Covalent bond - this is a bond between two atoms due to the formation of a common electronic pair.
Covalent non-polar bond– this bond between atoms with equal
electronegativity.For example: Н 2, О 2, N 2, Cl 2, etc. The dipole moment of such bonds is equal to zero.
Covalent polar bond – this bond between atoms with different electronegativity.The overlapping zone of electron clouds is shifted towards a more electronegative atom.
For example, H – Cl (H b + → Cl b–).
A covalent bond has the following properties:
- saturation - the ability of an atom to form a number of chemical bonds corresponding to its valence;
- directivity - the overlap of electron clouds occurs in the direction providing the maximum overlap density.
Ionic bond– it is a bond between oppositely charged ions. It can be viewed as an extreme case of covalent polar connection... Such a connection arises when there is a large difference in the electronegativities of atoms,
forming a chemical bond. For example, in the NaF molecule, the difference
electronegativities is 4.0 – 0.93 \u003d 3.07, which leads to an almost complete transition of an electron from sodium to fluorine:
The interaction of ions of opposite sign does not depend on the direction, and the Coulomb forces do not possess the property of saturation. Because of this, the ionic bond does not have directionality and saturation.
Metal bond– this is the connection of positively charged metal ions with free electrons.
Most metals have a number of properties that are general in nature and differ from those of other substances. Such properties are relatively high melting points, ability to reflect light, high thermal and electrical conductivity. This is a consequence of the formation between metal atoms of a special type of bond - a metal bond.
In metal atoms, valence electrons are weakly bound to their nuclei and can easily be detached from them. As a result, in crystal lattice metal, positively charged metal ions and "free" electrons appear, the electrostatic interaction of which provides a chemical bond.
Hydrogen bond– it is a bond through a hydrogen atom bonded to a highly electronegative element.
A hydrogen atom bound to a highly electronegative element (fluorine, oxygen, nitrogen, etc.) gives up almost completely an electron from the valence orbital. The resulting free orbital can interact with the lone pair of electrons of another electronegative atom, resulting in a hydrogen bond. By the example of water and acetic acid molecules, the hydrogen bond is shown by dashed lines:
This bond is much weaker than other chemical bonds (the energy of its formation is 10–40 kJ / mol). Hydrogen bonds can occur both between different molecules and within a molecule.
Hydrogen bonds play an extremely important role in such inorganic substances as water, hydrofluoric acid, ammonia, etc., as well as in biological macromolecules.
Basic types chemical bond
main types of chemical bonds.
You know that atoms can combine with each other to form both simple and complex substances. In this case, various types of chemical bonds are formed: ionic, covalent (non-polar and polar), metallic and hydrogen. One of the most essential properties of atoms of elements that determine which bond is formed between them - ionic or covalent - it is electronegativity, i.e. the ability of atoms in a compound to attract electrons to themselves.
A conditional quantitative assessment of electronegativity is given by the scale of relative electronegativity.
In periods, there is a general tendency towards an increase in the electronegativity of elements, and in groups - their fall. Elements by electronegativity are arranged in a row, on the basis of which the electronegativities of elements in different periods can be compared.
The type of chemical bond depends on how large the difference in the values \u200b\u200bof the electronegativities of the connecting atoms of elements is. The more the atoms of the elements forming the bond differ in electronegativity, the more polar the chemical bond is. It is impossible to draw a sharp line between the types of chemical bonds. In most compounds, the type of chemical bond is intermediate; for example, a highly polar covalent chemical bond is close to an ionic bond. Depending on which of the limiting cases the chemical bond is closer in nature to, it is referred to either an ionic or a covalent polar bond.
Ionic bond.
An ionic bond is formed by the interaction of atoms, which differ sharply from each other in electronegativity.For example, typical metals lithium (Li), sodium (Na), potassium (K), calcium (Ca), strontium (Sr), barium (Ba) form an ionic bond with typical non-metals, mainly halogens.
In addition to alkali metal halides, ionic bonds are also formed in compounds such as alkalis and salts. For example, in sodium hydroxide (NaOH) and sodium sulfate (Na 2 SO 4) ionic bonds exist only between sodium and oxygen atoms (other bonds are covalent polar).
Covalent non-polar bond.
When atoms with the same electronegativity interact, molecules with a covalent non-polar bond are formed.Such a bond exists in the molecules of the following simple substances: H 2, F 2, Cl 2, O 2, N 2. The chemical bonds in these gases are formed by common electron pairs, i.e. when the corresponding electron clouds overlap, due to the electron-nuclear interaction, which is carried out when atoms approach.
When composing electronic formulas of substances, it should be remembered that each common electron pair is a conditional image of increased electron density resulting from the overlap of the corresponding electron clouds.
Covalent polar bond.
During the interaction of atoms, the values \u200b\u200bof the electroretequencies of which differ, but not sharply, a shift of the common electron pair occurs to a more electronegative atom. This is the most common type of chemical bond that occurs in both inorganic and organic compounds.
The covalent bonds fully include those bonds that are formed by the donor-acceptor mechanism, for example, in the ions of hydronium and ammonium.
Metallic bond.
The bond that is formed as a result of the interaction of relatively free electrons with metal ions is called a metal bond.This type of bond is typical for simple substances - metals.
The essence of the process of forming a metal bond is as follows: metal atoms easily donate valence electrons and turn into positive charged ions. Relatively free electrons, detached from the atom, move between positive metal ions. A metallic bond arises between them, that is, the electrons seem to cement the positive ions of the crystal lattice of metals.
Hydrogen bond.
A bond that forms between the hydrogen atoms of one molecule and an atom of a strongly electronegative element(O, N, F) another molecule is called a hydrogen bond.
The question may arise: why exactly hydrogen forms such a specific chemical bond?
This is due to the fact that the atomic radius of hydrogen is very small. In addition, when displacing or completely giving up its only electron, hydrogen acquires a relatively high positive charge, due to which the hydrogen of one molecule interacts with the atoms of electronegative elements that have a partial negative charge that goes into the composition of other molecules (HF, H2O, NH3) ...
Let's look at some examples. We usually depict the composition of water with the chemical formula H 2 O. However, this is not entirely accurate. It would be more correct to denote the composition of water by the formula (H 2 O) n, where n \u003d 2,3,4, etc. This is explained by the fact that individual water molecules are linked through hydrogen bonds.
The hydrogen bond is usually denoted by dots. It is much weaker than ionic or covalent bonds, but stronger than normal intermolecular interactions.
The presence of hydrogen bonds explains the increase in water volume with decreasing temperature. This is due to the fact that as the temperature decreases, the molecules become stronger and therefore the density of their "packing" decreases.
When studying organic chemistry, the following question arose: why are the boiling points of alcohols much higher than the corresponding hydrocarbons? This is explained by the fact that hydrogen bonds are also formed between alcohol molecules.
An increase in the boiling point of alcohols also occurs due to the enlargement of their molecules.
The hydrogen bond is also typical for many other organic compounds (phenols, carboxylic acids, etc.). From courses in organic chemistry and general biology, you know that the presence of a hydrogen bond explains the secondary structure of proteins, the structure of the double helix of DNA, that is, the phenomenon of complementarity.
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The chemical bond arises due to the interaction of electric fields created by electrons and atomic nuclei, i.e. the chemical bond is electrical in nature.
Under chemical bond understand the result of the interaction of 2 or more atoms leading to the formation of a stable polyatomic system. A condition for the formation of a chemical bond is a decrease in the energy of interacting atoms, i.e. the molecular state of matter is energetically more favorable than the atomic state. When a chemical bond is formed, atoms tend to obtain a complete electron shell.
Distinguish: covalent, ionic, metallic, hydrogen and intermolecular.
Covalent bond - the most general form chemical bond arising from the socialization of an electron pair through exchange mechanism -, when each of the interacting atoms supplies one electron, or donor-acceptor mechanismif an electron pair is transferred for general use by one atom (donor - N, O, Cl, F) to another atom (acceptor - atoms of d-elements).
Chemical bond characteristics.
1 - multiplicity of bonds - only 1 sigma bond is possible between 2 atoms, but along with it there can be pi and delta bonds between the same atoms, which leads to the formation of multiple bonds. The multiplicity is determined by the number of common electron pairs.
2 - bond length - internuclear distance in a molecule, the greater the multiplicity, the shorter its length.
3 - bond strength is the amount of energy required to break it
4 - the saturation of the covalent bond is manifested in the fact that one atomic orbital can take part in the formation of only one c.s. This property determines the stoichiometry of molecular compounds.
5 - directionality of c.s. depending on the shape and direction of the electron clouds in space, when they overlap, compounds with the linear and angular shape of molecules can be formed.
Ionic bond – formed between atoms that are very different in electronegativity. These are compounds of the main subgroups 1 and 2 of groups with elements of the main subgroups of 6 and 7 groups. Ionic is a chemical bond that occurs as a result of mutual electrostatic attraction of oppositely charged ions.
The mechanism of the formation of ionic bonds: a) the formation of ions of interacting atoms; b) the formation of a molecule due to the attraction of ions.
Non-directionality and unsaturation of the ionic bond
The force fields of the ions are evenly distributed in all directions, so each ion can attract ions of the opposite sign to itself in any direction. This is the non-directionality of the ionic bond. The interaction of 2x ions of opposite sign does not lead to a complete mutual compensation of their force fields. Therefore, they retain the ability to attract ions in other directions, i.e. the ionic bond is characterized by unsaturation. Therefore, each ion in an ionic compound attracts such a number of ions of the opposite sign to form a crystal lattice of the ionic type. There are no molecules in an ionic crystal. Each ion is surrounded by a certain number of ions of a different sign (ion coordination number).
Metal bond - chem. Bonding in metals. Metals have an excess of valence orbitals and a lack of electrons. When atoms approach each other, their valence orbitals overlap, due to which electrons move freely from one orbital to another, and a bond is established between all metal atoms. The bond that is carried out by relatively free electrons between metal ions in the crystal lattice is called a metal bond. The bond is highly delocalized and lacks directionality and saturation, because valence electrons are evenly distributed throughout the crystal. The presence of free electrons determines the existence general properties metals: opacity, metallic luster, high electrical and thermal conductivity, malleability and ductility.
Hydrogen bond - the bond between the H atom and a strongly negative element (F, Cl, N, O, S). Hydrogen bonds can be intra- and intermolecular. BC is weaker than the covalent bond. The emergence of the sun is explained by the action of electrostatic forces. The H atom has a small radius and upon displacement or recoil of a single electron H acquires a strong positive charge, which acts on electronegativity.
The main types of chemical bonds.
You know that atoms can combine with each other to form both simple and complex substances... In this case, various types of chemical bonds are formed: ionic, covalent (non-polar and polar), metallic and hydrogen. One of the most essential properties of atoms of elements that determine which bond is formed between them - ionic or covalent - it is electronegativity, i.e. the ability of atoms in a compound to attract electrons to themselves.
A conditional quantitative assessment of electronegativity is given by the scale of relative electronegativity.
In periods, there is a general tendency towards an increase in the electronegativity of elements, and in groups - their fall. Elements by electronegativity are arranged in a row, on the basis of which the electronegativities of elements in different periods can be compared.
The type of chemical bond depends on how large the difference in the values \u200b\u200bof the electronegativities of the connecting atoms of elements is. The more the atoms of the elements forming the bond differ in electronegativity, the more polar the chemical bond is. It is impossible to draw a sharp line between the types of chemical bonds. In most compounds, the type of chemical bond is intermediate; for example, a highly polar covalent chemical bond is close to an ionic bond. Depending on which of the limiting cases the chemical bond is closer in nature to, it is referred to either an ionic or a covalent polar bond.
Ionic bond.
An ionic bond is formed by the interaction of atoms, which differ sharply from each other in electronegativity.For example, typical metals lithium (Li), sodium (Na), potassium (K), calcium (Ca), strontium (Sr), barium (Ba) form an ionic bond with typical non-metals, mainly halogens.
In addition to alkali metal halides, ionic bonds are also formed in compounds such as alkalis and salts. For example, sodium hydroxide (NaOH) and sodium sulfate (Na 2 SO 4 ) ionic bonds exist only between sodium and oxygen atoms (other bonds are covalent polar).
Covalent non-polar bond.
When atoms with the same electronegativity interact, molecules with a covalent non-polar bond are formed.Such a bond exists in the molecules of the following simple substances: H 2, F 2, Cl 2, O 2, N 2 ... The chemical bonds in these gases are formed by common electron pairs, i.e. when the corresponding electron clouds overlap, due to the electron-nuclear interaction, which is carried out when atoms approach.
When composing electronic formulas of substances, it should be remembered that each common electron pair is a conditional image of increased electron density resulting from the overlap of the corresponding electron clouds.
Covalent polar bond.
During the interaction of atoms, the values \u200b\u200bof the electroretequencies of which differ, but not sharply, a shift of the common electron pair occurs to a more electronegative atom. This is the most common type of chemical bond that occurs in both inorganic and organic compounds.
The covalent bonds fully include those bonds that are formed by the donor-acceptor mechanism, for example, in the ions of hydronium and ammonium.
Metallic bond.
The bond that is formed as a result of the interaction of relatively free electrons with metal ions is called a metal bond.This type of bond is typical for simple substances - metals.
The essence of the metal bond formation process is as follows: metal atoms easily donate valence electrons and turn into positive charged ions. Relatively free electrons, detached from the atom, move between positive metal ions. A metallic bond arises between them, that is, the electrons seem to cement the positive ions of the crystal lattice of metals.
Hydrogen bond.
A bond that forms between the hydrogen atoms of one molecule and an atom of a strongly electronegative element(O, N, F) another molecule is called a hydrogen bond.
The question may arise: why exactly hydrogen forms such a specific chemical bond?
This is explained by atomic radius hydrogen is very small. In addition, when displacing or giving up its only electron, hydrogen acquires a relatively high positive charge, due to which the hydrogen of one molecule interacts with the atoms of electronegative elements that have a partial negative charge that goes into the composition of other molecules (HF, H2O, NH3 ).
Let's look at some examples. We usually depict the composition of water chemical formula H2
O. However, this is not entirely accurate. It would be more correct to denote the composition of water by the formula (H2
O) n, where n \u003d 2,3,4, and so on. This is due to the fact that individual water molecules are linked through hydrogen bonds.
The hydrogen bond is usually denoted by dots. It is much weaker than ionic or covalent bondbut stronger than the usual intermolecular interaction.
The presence of hydrogen bonds explains the increase in water volume with decreasing temperature. This is due to the fact that as the temperature decreases, the molecules become stronger and therefore the density of their "packing" decreases.
When studying organic chemistry the following question arose: why are the boiling points of alcohols much higher than the corresponding hydrocarbons? This is explained by the fact that hydrogen bonds are also formed between alcohol molecules.
An increase in the boiling point of alcohols also occurs due to the enlargement of their molecules.
The hydrogen bond is typical for many others. organic compounds (phenols, carboxylic acids, etc.). You know from organic chemistry and general biology courses that the presence of hydrogen bond explains the secondary structure of proteins, the structure of the double helix of DNA, that is, the phenomenon of complementarity.