What relationships are called multiples. Properties of covalent bond. Structure of ionic compounds
1.1.Simple (single) bond Types of bonds in bioorganic compounds.
Organic molecules are formed by covalent bonds. Covalent bonds occur between two atomic nuclei due to a common (socialized) pair of electrons. This method relates to the exchange mechanism. Non-polar and polar bonds are formed.
Lewis structure for compounds
View the Lewis diagram and learn how to draw the Lewis structural formula for joints. Learn how to represent single, double and triple bonds with lines instead of points. Also find out how connections are made. Lewis structures, as you learned, are a way to chart an element and easily show its valence electrons. In the structure of a Lewis point, the core of an element is represented by its symbol. Valence electrons are represented by dots arranged around the symbol in pairs.
This way, you can easily see when the valence shell of an element is not completely filled. You can also write Lewis structures for connections. If the nitrogen was combined with another nitrogen, the structure of the Lewis point would look like this. You can see that nitrogen has three pairs of electrons. Scientists are a bit lazy and do not want to do all these points, so instead they write a line between two characters, so it looks like this.
Non-polar bonds are characterized by a symmetric distribution of electron density between the two atoms that this bond connects.
Polar bonds are characterized by an asymmetric (non-uniform) distribution of electron density, it is shifted towards a more electronegative atom.
Rows of electronegativity (compiled downwards)
They leave extra points. They assume they are there; they are just too lazy to write them. Just remember that hydrogen is an exception to the rule and loves only two electrons in its outer shell. Structural formula is a way of displaying the location or ions relative to each other in a molecule, and also shows the number and location of the bonds between them. This can tell you a lot about the connection. He tells you which atoms are involved, the number of them, how they are arranged and the bonds between the atoms.
The steps for writing Lewis structures for connections are simple. Determine the type and number of atoms in the molecule. . Each hydrogen atom has one valence electron. Individually, they look like this. When they form a connection, they look like the image below. This structure is a stable hydrogen molecule, where both atoms share a pair of electrons.
A) Elements: F\u003e O\u003e N\u003e C1\u003e Br\u003e I ~~ S\u003e C\u003e H
B) carbon atom: C (sp)\u003e C (sp 2)\u003e C (sp 3)
Covalent bonds can be of two types: sigma (σ) and pi (π).
In organic molecules, sigma (σ) bonds are formed by electrons located on hybrid (hybridized) orbitals, the electron density is located between the atoms on the conventional line of their binding.
Chlorine has seven valence electrons. He likes to form relationships with himself. Often, scientists become lazy, throw extra points and just put a line on the bond. In this case, you place four dots between two letters or two lines to mark two bonds or two pairs of common electrons. The same goes for three or four pairs.
Four pairs, or bonds, are two different atoms. Connect atoms using electron pairs of bonds, so that each atom has a full octet. Double check your work and make sure that each atom has eight electrons and no more. You put C in the middle and form four complete bonds, one with each hydrogen atom.
- Write the structure of Lewis points for each individual atom.
- If you have carbon in a molecule, it is always in the middle.
- Hydrogens are usually outside.
π -connections (pi -connections) arise when two non-hybridized p-orbitals overlap. Their main axes are parallel to each other and perpendicular to the σ-link line. The combination of σ and π - bonds is called a double (multiple) bond, consists of two pairs of electrons. The triple bond consists of three pairs of electrons — one σ - and two π-bonds. (It is extremely rare in bioorganic compounds).
The Lewis point structure can be represented either by two points, or by a line between two atoms, when there is chemical bond - two lines for double bond and three lines for triple bond. You have learned that to write a Lewis structure for connections, you will follow these steps.
The bond of non-metal atoms in order to achieve a stable or low energy state. This happens when an atom of the main group has enough electrons to reach the shell with rare gases. Sometimes the number of electrons cannot be ensured by the exchange of electrons simply in single bonds.
σ -Connections are involved in the formation of the skeleton of the molecule, they are the main ones, and π -connections can be considered as additional, but giving special chemical properties to molecules.
1.2. Hybridization of carbon 6 orbitals
Electronic configuration of the unexcited state of the carbon atom
expressed by the electron distribution 1s 2 2s 2 2p 2.
Examples of this are nitrogen molecules. Nitrogen atoms have five valence electrons. If two nitrogen atoms simply form a single bond, the dotted structure will look like an illustrator below. Each nitrogen atom would have only six electrons, not an octet. A single bond does not provide two octet nitrogen atoms.
If you follow the octet rule, the nitrogen atoms should have more than two electrons. Trial and error is used to determine how many common electrons are needed to create a structure in which an octet rule is executed. Since one bond did not work, the next attempt to try is a double bond in which atoms share four electrons. Unfortunately, the structure of the double bond provides only 7 electrons of the valence shell, and not eight.
However, in bioorganic compounds, as indeed, in most inorganic substances, the carbon atom has a valence of four.
The transition of one of the 2s electrons to the free 2p orbital occurs. Excited states of the carbon atom arise, creating the possibility of the formation of three hybrid states, denoted as С sp 3, С sp 2, С sp.
Since single and double bonds did not do the trick, the next thing to try is a triple bond in which the nitrogen atoms share six electrons. The count for both atoms, when a triple bond is used in a structure, indicates that the octet rule is being fulfilled.
He was born in Portland, Oregon, in the year when his deep interest in chemistry dates back to his youth, a time when all the material related to the subject was absorbed by a young man who was eager for knowledge. After graduating from Oregon State University, Linus began to venture into the universe of chemistry, working on what will ultimately be that he leaves his biggest contribution: chemical bonds.
A hybrid orbital has characteristics different from “pure” s, p, d-orbitals and is a “mixture” of two or more types of non-hybridized orbitals..
Hybrid orbitals are characteristic of atoms only in molecules.
The concept of hybridization was introduced in 1931 by L.Poling, a Nobel Prize winner ,.
Consider the spatial arrangement of hybrid orbitals.
Another problem in which Pauling’s research turned out to be key is the study of benzene. Before Pauling's publications, science could not understand exactly how to link 6 carbon atoms and 6 hydrogen atoms, but Pauling suggested that this structure was based on a superposition of 2 structures: one with simple bonds and the other with double links. This is what chemistry is called Resonance.
Other scientific areas in which Pauling turned his glorious efforts are quantum chemistry, organic and inorganic chemistry, immunology, metallurgy, anesthesiology, and others. The name of Linus Pauling also enthusiastically recalls that the scientist pays great attention to the innovative idea of the time that is most likely today.
With s p 3 --- - - ---
In the excited state, 4 equivalent hybrid orbitals are formed. The arrangement of bonds corresponds to the direction of the central angles of a regular tetrahedron, the angle between any two bonds is 109 0 28,.
In alkanes and their derivatives (alcohols, halogen-alkanes, amines) all atoms of carbon, oxygen, nitrogen are in the same hybrid sp 3 state. The carbon atom forms four, the nitrogen atom is three, the oxygen atom is two covalent σ -connection. Around these bonds possible free rotation of the parts of the molecule relative to each other.
In the excited state of sp 2, three equivalent hybrid orbitals arise, the electrons located on them form three σ -connections, which are located in the same plane, the angle between the connections 120 0. Non-hybridized 2p - orbitals of two neighboring atoms form π -connection. It is located perpendicular to the plane in which there are σ -connection. The interaction of p-electrons is in this case called "lateral overlapping". A multiple bond does not allow around itself free rotation of parts of the molecule. The fixed position of the parts of the molecule is accompanied by the formation of two geometric planar isomeric forms, which are called: cis (cis) - and trans (trans) - isomers. (cis- lat- on one side, trans lat- through).
π -connection
Atoms bound by a double bond are in a state of hybridization of sp 2 and
present in alkenes, aromatic compounds, form a carbonyl group
\u003e C = O, azomethine group (imino group) -CH = N-
With sp 2 - --- - ---
The structural formula of an organic compound is depicted using Lewis structures (each pair of electrons between atoms is replaced by a dash)
C 2 H 6 CH 3 - CH 3 H H
1.3. Polarization of covalent bonds
Covalent polar bond is characterized by an uneven distribution of electron density. To indicate the direction of the displacement of the electron density using two conventional images.
Polar σ - bond. The electron density shift is indicated by an arrow along the communication line. The end of the arrow is directed towards the more electronegative atom. The appearance of partial positive and negative charges is indicated by the letter "b" "delta" with the desired charge sign.
b + b- b + b + b- b + b-
CH 3 -\u003e O<- Н СН 3 - > C1 CH 3 -\u003e NH 2
methanol chloromethane aminomethane (methylamine)
Polar π -connection. The electron density shift is denoted by a semicircular (curved) arrow above the pi bond, also directed toward the more electronegative atom. ()
b + b- + b-
H 2 C = O CH 3 - C === O
methane |
CH 3 propanone -2
1. Determine the type of hybridization of carbon, oxygen, nitrogen atoms in compounds A, B, B. Name the compounds using the rules of the IUPAC nomenclature.
A. CH 3 -CH 2 - CH 2 -OH B. CH 2 = CH - CH 2 - CH = O
B. CH 3 - N H– C 2 H 5
2. Make the symbols that characterize the direction of polarization of all the indicated bonds in the compounds (A – D)
A. CH 3 - Br B. C 2 H 5 - O-H B. CH 3 -NH- C 2 H 5
G. C 2 H 5 - CH = O
PAILED SYSTEMS
Keywords
MULTIPLE LINKS , chemical two-center bonds, in contrast to simple bonds, are formed by more than one pair of electrons. According to the number of pairs of electrons that make up K. s., There are double, triple, and quadruple bonds. In approximation molecular orbitals of methodsK. p. are compared with mol. orbitals, to-rye on St.-you symmetry is divided into s -, p - and d-orbitals. p-Orbitals are antisymmetric with respect to the plane passing through the bond. AT polyatomic molecules this plane is common to the entire molecule or to a mol. fragment, including this link. d -Orbitals are antisymmetric with respect to two mutually perpendicular planes passing through a bond. With the formation of K. s. As a rule, one (or more) s orbital arises and at least one p or d orbital is necessary. For this reason, the components of K. s. Defined by p - or d-orbitals, called. acc. p - or d -connections. Atoms of intransitive elements in molecules and ions m. B. linked by simple, double and triple bonds. The formation of a simple d -C-C bond in an ethane molecule is correlated with the overlapping of two sp 3 -bigth orbitals of carbon atoms. In the ethylene molecule, in addition to the s -C-C bond, there is one, and in the acetylene molecule with a triple bond, two p-bonds:
The fourth bond (and mb. Bonds of higher multiplicity) is characteristic only for transition metals. d-Opening leads to the formation of quadruple bonds in the salts of the octal halide dihydrogenate anion Re 2 Hal 8 2-, molybdenum and tungsten carboxylates M (OOCR) 4, intracomplex compounds. chromium and vanadium M 2 A 2, where A is 2,6-dimethoxyphenyl. Energetic contributions attributable decomp. types are unequal. Usually, the p-bond energy averages about 80% of the s-bond energy, and the contribution of the d-bond is estimated, for example, in salts of the octachlorodiransnate anion at only 14% of the total binding energy. The higher the multiplicity of the bond, the greater its strength (dissociation energy), the shorter the interatomic distance and the greater the force constant of the bond (see table). 
Two or more K. p. can form in chemical connection of the system of cumulated and conjugated bonds. In the first case, two double bonds are adjacent to the same atom as, for example, in the allele H 2 C = C = CH 2; in the second, double or (and) triple bonds are separated by one simple, as, for example, in 1,3-butadiene H 2 C = CH-CH = CH 2 or acrylonitrile. In conjugate systems, the multiplicity of communication is not m. B. defined by integer. A measure of the multiplicity of a bond (its population by electrons) is a fractional value of the order of the bond, the calculation of which is usually carried out using quantum chemistry methods. Lit .:Gillespie R., Geometry of Molecules, trans. with English, M., 1975; Cotton, F. A., Walton, R., Metal-to-metal multiple bonds, trans. from English, M., 1985. V.I. Minkin.
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