and dyeing industry.

Boron compounds

Judging from the bonding characteristics of the boron element, there are four types of boron compounds:

(1) Boron forms covalent compounds with elements that are more electronegative than it, such as BF3 and BCI3. In this type of compound, boron atoms form o bonds with atoms of other elements in sp2 hybrid orbitals, and the spatial configuration of the molecule is a flat triangle.

(2) Form four-coordinate compounds through coordination bonds, such as [BF4], etc. Since boron is an electron-deficient atom, in a three-position boron compound, after the boron atom forms three covalent bonds with atoms of other elements, a p orbital is left vacant. Therefore, it can also accept a pair of electrons from other negative ions or molecules. Form a matching key. When forming a bond, boron atoms form bonds in hybrid orbitals, and their spatial configuration is tetrahedral.

(3) Boron and hydrogen form electron-deficient compounds containing three-center bonds (hydrogen bridges), such as B and H. and BH etc. (see hydrides for details). This is also determined by the electron-deficient characteristics of boron atoms.

(4) Boron and active metals form compounds with an oxidation value of -3, such as Mg3B2, etc.

Among boron compounds, important ones include boron hydrides, oxygen-containing compounds and halides.

boron hydride

Borane can form a series of covalent hydrides with hydrogen, also known as borane. Borane is extremely toxic. Simple borane is a colorless gas with an unpleasant odor and is extremely toxic.

A hydrogen bridge is different from a hydrogen bond. It is a special covalent bond that reflects the electron-deficient characteristics of boron-hydrogen compounds.

1. Normally, borane is very unstable, easily combustible in air, and can even spontaneously ignite, and the reaction rate is high. 2. Borane and water undergo different degrees of hydrolysis, and the reaction rates are also different. 3. Borane acts as a Lewis acid. , can undergo addition reaction with molecules with lone pairs of electrons such as CO, NH3, etc. 4. Diborane reacts directly with LiH and NaH in diethyl ether to generate LiBH4 and NaBH4 (excellent reducing agent for organic synthesis

Oxygen compounds of boron

Boron trioxide (B2O3)

Boric acid (H3BO3, HBO2, xB2O3·yH2O)

monobasic weak acid

Borate

The most important borate is sodium tetraborate, commonly known as borax. The molecular formula of borax is Na2B4O5(OH)4`.H2O, which is also commonly written as Na2B4O7.10H20.

Molten borax can dissolve many metal oxides to form double salts of metaboric acid. Metaborate double salts of different metals exhibit different characteristic colors. For example:

Na2B4O7 CoO → Co (BO2)2.2NaBO2 (blue)

Na2B4O 7 NiO → Ni (BO2)2.2NaBO2 (brown)

The above reaction can be regarded as a process in which the acidic oxide B2O reacts with the alkaline metal oxide to form metaborate. This type of reaction of borax can be used to identify the ionization of certain metals, which is called the borax bead test in analytical chemistry.

Borax is easily soluble in water, and its solution becomes alkaline due to hydrolysis.

At 20°C, the pH of the borax solution is 9.24. Borax solution can be used in the laboratory to prepare buffer solutions.

Borax is used in the ceramic industry to prepare low melting point glazes. Borax is also used to make special glasses that are resistant to sudden temperature changes

Boron halide

BX3

The molecular configuration of boron trihalide is a planar triangle. In the BX3 molecule, the boron atom forms a б bond with the halogen atom in the SP2 hybrid orbit. As the radius of the halogen atom increases, the bond energy of the B—X bond↓

Boron trihalide molecules are covalent. At room temperature, as the relative molecular mass increases, the existence state of BX 3 transitions from gaseous BF 3 and BCI 3 to liquid BBr 3 to solid BI3. Pure BX 3 is colorless, but BBr3 and BI3 partially decompose under light and appear yellow.

BX 3 smokes due to hydrolysis in humid air: BX 3 is an electron-deficient compound with the ability to accept lone pairs of electrons, thus exhibiting the formation of adducts between Lewis and Lewis bases (such as ammonia, ether, etc.) Boron trifluoride is hydrolyzed to produce boric acid and hydrofluoric acid, and BF3 is added to the generated HF to produce fluoroboric acid.

Fluoboric acid is a strong acid, more acidic than hydrofluoric acid. Except for BF 3, other boron trihalides generally do not add with the corresponding halogen acid to form BX4. This is because the radius of the central boron atom is very small, and as the radius of the halogen atom increases, it becomes more difficult to accommodate four larger atoms around the boron atom. Although BX 3 is an electron-deficient compound, it cannot form dimer molecules, unlike aluminum halides. BX 3 reacts with alkali metals and alkaline earth metals to be reduced to elemental boron The most important among BX3 are BF3 and BCI3, which are catalysts for many organic reactions and are also commonly used in the synthesis of organoboron compounds and the preparation of boron hydride compounds.

Boron nitride

Boron nitride BN is a new type of inorganic synthetic material. In the laboratory, pure BN is prepared by melting borax and ammonium chloride; boron trichloride reacts with excess ammonia, and the product is thermally decomposed to produce BN.

BN and CO have the same number of atoms and electrons - isoelectronic bodies. Isoelectronic bodies often show similar structures and similar properties.

BN has three crystal forms: amorphous (similar to amorphous carbon), hexagonal (similar to graphite), and cubic (similar to diamond).

Hexagonal BN, also known as white graphite, is an excellent high-temperature-resistant lubricant. The boron nitride fiber made with it is soft in texture and is not eroded by inorganic solvents. It is light, fireproof, high-temperature resistant, and corrosion-resistant. and other characteristics, have been used in industry. Cubic crystal boron nitride, with a hardness similar to diamond, used as an abrasive

elements of the boron family

boron

The content of boron in the earth's crust is very small, and it mainly exists in the form of oxygen-containing compounds in nature.

Elemental boron has various allotropes such as amorphous boron and crystalline boron. Amorphous boron is brown powder, and crystalline boron is black gray. Boron has a very high melting and boiling point. Crystalline boron is very hard.

Boron has a strong ability to absorb neutrons and is used as a good neutron absorber in nuclear reactors. Boron is also used as a raw material to prepare some special boron compounds

aluminum

Aluminum is widely distributed in nature, mainly in the form of bauxite (Al2O3·xH2O) mineral

Aluminum is a silver-white, shiny light metal with good electrical conductivity and ductility.

Thermite reaction: A large amount of heat is released when aluminum combines with oxygen, which is related to the large lattice energy of Al2O3. Therefore, aluminum can reduce most metal oxides to elemental substances. When a mixture of certain metal oxides and aluminum powder is burned, a violent reaction of aluminum reducing metal oxides occurs, and the corresponding metal element is obtained, and a large amount of heat is released.

Gallium, Indium, Thallium

Gallium, indium, and thallium do not exist as separate minerals in nature, but are dispersed in other minerals in the form of impurities.

Gallium, indium, and thallium are all soft metals with similar physical properties and low melting points. The melting point of gallium is lower than human body temperature.

Gallium, indium and thallium can be used to produce new semiconductor materials, such as gallium arsenide, which is an important semiconductor material