ORBITAL
ORBITAL, in ELEMENTARY PARTICLE PHYSICS - the surface of space around the atomic NUCLEUS in which ELECTRONS can move. There is a high probability of the presence of an electron in such an orbital. It may contain one or two electrons. The orbital has a shape and energy corresponding to the QUANTUM NUMBER of the atom. In molecules, bond electrons move in the combined electric field of all nuclei. In this case, atomic orbitals become molecular orbitals, regions that surround two nuclei that have a characteristic energy and contain two electrons. These molecular orbitals, formed from atomic orbitals, constitute CHEMICAL BONDS.
Atomic orbitals describe the surface around the nucleus of an atom, which most likely contains electrons. They can also be called "energy clouds". Their existence explains chemical bonds. Electrons are contained within atomic or molecular structures arranged into energy levels. The first level is characterized by only one type of electron: it has one s-orbital (A), shown relative to the x, y and z axes of the atom. The maximum number of electrons that can be in this energy level is two. For the second type of electrons, the orbital has the shape of two connected spheres located symmetrically relative to the nucleus. Such an orbital is called a p-orbital (B) V atom three such orbitals, and they are located at right angles to each other (1,2, 3) Orbitals that have regular spherical shapes are conventionally designated as pear-shaped clouds for clarity of the picture . In addition, there are also five d-orbitals (C-G), each of which consists of four pear-shaped lobes on two perpendicular axes, intersecting at the G nucleus - a combination of two p-orbitals.
Scientific and technical encyclopedic dictionary.
See what "ORBITAL" is in other dictionaries:
Orbital: Atomic orbital. Molecular orbital. A list of meanings of a word or phrase with links to relevant articles. If you came here from... Wikipedia
orbital- – a complete set of wave functions of an electron located in the field of nuclides and the averaged field of all other electrons interacting with the same nuclides. Atomic orbital is the allowed state of an electron in an atom, a geometric image,... ... Chemical terms
A function of spatial variables of one electron, which has the meaning of a wave function of an electron located in the field of an atomic or molecular core. If such a function takes into account the spin electron, then it is called. spin O. For more details, see Molecular orbital... ... Physical encyclopedia
orbital- orbitale. physical Atomic and molecular wave functions of an electron located in the field of one or more atomic nuclei and in the average field of all other electrons of the atom or molecule in question. NES 2000… Historical Dictionary of Gallicisms of the Russian Language
- (from lat. orbita path, track), wave function describing the state of one electron in an atom, molecule or other quantum system. In the general case, quantum chemistry. the term O. is used for any function that depends on the variables x, y, z of one ... ... Chemical encyclopedia
orbital- orbitalė statusas T sritis chemija apibrėžtis Banginė funkcija, apibūdinanti elektrono judėjimą atome arba molekulėje; erdvė, kurioje elektrono buvimas labiausiai tikėtinas. atitikmenys: engl. orbital rus. orbital... Chemijos terminų aiškinamasis žodynas
orbital- orbitalė statusas T sritis fizika atitikmenys: engl. orbital vok. Orbital, n rus. orbital, f pranc. orbitale, f … Fizikos terminų žodynas
orbital- orbit al, and... Russian spelling dictionary
orbital- With. Orbit buencha bashkaryl torgan. Orbit buencha hәrәkәt itә torgan yaki shunyn өchen bilgelәngәn… Tatar telen anlatmaly suzlege
orbital- A function of spatial variables of one electron, which has the meaning of the wave function of an individual electron in the field of the effective atomic or molecular core ... Polytechnic terminological explanatory dictionary
Books
- Set of tables. Chemistry. Structure of matter (10 tables), . Educational album of 10 sheets. The structure of the atom. Electron orbital. Models of atoms of some elements. Crystals. Chemical bond. Valence. Oxidation state. Isometrics. Homology. Art...
Composition of the atom.
An atom is made up of atomic nucleus And electron shell.
The nucleus of an atom consists of protons ( p+) and neutrons ( n 0). Most hydrogen atoms have a nucleus consisting of one proton.
Number of protons N(p+) is equal to the nuclear charge ( Z) and the ordinal number of the element in the natural series of elements (and in the periodic table of elements).
N(p +) = Z
Sum of neutrons N(n 0), denoted simply by the letter N, and number of protons Z called mass number and is designated by the letter A.
A = Z + N
The electron shell of an atom consists of electrons moving around the nucleus ( e -).
Number of electrons N(e-) in the electron shell of a neutral atom is equal to the number of protons Z at its core.
The mass of a proton is approximately equal to the mass of a neutron and 1840 times the mass of an electron, so the mass of an atom is almost equal to the mass of the nucleus.
The shape of the atom is spherical. The radius of the nucleus is approximately 100,000 times smaller than the radius of the atom.
Chemical element- type of atoms (collection of atoms) with the same nuclear charge (with the same number of protons in the nucleus).
Isotope- a collection of atoms of the same element with the same number of neutrons in the nucleus (or a type of atom with the same number of protons and the same number of neutrons in the nucleus).
Different isotopes differ from each other in the number of neutrons in the nuclei of their atoms.
Designation of an individual atom or isotope: (E - element symbol), for example: .
Structure of the electron shell of an atom
Atomic orbital- state of an electron in an atom. The symbol for the orbital is . Each orbital has a corresponding electron cloud.
Orbitals of real atoms in the ground (unexcited) state are of four types: s, p, d And f.
Electronic cloud- the part of space in which an electron can be found with a probability of 90 (or more) percent.
Note: sometimes the concepts of “atomic orbital” and “electron cloud” are not distinguished, calling both “atomic orbital”.
The electron shell of an atom is layered. Electronic layer formed by electron clouds of the same size. The orbitals of one layer form electronic ("energy") level, their energies are the same for the hydrogen atom, but different for other atoms.
Orbitals of the same type are grouped into electronic (energy) sublevels:
s-sublevel (consists of one s-orbitals), symbol - .
p-sublevel (consists of three p
d-sublevel (consists of five d-orbitals), symbol - .
f-sublevel (consists of seven f-orbitals), symbol - .
The energies of orbitals of the same sublevel are the same.
When designating sublevels, the number of the layer (electronic level) is added to the sublevel symbol, for example: 2 s, 3p, 5d means s-sublevel of the second level, p-sublevel of the third level, d-sublevel of the fifth level.
The total number of sublevels at one level is equal to the level number n. The total number of orbitals at one level is equal to n 2. Accordingly, the total number of clouds in one layer is also equal to n 2 .
Designations: - free orbital (without electrons), - orbital with an unpaired electron, - orbital with an electron pair (with two electrons).
The order in which electrons fill the orbitals of an atom is determined by three laws of nature (the formulations are given in simplified terms):
1. The principle of least energy - electrons fill the orbitals in order of increasing energy of the orbitals.
2. The Pauli principle - there cannot be more than two electrons in one orbital.
3. Hund's rule - within a sublevel, electrons first fill empty orbitals (one at a time), and only after that they form electron pairs.
The total number of electrons in the electronic level (or electron layer) is 2 n 2 .
The distribution of sublevels by energy is expressed as follows (in order of increasing energy):
1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f, 6d, 7p ...
This sequence is clearly expressed by an energy diagram:
The distribution of an atom's electrons across levels, sublevels, and orbitals (electronic configuration of an atom) can be depicted as an electron formula, an energy diagram, or, more simply, as a diagram of electron layers ("electron diagram").
Examples of the electronic structure of atoms:
Valence electrons- electrons of an atom that can take part in the formation of chemical bonds. For any atom, these are all the outer electrons plus those pre-outer electrons whose energy is greater than that of the outer ones. For example: the Ca atom has 4 outer electrons s 2, they are also valence; the Fe atom has 4 outer electrons s 2 but he has 3 d 6, therefore the iron atom has 8 valence electrons. Valence electronic formula of the calcium atom is 4 s 2, and iron atoms - 4 s 2 3d 6 .
Periodic table of chemical elements by D. I. Mendeleev
(natural system of chemical elements)
Periodic law of chemical elements(modern formulation): the properties of chemical elements, as well as simple and complex substances formed by them, are periodically dependent on the value of the charge of atomic nuclei.
Periodic table- graphic expression of the periodic law.
Natural series of chemical elements- a series of chemical elements arranged according to the increasing number of protons in the nuclei of their atoms, or, what is the same, according to the increasing charges of the nuclei of these atoms. The atomic number of an element in this series is equal to the number of protons in the nucleus of any atom of this element.
The table of chemical elements is constructed by “cutting” the natural series of chemical elements into periods(horizontal rows of the table) and groupings (vertical columns of the table) of elements with a similar electronic structure of atoms.
Depending on the way you combine elements into groups, the table may be long-period(elements with the same number and type of valence electrons are collected into groups) and short period(elements with the same number of valence electrons are collected into groups).
The short-period table groups are divided into subgroups ( main And side), coinciding with the groups of the long-period table.
All atoms of elements of the same period have the same number of electron layers, equal to the period number.
Number of elements in periods: 2, 8, 8, 18, 18, 32, 32. Most of the elements of the eighth period were obtained artificially; the last elements of this period have not yet been synthesized. All periods except the first begin with an alkali metal-forming element (Li, Na, K, etc.) and end with a noble gas-forming element (He, Ne, Ar, Kr, etc.).
In the short-period table there are eight groups, each of which is divided into two subgroups (main and secondary), in the long-period table there are sixteen groups, which are numbered in Roman numerals with the letters A or B, for example: IA, IIIB, VIA, VIIB. Group IA of the long-period table corresponds to the main subgroup of the first group of the short-period table; group VIIB - secondary subgroup of the seventh group: the rest - similarly.
The characteristics of chemical elements naturally change in groups and periods.
In periods (with increasing serial number)
- nuclear charge increases
- the number of outer electrons increases,
- the radius of atoms decreases,
- the strength of the bond between electrons and the nucleus increases (ionization energy),
- electronegativity increases,
- the oxidizing properties of simple substances are enhanced ("non-metallicity"),
- the reducing properties of simple substances weaken ("metallicity"),
- weakens the basic character of hydroxides and corresponding oxides,
- the acidic character of hydroxides and corresponding oxides increases.
In groups (with increasing serial number)
- nuclear charge increases
- the radius of atoms increases (only in A-groups),
- the strength of the bond between electrons and the nucleus decreases (ionization energy; only in A-groups),
- electronegativity decreases (only in A-groups),
- the oxidizing properties of simple substances weaken ("non-metallicity"; only in A-groups),
- the reducing properties of simple substances are enhanced ("metallicity"; only in A-groups),
- the basic character of hydroxides and corresponding oxides increases (only in A-groups),
- weakens the acidic character of hydroxides and corresponding oxides (only in A-groups),
- the stability of hydrogen compounds decreases (their reducing activity increases; only in A-groups).
Tasks and tests on the topic "Topic 9. "Structure of the atom. Periodic law and periodic system of chemical elements by D. I. Mendeleev (PSHE) "."
- Periodic law - Periodic law and structure of atoms grades 8–9
You must know: the laws of filling orbitals with electrons (the principle of least energy, the Pauli principle, Hund's rule), the structure of the periodic table of elements.You must be able to: determine the composition of an atom by the position of the element in the periodic table, and, conversely, find an element in the periodic system, knowing its composition; depict the structure diagram, electronic configuration of an atom, ion, and, conversely, determine the position of a chemical element in the PSCE from the diagram and electronic configuration; characterize the element and the substances it forms according to its position in the PSCE; determine changes in the radius of atoms, properties of chemical elements and the substances they form within one period and one main subgroup of the periodic system.
Example 1. Determine the number of orbitals in the third electron level. What are these orbitals?
To determine the number of orbitals, we use the formula N orbitals = n 2 where n- level number. N orbitals = 3 2 = 9. One 3 s-, three 3 p- and five 3 d-orbitals.Example 2. Determine which element's atom has electronic formula 1 s 2 2s 2 2p 6 3s 2 3p 1 .
In order to determine what element it is, you need to find out its atomic number, which is equal to the total number of electrons of the atom. In this case: 2 + 2 + 6 + 2 + 1 = 13. This is aluminum.After making sure that everything you need has been learned, proceed to completing the tasks. We wish you success.
Recommended reading:- O. S. Gabrielyan and others. Chemistry 11th grade. M., Bustard, 2002;
- G. E. Rudzitis, F. G. Feldman. Chemistry 11th grade. M., Education, 2001.
General analytical expression for functions R(r), 0(0) and Ф(ф) are written using special mathematical functions. They can be found in specialized literature on quantum mechanics and quantum chemistry. In this section, using an example s-, p- and “/-electrons”, the main provisions adopted to describe electron orbitals, which are the basis of the theory of chemical bonds, will be considered.
From the results obtained earlier it follows that the description of the state of an electron in an atom turns out to be much more complex than assumed by Bohr's theory. Quantum mechanics shows that an atomic electron can be located in different regions of space surrounding the nucleus, and the probability of its presence changes from point to point. This is where the concept of electron orbitals arose, expressing the more general concept of an electron cloud. Physicists under electron orbital understand the wave function itself, corresponding to certain quantum numbers. In chemistry under orbital is understood as a set of positions of an electron in an atom, taking into account the probability of its presence in certain regions of space in the vicinity of the nucleus. This probability is determined by the functions R, 0, F. Table 8.2 shows expressions for wave functions in a spherical coordinate system s-,p- and "/-electrons.
Figure 8.21 shows the graphs of the functions R(r)(Fig. 8.21, A) and the probability density of detecting an electron in a spherical layer of thickness dr|^^ = 4nr 2 i? 2 (r)j - (Fig. 8.21, b) depending on the G. Should
pay attention to the fact that for j-states, the radial part of the wave function at g = 0 (those. on the core)(see function graphs R(r) in Fig. 8.21, A) have a maximum. No contradiction with common sense (an electron in the nucleus) arises in this case, since the function R(r) determines the probability density, and the probability itself
Table 8.2
Wave functions for S-, p- and "/-electrons
Ending
Note. The following designations are used in the table: a = (Z/a^rvL a 0 = Y 2 /(those 2) = = 0.5292 1(7 10 m - Bohr radius of the electron orbit of the hydrogen atom.
at T-> 0 (see the graph of the function 4лг 2 /? 2 (r) in Fig. 8.21, b) in the vicinity of the nucleus tends to zero.
Figure 8.22 shows a diagram for constructing graphs of the angular part of the wave function 7(0, a) and its square 7 2 (0, b) using the p r orbital as an example. The value 7(0, φ) for angle 0 is represented by the length of the segment OM. It is advisable to pay attention to the fact that the graph of function 7(0) is represented by spheres, while the graph of 7 2 (0) is represented by elongated “dumbbells”. So, in table. 8.2 the wave functions of the hydrogen atom were presented for n = 1, 2 and 3. The first row of this table shows data for the 15 state of the electron. In this case the function R(r) has a maximum at g = 0 and decreases exponentially with increasing r. The function 7(0, φ) does not depend on either 0 or φ, therefore the probability density distribution | y| 2 is spherically symmetrical. The same is true for 25- and 35-STATES.
Rice. 8.21. Radial part of wave functions R(r) (a) and values 4lg 2 L 2 (d) (b) for some electronic states
Rice. 8.22. Scheme for constructing graphs of the angular parts of the wave function Y(0,
Solutions for 2/b states x = 2, / = 0u1u/R/ = 0u ± 1 are given in the subsequent rows of the table. 8.2. Noteworthy is the fact that the solution for the p-orbital has a simpler form than for the orbitals p x And RU. This axis selection z associated with the nature of the spherical coordinate system (see Figure 8.16). In order to obtain the angular part of the wave function in real form and find a general analytical expression for the orbitals p x And RU, we must use the property that any linear combination of solutions to the Schrödinger equation is also a solution to this equation. Therefore, using Euler’s formula, it is necessary to create linear combinations of solutions Y, and Y 1; _ 1, giving real wave functions:
In this type of orbital p x And RU are presented in table. 8.2. They are widely used in chemistry. In the same way, the angular parts were obtained in real form for the ^/ states of electrons. Having determined the values of all parts of the wave function at point c g(g, 0,
In the absence of any external influence, when there is no reason to select a dedicated axis Oz, all solutions of the Schrödinger equation and all their linear combinations can take place. However, they have no physical meaning, because there is no way to check this: any attempt to establish the nature of the orbital will introduce a disturbance into the system and highlight the axis Oz. This also reveals a feature of quantum mechanics (as it turns out, a device for studying a state violates the very state of the object of study).
If the atom in question finds itself surrounded by other atoms, then the occurrence of interactions introduces significant changes in its energy state. Moreover, in different circumstances, other linear combinations of solutions may become more energetically favorable (for example, the well-known s-p and s-d-^-hybrid states, which are a superposition - a linear combination, given in table. 8.2 orbitals).
The probability of electrons staying in regions of space that are identical in volume, but at different points for the depicted orbitals, is different. It is extremely difficult to present atomic orbitals in a general form in a graphical, visual form. However, there are different ways to do this.
Everything becomes even more complicated when trying to depict the total wave function of an electron in an atom, which is the product. This method, in particular, presents the results of X-ray studies of the structure of molecules of chemical compounds in the scientific literature.
division of three functions, and its square modulus |y(r, 0, q) in the form of isolines, i.e. lines connecting points with the same values --- (following the example of well-known geographical maps). dV
Quantum chemistry also sometimes uses orbital graphs in the form of closed surfaces within which a certain amount (most often 90%) of the total electronic charge is contained. Figure 8.23 shows the orbitals for different states of the electron in the hydrogen atom. Noteworthy is the fact that the orbit
Rice. 8.23.
the hoists do not touch the zero point (the position of the core). This occurs because in this region, due to the radial part of the wave function, the probability density of detecting an electron is very small (almost zero probability of finding an electron in the nucleus).
Already for hydrogen-like atoms, not to mention more complex systems, atomic orbitals turn out to be much more complex. Unfortunately, it is not possible to obtain exact analytical solutions for such cases. Therefore, in quantum chemistry various types of modifications (approximations) are used that more or less adequately describe this or that system, this or that region of the atom. For example, in the exponent of the exponential characterizing the radial part of the wave function, a certain constant factor is introduced that describes the compression-expansion of the atom (Slater's factor). Sometimes for the radial function, not one, but the sum of two or several exponentials is used, each of which individually more accurately describes the distribution of electron density near the nucleus and far from it. These and other empirical modifications of the solution for different atoms are considered in quantum chemical applications.
- For heavy atoms, the probability of finding an electron inside the nucleus becomes significant. It is this that determines the nuclear transformation called K-capture - the capture of a K-shell electron by a nucleus, as a result of which a proton turns into a neutron, and the charge of the nucleus changes.
The electron has a dual nature: in different experiments it can exhibit the properties of a particle and a wave. Properties of the electron as a particle: mass, charge; wave properties- in the features of motion, interference and diffraction.
The movement of an electron obeys the laws quantum mechanics .
The main characteristics that determine the movement of an electron around the nucleus: energy and spatial features of the corresponding orbital.
When interacting (overlapping) atomic orbitals(JSC ) belonging to two or more atoms are formed molecular orbitals(MO).
Molecular orbitals are filled with shared electrons and carry out covalent bond.
Before the formation of molecular orbitals, there may be hybridization of atomic orbitals of one atom.
Hybridization – changing the shape of some orbitals during the formation of a covalent bond to more effectively overlap them. Identical hybrids are formed JSC who participate in education MO, overlapping the atomic orbitals of other atoms. Hybridization is possible only for atoms that form chemical bonds, but not for free atoms.
Hydrocarbons
Main questions:
- Hydrocarbons. Classification. Nomenclature.
- Structure. Properties.
- Application of hydrocarbons.
Hydrocarbons- a class of organic compounds that consist of two elements: carbon and hydrogen.
Select isomers and homologues:
Name the alkanes:
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__________________________________________
Ä nitration reaction (Konovalov reaction, 1889) is the reaction of hydrogen substitution with a nitro group.
Conditions: 13% HNO 3, t = 130 – 140 0 C, P = 15 – 10 5 Pa. On an industrial scale, nitration of alkanes is carried out in the gas phase at 150 – 170 0 C with nitrogen oxide (IV) or nitric acid vapor.
CH 4 + HO – NO 2 → CH 3 – NO 2 + H 2 O
nitromethane
@ Solve tasks:
1. The composition of alkanes is reflected by the general formula:
a) C n H 2 n +2; b) C n H 2 n -2; c) C n H 2 n; d) C n H 2 n -6 .
2. What reagents can alkanes react with:
A) Br 2 (solution); b) Br 2, t 0; V) H 2 SO 4; G) HNO 3 (diluted), t 0 ; d) KMnO 4 ; e) CON?
Answers: 1) reagents a, b, d, d; 2) reagents b, c, f;
3) reagents b, d; 4) reagents b, d, d, f.
- Establish a correspondence between the type of reaction and the reaction scheme (equation):
- Indicate the substance that is formed during complete chlorination of methane:
a) trichloromethane; b) carbon tetrachloride; c) dichloromethane; d) tetrachloroethane.
- Specify the most probable product of monobromination of 2,2,3-trimethylbutane:
a) 2-bromo-2,3,3-trimethylbutane; b) 1-bromo-2,2,3-trimethylbutane;
c) 1-bromo-2,3,3-trimethylbutane; d) 2-bromo-2,2,3-trimethylbutane.
Write an equation for the reaction.
Wurtz reaction – effect of metallic sodium on halogen derivatives of hydrocarbons. When two different halogen derivatives react, a mixture of hydrocarbons is formed, which can be separated by distillation.
| CH 3 I + 2 Na + CH 3 I → C 2 H 6 + 2 NaI |
@ Solve tasks:
1. Indicate the name of the hydrocarbon that is formed when bromoethane is heated with sodium metal:
a) propane; b) butane; c) pentane; d) hexane; e) heptane.
Write an equation for the reaction.
- What hydrocarbons are formed when metallic sodium acts on the mixture:
a) iodomethane and 1-bromo-2-methylpropane; b) 2-bromopropane and 2-bromobutane?
Cycloalkanes
1. For small cycles (C 3 – C 4) are characteristic addition reactions hydrogen, halogens and hydrogen halides. The reactions are accompanied by the opening of the cycle.
2. For other cycles (From 5 and above) typical substitution reactions.
Unsaturated hydrocarbons(unsaturated):
| Alkenes (olefins, unsaturated hydrocarbons with a double bond, ethylene hydrocarbons): Structure: sp 2 -hybridization, planar arrangement of orbitals (flat square). Reactions: addition (hydrogenation, halogenation, hydrohalogenation, polymerization), substitution (not typical), oxidation (combustion, KMnO 4), decomposition (without oxygen access). |  |
 |  |
 |  |
@ Solve tasks:
- What is the hybridization of carbon atoms in an alkene molecule:
a) 1 and 4 – sp 2, 2 and 3 – sp 3; b) 1 and 4 – sp 3, 2 and 3 – sp 2;
c) 1 and 4 – sp 3, 2 and 3 – sp; d) 1 and 4 – not hybridized, 2 and 3 – sp 2 .
2. Name the alkene:
- Draw up reaction equations using 1-butene as an example, and name the resulting products.
4. In the transformation scheme below, ethylene is formed in the reaction:
a) 1 and 2; b) 1 and 3; c) 2 and 3;
d) ethylene is not formed in any reaction.
- Which reaction goes against Markovnikov's rule:
a) CH 3 – CH = CH 2 + HBr →; b) CH 3 – CH = CH 2 + H 2 O →;;
c) CH 3 – CH = CH – CH 2 + HCI →; d) CCI 3 – CH = CH 2 + HCI →?
þ Dienes with conjugated bonds:hydrolysis 1,3-butadiene – 2-butene is formed (1,4-addition):
þ hydrogenation 1,3-butadiene in the presence of a catalyst Ni - butane:
þ halogenation 1,3-butadiene – 1,4-addition (1,4 – dibromo-2-butene):
þ polymerization of dienes:
Polyenes(unsaturated hydrocarbons with many double bonds) are hydrocarbons whose molecules contain at least three double bonds.
Preparation of dienes:
Ø effect of alcohol solution of alkali:
Ø Lebedev's method (divinyl synthesis):
Ø dehydration of glycols (alkanediols):
| Alkynes (acetylenic hydrocarbons, hydrocarbons with one triple bond): Structure: sp-hybridization, linear arrangement of orbitals. Reactions: addition (hydrogenation, halogenation, hydrohalogenation, polymerization), substitution (formation of salts), oxidation (combustion, KMnO 4), decomposition (without access of oxygen). |  5-methylhexine-2
1-pentine 3-methylbutine-1
|
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| 1. Which hydrocarbons correspond to the general formula C n H 2n-2: a) acetylene, diene; b) ethylene, diene; c) cycloalkanes, alkenes; d) acetylene, aromatic? 2. A triple bond is a combination of: a) threeσ bonds; b) one σ-bond and two π-bonds; c) two σ-bonds and one π-bond; d) threeπ bonds. 3. Create the formula for 3-methylpentine -3. | ||||
| I. Addition reactions | ||||
| v Hydrogenation occurs through the stage of formation of alkenes: | ||||
| v Addition of halogens occurs worse than in alkenes: Alkynes discolor bromine water ( qualitative reaction). | ||||
| v Addition of hydrogen halides: | ||||
| The addition products to unsymmetrical alkynes are determined Markovnikov's rule: | ||||
| v Adding water (hydration)– reaction of M.G. Kucherov, 1881. | ||||
| For acetylene homologues, the product of addition of water is a ketone: | ||||
| III. Formation of salts (acid properties) – substitution reactions | ||||
| ð Interaction with active metals: Acetylenides are used for the synthesis of homologues. | ||||
| ð Interaction of alkynes with ammonia solutions of silver oxide or copper(I) chloride: | ||||
| Qualitative reaction to the final triple bond - the formation of a grayish-white precipitate of silver acetylide or red-brown copper (I) acetylide: | HC ≡ CH + CuCI → CuC ≡ CCu ↓ + 2HCI No reaction occurs | |||
| IV. Oxidation reactions | ||||
| Mild oxidation– discoloration of an aqueous solution of potassium permanganate ( qualitative response to multiple connection): | When acetylene reacts with a dilute solution of KMnO 4 (room temperature) - oxalic acid. | |||
Orbitals exist regardless of whether an electron is present in them (occupied orbitals) or absent (vacant orbitals). The atom of each element, starting with hydrogen and ending with the last element obtained today, has a complete set of all orbitals at all electronic levels. They are filled with electrons as the atomic number, that is, the charge of the nucleus, increases.
s-Orbitals, as shown above, have a spherical shape and, therefore, the same electron density in the direction of each three-dimensional coordinate axis:
At the first electronic level of each atom there is only one s- orbital. Starting from the second electronic level in addition to s- three orbitals also appear R-orbitals. They are shaped like three-dimensional eights, this is what the area of the most likely location looks like R-electron in the region of the atomic nucleus. Each R-the orbital is located along one of three mutually perpendicular axes, in accordance with this in the name R-orbitals indicate, using the corresponding index, the axis along which its maximum electron density is located:
In modern chemistry, an orbital is a defining concept that allows us to consider the processes of formation of chemical bonds and analyze their properties, while attention is focused on the orbitals of those electrons that participate in the formation of chemical bonds, that is, valence electrons, usually the electrons of the last level.
The carbon atom in the initial state has two electrons in the second (last) electronic level. s-orbitals (marked in blue) and one electron in two R-orbitals (marked in red and yellow), the third orbital is p z-vacant:
Hybridization.
In the case when a carbon atom participates in the formation of saturated compounds (not containing multiple bonds), one s- orbital and three R-orbitals combine to form new orbitals that are hybrids of the original orbitals (the process is called hybridization). The number of hybrid orbitals is always equal to the number of original ones, in this case, four. The resulting hybrid orbitals are identical in shape and outwardly resemble asymmetrical three-dimensional figure eights:
The whole structure appears to be inscribed in a regular tetrahedron - a prism assembled from regular triangles. In this case, the hybrid orbitals are located along the axes of such a tetrahedron, the angle between any two axes is 109°. Carbon's four valence electrons are located in these hybrid orbitals:
Participation of orbitals in the formation of simple chemical bonds.
The properties of electrons located in four identical orbitals are equivalent; accordingly, the chemical bonds formed with the participation of these electrons when interacting with atoms of the same type will be equivalent.
The interaction of a carbon atom with four hydrogen atoms is accompanied by the mutual overlap of elongated hybrid orbitals of carbon with spherical orbitals of hydrogen. Each orbital contains one electron; as a result of overlap, each pair of electrons begins to move along the united molecular orbital.
Hybridization only leads to a change in the shape of the orbitals within one atom, and the overlap of the orbitals of two atoms (hybrid or ordinary) leads to the formation of a chemical bond between them. In this case ( cm. Figure below) the maximum electron density is located along the line connecting two atoms. Such a connection is called an s-connection.
Traditional writing of the structure of the resulting methane uses the valence bar symbol instead of overlapping orbitals. For a three-dimensional image of a structure, the valence directed from the drawing plane to the viewer is shown in the form of a solid wedge-shaped line, and the valence extending beyond the drawing plane is shown in the form of a dashed wedge-shaped line:
Thus, the structure of the methane molecule is determined by the geometry of the hybrid orbitals of carbon:
The formation of an ethane molecule is similar to the process shown above, the difference is that when the hybrid orbitals of two carbon atoms overlap, a C-C bond is formed:
The geometry of the ethane molecule resembles methane, bond angles are 109°, which is determined by the spatial arrangement of carbon hybrid orbitals:
Participation of orbitals in the formation of multiple chemical bonds.
The ethylene molecule is also formed with the participation of hybrid orbitals, but only one is involved in hybridization s-orbital and only two R-orbitals ( p x And RU), third orbital – p z, directed along the axis z, does not participate in the formation of hybrids. From the initial three orbitals, three hybrid orbitals arise, which are located in the same plane, forming a three-rayed star, the angles between the axes are 120°:
Two carbon atoms attach four hydrogen atoms and also connect to each other, forming a C-C s-bond:
Two orbitals p z, which did not participate in hybridization, overlap each other, their geometry is such that the overlap occurs not along the C-C communication line, but above and below it. As a result, two regions with increased electron density are formed, where two electrons (marked in blue and red) are located, participating in the formation of this bond. Thus, one molecular orbital is formed, consisting of two regions separated in space. A bond in which the maximum electron density is located outside the line connecting two atoms is called a p-bond:
The second valence feature in the designation of a double bond, which has been widely used to depict unsaturated compounds for centuries, in the modern understanding implies the presence of two regions with increased electron density located on opposite sides of the C-C bond line.
The structure of the ethylene molecule is determined by the geometry of hybrid orbitals, the H-C-H bond angle is 120°:
During the formation of acetylene, one s-orbital and one p x-orbital (orbitals p y And p z, do not participate in the formation of hybrids). The two resulting hybrid orbitals are located on the same line, along the axis X:
The overlap of hybrid orbitals with each other and with the orbitals of hydrogen atoms leads to the formation of C-C and C-H s-bonds, represented by a simple valence line:
Two pairs of remaining orbitals p y And p z overlap. In the figure below, colored arrows show that, from purely spatial considerations, the most likely overlap of orbitals with the same indices x-x And ooh. As a result, two p-bonds are formed surrounding a simple s-bond C-C:
As a result, the acetylene molecule has a rod-shaped shape:
In benzene, the molecular backbone is assembled from carbon atoms having hybrid orbitals composed of one s- and two R-orbitals arranged in the shape of a three-rayed star (like ethylene), R-orbitals not involved in hybridization are shown semi-transparent:
Vacant orbitals, that is, those not containing electrons (), can also participate in the formation of chemical bonds.
High level orbitals.
Starting from the fourth electronic level, atoms have five d-orbitals, their filling with electrons occurs in transition elements, starting with scandium. Four d-orbitals have the shape of three-dimensional quatrefoils, sometimes called “clover leaves”, they differ only in orientation in space, the fifth d-orbital is a three-dimensional figure eight threaded into a ring:
d-Orbitals can form hybrids with s- And p- orbitals. Options d-orbitals are usually used in the analysis of the structure and spectral properties of transition metal complexes.
Starting from the sixth electronic level, atoms have seven f-orbitals, their filling with electrons occurs in the atoms of lanthanides and actinides. f-Orbitals have a rather complex configuration; the figure below shows the shape of three of seven such orbitals, which have the same shape and are oriented in space in different ways:
f-Orbitals are very rarely used when discussing the properties of various compounds, since the electrons located on them practically do not take part in chemical transformations.
Prospects.
At the eighth electronic level there are nine g-orbitals. Elements containing electrons in these orbitals should appear in the eighth period, while they are not available (element No. 118, the last element of the seventh period of the Periodic Table, is expected to be obtained in the near future; its synthesis is carried out at the Joint Institute for Nuclear Research in Dubna).
Form g-orbitals, calculated by quantum chemistry methods, are even more complex than those of f-orbitals, the region of the most probable location of the electron in this case looks very bizarre. Below is the appearance of one of nine such orbitals:
In modern chemistry, concepts of atomic and molecular orbitals are widely used in describing the structure and reaction properties of compounds, also in analyzing the spectra of various molecules, and in some cases to predict the possibility of reactions occurring.
Mikhail Levitsky