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Post topic: Introduction of carbon element?
Landlord: shaoys? [2006-3- 18? Afternoon? 02:49:53]
Introduction of carbon element
Carbon, carbon, comes from carbo, which is charcoal. This substance was discovered long ago. The picture above shows its three natural forms: diamond, charcoal and stone black. Countless carbon compounds are indispensable substances in our daily life. Products range from nylon and gasoline, perfume and plastics to shoe polish, DDT and explosives.
A brief history of the discovery of carbon
Carbon can be said to be one of the earliest elements that human beings came into contact with and used. Since human beings appeared on the earth, they have been in contact with carbon. Because lightning burning wood will leave charcoal, after animals are burned to death, bone carbon will remain. After human beings learned to make a fire, carbon became a permanent "partner" of human beings, so carbon is an element that has been known since ancient times. The exact date of carbon discovery cannot be verified, but from lavoisier? Answer? l？ From the table of elements compiled by1743-1794 France) 1789, it can be seen that carbon appears as an element. Carbon played an important role in the development of ancient phlogiston theory. According to this theory, carbon is not an element, but a pure phlogiston. Because he studied the combustion of coal and other chemicals, lavoisier first pointed out that carbon is an element.
There are three kinds of carbon allotropes in nature-diamond, graphite and C60. Diamond and graphite have long been known. After burning diamond and graphite, lavoisier determined that both substances would produce CO2, and concluded that diamond and graphite contain the same "basis", that is, carbon. Lavoisier is the first country to list carbon in the periodic table of elements. C60 was discovered in 1985 by the chemist Harry Kraut of Rice University in Houston, USA. It is a spherical stable carbon molecule composed of 60 carbon atoms, and it is the third allotrope of carbon, second only to diamond and graphite.
The Latin name of Carbon comes from the word carbon, which means "coal". It first appeared in the book Chemical Nomenclature edited by lavoisier and others in 1787. The English name of carbon is Corbon.
Elemental carbon
The mass fraction of carbon in the crust is 0.027%, which is widely distributed in nature. Carbon in the form of compounds includes coal, oil, natural gas, animals and plants, limestone, dolomite, carbon dioxide and so on.
By the end of 1998, the total number of compounds registered in American Chemical Abstracts, the largest chemical abstract in the world, was18.8 million, most of which were carbon compounds.
As we all know, amino acids and nucleotides, the basic units of life, are made of carbon as the skeleton. First, a carbon chain was extended and evolved into protein and nucleic acid; Then evolved into primitive single cells, and then evolved into insects, fish, birds, beasts, monkeys, orangutans, and even humans. The theme of this symphony of three or four billion years of life is the chemical evolution of carbon. It can be said that there is no life without carbon. Carbon is the pillar of the life world.
There are three kinds of pure carbon, namely diamond, graphite and C60. They are three allotropes of carbon.
diamond
graphite
Carbon sixty
diamond
Diamond is the hardest mineral in nature, because it is crystal-clear and beautiful and dazzling. It is the hardest of all substances. The characterization method for measuring the hardness of substances stipulates that the hardness of diamond is 10 to measure the hardness of other substances. For example, the hardness of chromium is 9, that of iron is 4.5, that of lead is 1.5 and that of sodium is 0.4. Among all simple substances, its melting point is the highest, reaching 3823K K.
Diamond crystal belongs to cubic crystal system and is a typical atomic crystal. Each carbon atom forms a valence bond with four other carbon atoms through sp3 hybrid orbitals, forming a regular tetrahedron. This is the structure of diamond face-centered cubic cell.
Because the C-C bond in diamond crystal is very strong, all valence electrons participate in the formation of valence bond, and there are no free electrons in the crystal, so diamond is not only hard, but also has a high melting point and is not conductive.
At room temperature, diamonds are inert to all chemical reagents, but when heated to about 1 100K in air, they can be burned into CO2.
Diamonds, commonly known as diamonds, are not only used for decoration, but also mainly used for manufacturing drills and abrasives. It is an important modern industrial raw material, and its price is very expensive.
graphite
Graphite is black and soft, and it is the softest ore in the world. The density of graphite is lower than that of diamond, and its melting point is only 50K lower than that of diamond, which is 3773K.
In graphite crystals, carbon atoms form * * * valence single bonds with three adjacent carbon atoms through sp2 hybrid orbitals, forming a hexagonal network structure, and these network structures are connected into a sheet structure. Each carbon atom in the layer maintains a P orbit that does not participate in sp2 hybridization, and has an unpaired P electron. The m electrons in this carbon atom in the same layer form a large bond (bond) of the m electrons in the m center. These delocalized electrons can move in the whole plane layer of carbon atoms, so graphite has good electrical and thermal conductivity in the layer direction.
The layers of graphite are bonded together by intermolecular forces, so graphite is easy to slide and crack in the direction parallel to the layers. Graphite is soft and smooth.
Because there are free electrons in the graphite layer, the chemical properties of graphite are slightly more active than that of diamond.
Graphite is widely used to make electrodes, high-temperature thermocouples, crucibles, brushes, lubricants and pencil lead, because it has electrical conductivity, chemical inertness, high temperature resistance and is easy to form and process.
Carbon sixty
In the mid-1980s, the third allotrope of carbon, C60, was discovered. We introduce C60 from the following three aspects.
Discovery of carbon sixty and its structural characteristics
Preparation of C60
The use of carbon sixty
Discovery of carbon sixty and its structural characteristics
199610/On October 7th, the Scientific Committee of the Royal Swedish Academy decided to award1996 the Nobel Prize in Chemistry to Robert? FCurl, Jr (USA), Harold? WKroto (UK) and Richard? Esmali (USA) discovered C60.
1At the beginning of September, 1995, Kroto et al. conducted a laser gasification experiment of graphite in order to simulate the formation process of carbon clusters in the atmosphere near the N-type red giant. They found from the obtained mass spectrum that there are a series of molecules composed of even carbon atoms, one of which is 20-25 times stronger than other peaks, and the mass number of this peak corresponds to a molecule composed of 60 carbon atoms.
What kind of structural stability is C60 molecule? Layered graphite and tetrahedral diamond are two stable forms of carbon. When 60 carbon atoms are arranged in any one of them, there will be many dangling bonds, which will be very active and will not show such a stable mass spectrum signal. This shows that C60 molecule has a completely different structure from graphite and diamond. Due to the influence of architect Buckminster? Inspired by Fuller's arched dome building composed of pentagons and hexagons, clotho and others think that C60 is a spherical 32-sided body composed of 60 carbon atoms, that is, it is composed of 12 pentagons and 20 hexagons. Only in this way can C60 molecules have no dangling bonds.
In C60 molecule, each carbon atom is connected with three adjacent carbon atoms through sp2 hybridization orbitals, and the remaining P orbitals that do not participate in hybridization form spherical bonds at the periphery and inner cavity of C60 spherical shell, thus having aromaticity. To commemorate Fuller, they proposed to name C60 after Buckminster fullerene. Later, all molecules including C60 with even carbon number were called Fuller, which was translated into Fullerene in Chinese.
Preparation of C60
When pure graphite is used as electrode, it is discharged in helium atmosphere, and the smoke and dust generated in the arc are deposited on the inner wall of water-cooled reactor. This soot contains a mixture of carbon atoms such as C60 and C70.
Separation and purification of fullerenes from soot by extraction. Put the ash into Soxhlet extractor and extract it with toluene or benzene. The main components in the extract are C60 and C70, and a small amount of C84 and C78. Pure C60 solution can be obtained by separating the extract by liquid chromatography. The C60 solution is purplish red, and dark red C60 microcrystals can be obtained by evaporating the solvent.
The use of carbon sixty
Since the discovery of C60 for more than ten years, fullerenes have widely influenced physics, chemistry, materials science, electronics, biology and medicine, greatly enriched and perfected scientific theories, and also showed great potential application prospects.
It is reported that C60 molecules are doped, so that C60 molecules capture other atoms or groups inside or outside their cages, forming C60-like derivatives. For example, C60F60 is to fully fluorinate C60 molecules, add fluorine atoms to the C60 spherical surface, and "lock" all electrons in the C60 spherical shell, so as not to combine with other molecules. Therefore, C60F60 shows that it is not easy to adhere to other substances, and its lubricity is better than C60. It can be used as an ultra-high temperature resistant lubricant and is regarded as a "molecular ball". For another example, doping metal atoms such as K, Cs and Tl into the cage of C60 molecules can make it have superconducting properties. The motor made of this material can keep the rotor rotating with little electricity. In addition, C60H60 is a hydrocarbon with relatively large molecular weight and extremely high calorific value, which can be used as rocket fuel. Wait a minute.
Bonding characteristics of carbon
Carbon belongs to the first element of group Ⅳ A in the periodic table of elements, and it is located between the halogen element with the strongest nonmetal and the alkali metal with the strongest metallicity. Its valence electron shell structure is 2s22p2. In chemical reactions, it is not easy to lose and gain electrons, and it is also difficult to form ionic bonds, but to form unique valence bonds, the highest valence of which is obviously 4.
Carbon atom sp3 hybridization
Sp2 hybridization of carbon atoms
Carbon atom sp hybridization-1
Carbon atom sp hybrid -2
Carbon atom sp3 hybridization
Sp3 hybridization of carbon atoms can generate four δ bonds, forming a regular tetrahedron configuration. Such as diamond, methane CH4, carbon tetrachloride CCl4, ethane C2H6, etc.
In methane molecule, four sp3 hybrid orbitals of C atom and four H atoms generate four δ * * * valence bonds, and the molecular configuration is regular tetrahedron structure.
Sp2 hybridization of carbon atoms
The Sp2 hybridization of carbon atoms produces three δ bonds, 1 ∏ bonds, and the plane triangle configuration. Such as graphite, COCl2, C2H4, C6H6, etc.
In COCl2 _ 2 molecule, C atom forms 1 Δ * * valence bond with two Cl atoms and 1 o atoms respectively through three sp2 hybridization orbitals, and the P electron on1p orbitals forms a ∏ * * valence bond with the unpaired P electron O atom in the P orbitals that did not participate in hybridization, so
Carbon atom sp hybridization-1
Two δ bonds and two ∏ bonds are generated and the configuration is linear. Such as CO2, HCN, C2H2, etc.
In CO2 molecule, C atom forms two δ * * valence bonds with two O atoms through two sp hybrid orbitals, and two P electrons on two non-hybrid P orbitals and three P electrons on two O atoms symmetric two P orbitals form two large ∏ bonds with three centers and four electrons, so CO2 is two double bonds.
In HCN molecule, C atom forms a 1 δ * * * valence bond with H atom and N atom respectively, and also forms two normal ∏ * * valence bonds with N atom, so it is a single bond of 1 triple bond in HCN molecule.
Carbon atom sp hybrid -2
The 1 δ bond, 1 ∏ bond, 1 coordination ∏ bond and 1 lone pair pair are generated, and the configurations are linear. For example, in the CO molecule, apart from generating a δ * * * valence bond and 1 normal ∏ * * valence bonds, the 1 empty P orbitals in which the C atom is not involved in hybridization can accept a pair of lone electron pairs from the O atom to form coordination bonds, so there are three bonds between C and O in the CO molecule.
Carbon atoms can form not only single bonds, double bonds and triple bonds, but also long straight chains, cyclic chains and branched chains. Criss-crossing, endless changes, together with hydrogen, oxygen, sulfur, phosphorus and metal atoms, constitute a wide variety of carbon compounds.
carbon dioxide
CO2 is a colorless and odorless gas, accounting for about 0.03% in the atmosphere and 0.0 14% in the ocean. It also exists in volcanic jet gas and some springs. The CO2 gas on the ground mainly comes from the combustion of carbon-containing compounds such as coal, oil and natural gas, the decomposition of calcium carbonate ore, the respiration and fermentation of animals. When sunlight passes through the atmosphere, CO2 absorbs infrared rays with the wavelength of 13~ 17nm, just like covering the earth with a huge plastic film, so that the warm infrared rays are not lost and the earth becomes a greenhouse with a small temperature difference between day and night. The greenhouse effect of carbon dioxide provides a comfortable living environment for life. It also provides the basic substance of life and is the raw material of photosynthesis of green plants. Every year, through photosynthesis, green plants transform 15? 000 billion tons of carbon, converted into cellulose, starch and protein, and released O2 gas for animals and human consumption.
Green plants have always maintained the balance of O2 and CO2 in the atmosphere, but in recent years, with the rapid development of world industry and the resulting marine pollution, there are more and more CO2 in the atmosphere, which is estimated to increase by 2 to 4 million per year. This is considered to be an important factor affecting the general rise of world temperature.
About CO2, we introduce it from its structure, properties and preparation:
Structure of carbon dioxide
Properties of carbon dioxide
Preparation of carbon dioxide
Structure of carbon dioxide
In CO2 molecules, carbon atoms combine with oxygen atoms through sp hybrid orbitals.
Two sp hybrid orbitals of c atom generate two δ bonds with an o atom respectively. The two unhybridized P orbitals on the C atom are at right angles to the sp hybrid orbitals, and overlap with the P orbitals of the oxygen atom side by side, respectively, forming two delocalized bonds with three centers and four electrons. Therefore, the distance between carbon and oxygen atoms is shortened, and the carbon-oxygen bond in CO2 has a certain degree of triple bond characteristics. The molecular shape is determined by sp hybrid orbitals, and CO2 is a linear molecule.
Properties of carbon dioxide
CO2 molecules have no polarity, so the intermolecular force is small, the boiling point is low, the bond energy is large, the interatomic interaction is strong, and the molecular thermal stability is high. For example, at 2273K, CO2 only decomposes 1.8%:
CO2 has a high critical temperature and is easy to liquefy under pressure. The vaporization heat of liquid CO2 is very high, which is 25.1kj mol-1at 2 17K. When liquid CO2 evaporates freely, a part of CO2 condenses into snowflake-like solid, commonly known as "dry ice". This is a molecular crystal. Under normal pressure, dry ice is directly sublimated and gasified at 194.5K, so it is often used as refrigerant.
CO2 is an acidic oxide, which can react with alkali. In industry, the production of soda ash Na2CO3, baking soda NaHCO3, ammonium bicarbonate NH4HCO3, lead white pigment Pb (OH) 22pcbco3, beer, beverages, dry ice, etc. all consume a lot of CO2.
Generally speaking, CO2 does not support combustion. When the CO2 content in the air reaches 2.5%, the flame will go out. Therefore, CO2 is a widely used fire extinguishing agent. However, the burning magnesium strip can continue to burn in CO2 gas, which shows that it is relative that CO2 does not support combustion.
CO2 is inactive, but it can react with active metals such as carbon, magnesium and lead at high temperature.
Although CO2 is non-toxic, if the content in the air is too high, people will suffocate due to lack of oxygen. When entering the cellar, people should hold a burning candle. If the candle goes out, it means that the CO2 concentration in the cellar is too high, so it is not suitable to enter for the time being.
Preparation of carbon dioxide
Calcined limestone can be used to produce lime in industry, and a large amount of CO2 by-products can be obtained in wine-making industry.
In the laboratory, carbonate and hydrochloric acid are usually used to prepare CO2:
carbon monoxide
Carbon monoxide is also a colorless and odorless gas. Its structure, properties and preparation method are introduced.
corporate organization
Properties of carbon monoxide
Preparation of carbon monoxide
corporate organization
According to the hybrid orbital theory, in CO molecules, carbon atoms are bonded to oxygen atoms by sp hybridization.
Two P electrons of C atom can form a δ bond and an ω bond with two single P electrons of O atom, and the paired P electrons of O atom can also form a coordination bond with an empty 2p orbit of C atom. Definition of coordination bond: the valence bond formed by the use of an electron pair provided by one atom by two atoms is called coordination bond. ← indicates the coordination bond, and the arrow points to the atom accepting the electron pair. Here, the bonded electron pair is only provided by O atom, and C atom provides an empty orbit to accept electrons. Its structural formula can be expressed as:
According to the molecular orbital theory, it can be seen from the molecular orbital energy level diagram of CO molecule that there are four valence electrons outside the C nucleus, and their electronic structural formula is 2s22p2；; There are six valence electrons outside the O nucleus, and its electronic structural formula is 2s22p4. Because the atomic orbital energies of C atom and O atom are similar, they overlap each other to form the molecular orbital of CO molecule. The valence bond structure of CO molecule can be expressed as:
[1] The arrow in the formula indicates that oxygen unilaterally provides two atoms with a valence bond formed by a pair of electrons, which is also called coordination bond.
In formula [2], the coordination bond is ∏, and the two points are on one side, indicating that the electron is in the orbit of the oxygen atom when it is in the atomic state, and it is still relatively close to the oxygen nucleus after the formation of the CO molecule.
This triple bond structure containing coordination bonds can satisfactorily explain the fact that the bond energy is large, the bond length and dipole moment are almost equal to zero. If there is no coordination bond, CO should be a very polar molecule, because the electronegativity of O atom is much greater than that of C atom, but the existence of coordination bond makes O atom slightly positive and C atom slightly negative, and the two factors cancel each other out, so the dipole moment of CO is almost equal to zero.
There are 10 valence electrons in CO molecule and N2 molecule respectively. They are isoelectronic bodies, also known as isoelectronic molecules. The orbital electron arrangement and bonding properties of isoelectronic molecules are very similar.
In the CO molecule, because the C atom has a slight negative charge, it is easier for this C atom to provide electron pairs to other atoms with empty orbitals, form coordination bonds, and generate many carbonyl compounds. This is one reason why the bond energy of CO molecule is more active than that of N2 molecule.
Properties of carbon monoxide
(1) and carbon monoxide are good reducing agents.
At high temperature, CO can obtain oxygen from many metal oxides and reduce metals. Using coke as reducing agent in metallurgical industry is actually harmful to co;
At room temperature, CO can also reduce metal ions in some compounds. For example, CO can blacken palladium dichloride solution and silver ammonia solution, and the reaction is very sensitive, which can be used to detect the existence of trace CO;
Cobalt is an important ligand and can form metal carbonyl compounds with many transition metals. Such as Fe(CO)5, Ni(CO)4 and Cr(CO)6. We take Ni(CO)4 as an example to illustrate the bonding characteristics of carbonyl compounds.
In metal carbonyl compounds, co is connected with metal by C. From the energy level diagram of molecular orbital of CO, we already know that, on the one hand, CO has non-bonded electron pairs (lone electron pairs), which can give metal atoms an empty orbit and form a δ coordination bond. On the other hand, there is an empty anti-bond ∏ channel in CO, which can accept the D electron pair of metal atoms and overlap with the D orbit of metal atoms to form a ∏ bond. This ∏ bond is called a feedback bond or a coordination bond, because the metal atom unilaterally provides an electron pair to the empty orbit of the ligand (CO). Feedback bond can just reduce the accumulation of excessive negative charges on metal atoms caused by the formation of δ coordination bond.
Among carbonyl compounds, the metal is in a low oxidation state and has more valence electrons, which is beneficial to the formation of feedback bonds. For example, in Ni(CO)4, the valence of Ni atom is zero, and the valence electron is 3d84s2. Ni atom adopts sp3 hybrid orbital to accept four non-bond electron pairs provided by CO to form a δ coordination bond. In addition, the D electron pair on the Ni atom is fed back to the empty anti-bond ∏ * orbit of CO, resulting in a feedback bond. Because δ coordination bond and feedback bond are bonded at the same time, carbonyl compounds generated by metal and CO have high stability.
Carbonyl compounds are usually highly toxic. The high toxicity of CO to animals and humans also comes from its addition. It can combine with heme (an iron complex) in blood to produce carbonyl compounds, which makes blood lose the function of transporting oxygen and leads to tissue hypoxia. If 50% of heme in blood is combined with CO, it will cause myocardial necrosis. As long as there is 1/800 volume ratio of CO in the air, it can kill people within half an hour. ( 1aroman？ CO is quite active and easily combines with O, S, H and halogens F2, Cl2 and Br2.
(1) Carbon monoxide will burn in the air, producing carbon dioxide and releasing a lot of heat;
② Carbon monoxide reacts with H2 to produce methanol and some organic compounds;
③CO reacts with S to produce carbonyl sulfur;
④CO reacts with halogens F2, Cl2 and Br2 to generate carbonyl halide, which is easily decomposed by water and reacts with ammonia to generate urea;
Carbonyl chloride, also known as phosgene, is extremely toxic. However, its output is very large, and it is used to make toluene diisocyanate, which is an intermediate in the production of polyurethane plastics.
Preparation of carbon monoxide
Methods of preparing carbon monoxide gas in laboratory;
(1), dropping formic acid into hot concentrated sulfuric acid for dehydration;
(2) heating oxalic acid crystals with concentrated sulfuric acid;
The mixed gas produced by the reaction absorbs CO2 through solid NaOH to obtain pure CO gas.
Industrial preparation method of carbon monoxide gas;
The main sources of industrial CO are water gas, producer gas and coal gas.
The equimolecular mixture of water gas CO and H2 is obtained when air and steam are alternately introduced into the red-hot carbon layer.
Producer gas is a mixture of CO and N2 (CO accounts for half of the volume), which is obtained by a limited amount of air through red-hot carbon layer reaction.
The gas is a mixture of carbon monoxide, H2, methane and carbon dioxide. Water gas, producer gas and coal gas are all important industrial gas fuels.
Carbonic acid and carbonate
CO2 can be dissolved in water to form H2CO3 carbonate, which is a weak acid and only exists in aqueous solution, and its pH value is about 4.
H2CO3 is a dibasic acid, which can generate carbonate and bicarbonate.
Among these two ions, C atom forms four bonds with four foreign electrons by using sp2 hybrid orbitals, and the ions are planar triangles. It is important to know the solubility, hydrolysis and thermal stability of these two salts in water.
solubility
hydrolyze
thermostability
solubility
Carbonate: Carbonate of ammonium and alkali metals (except lithium) is easily soluble in water. Carbonates of other metals are insoluble in water. For example, (NH4)2CO3, Na2CO3 and K2CO3 are soluble in water, while CaCO3 and MgCO3 are insoluble in water.
Bicarbonate: For insoluble carbonate, the corresponding bicarbonate has great solubility. For example, insoluble calcium carbonate ore can be partially transformed into Ca(HCO3)2 and dissolved under the long-term erosion of CO2 and water;
For soluble carbonate, its corresponding bicarbonate has relatively low solubility. For example, when CO2 is pumped into the concentrated ammonium carbonate solution until it is saturated, NH4HCO3 can be precipitated, which is the basis for industrial production of ammonium bicarbonate fertilizer.
The abnormal solubility is related to the formation of dimeric or polymeric chains of HCO3- ions through hydrogen bonds:
hydrolyze
Carbonate and bicarbonate of alkali metals and ammonium are strongly alkaline and weakly alkaline respectively due to hydrolysis in aqueous solution.
In the solution of metal salts (except alkali metals and ammonium salts)? CO32- ion, the product may be carbonate, basic carbonate or hydroxide, which product is it? Generally speaking:
(1) strongly alkaline hydroxide ions, that is, metal ions that do not hydrolyze, can precipitate into carbonate. For example:
(2) Weak basic ions of hydroxide, such as Cu2+, Zn2+, Pb2+, Mg2+, etc. Its solubility is similar to carbonate, and it can be precipitated into basic carbonate. For example:
(3) Highly hydrolyzable metal ions, especially zwitterions with small solubility product of hydroxide, such as Al3+, Cr3+, Fe3+, etc. , will precipitate into hydroxide. For example:
Therefore, sodium carbonate and ammonium carbonate are often used as precipitants for metal ions.
thermostability
Thermal instability is an important property of carbonate. Generally speaking, the following thermal stability order exists:
Alkali metal carbonate >: alkaline earth metal carbonate >: carbonate of sub-group elements and transition elements.
Among alkali metals and alkaline earth metals, carbonate with large cation radius is larger than carbonate with small cation radius.
The difficulty of decomposing carbonate by heating is also related to the polarization of cations.