Far from the last role at the chemical level of the organization of the world is played by the method of connection of structural particles, interconnection. The vast majority of simple substances, namely non-metals, have a covalent non-polar type of bond, with the exception of inert gases. Pure metals have a special way of bonding, which is realized through the socialization of free electrons in the crystal lattice.
All complex substances (except some organic ones) have covalent polar chemical bonds. The types and examples of these compounds will be discussed below. In the meantime, it is necessary to find out which characteristic of the atom affects the polarization of the bond.
Electronegativity
Atoms, or rather their nuclei (which, as we know, are positively charged), have the ability to attract and hold electron density, in particular, when forming a chemical bond. This property was called electronegativity. In the periodic table, its value grows in periods and main subgroups of elements. The value of electronegativity is not always constant and can change, for example, when changing the type of hybridization thatatomic orbitals.
Chemical bonds, the types and examples of which will be indicated below, or rather, the localization or partial displacement of these bonds to one of the binding participants, is explained precisely by the electronegative characteristic of one or another element. The shift occurs to the atom for which it is stronger.
Covalent non-polar bond
The "formula" of a covalent non-polar bond is simple - two atoms of the same nature unite the electrons of their valence shells into a joint pair. Such a pair is called shared because it equally belongs to both participants in the binding. It is thanks to the socialization of the electron density in the form of a pair of electrons that the atoms pass into a more stable state, as they complete their external electronic level, and the “octet” (or “doublet” in the case of a simple hydrogen substance H2, it has a single s-orbital, which requires two electrons to complete) is the state of the outer level to which all atoms aspire, since its filling corresponds to the state with the minimum energy.
An example of a non-polar covalent bond exists in the inorganic and, no matter how strange it may sound, but also in organic chemistry. This type of bond is inherent in all simple substances - non-metals, except for noble gases, since the valence level of an inert gas atom is already completed and has an octet of electrons, which means that bonding with a similar one does not make sense for it and is even less energetically beneficial. In organics, non-polarity occurs in individual moleculesa certain structure and is conditional.
Covalent polar bond
An example of a non-polar covalent bond is limited to a few molecules of a simple substance, while dipole compounds in which the electron density is partially shifted towards a more electronegative element are the vast majority. Any combination of atoms with different electronegativity values gives a polar bond. In particular, bonds in organics are covalent polar bonds. Sometimes ionic, inorganic oxides are also polar, and in s alts and acids, the ionic type of binding predominates.
As an extreme case of polar binding, the ionic type of compounds is sometimes considered. If the electronegativity of one of the elements is significantly higher than that of the other, the electron pair is completely shifted from the bond center to it. This is how the separation into ions occurs. The one who takes an electron pair turns into an anion and gets a negative charge, and the one who loses an electron turns into a cation and becomes positive.
Examples of inorganic substances with a covalent non-polar bond type
Substances with a covalent non-polar bond are, for example, all binary gas molecules: hydrogen (H - H), oxygen (O=O), nitrogen (in its molecule 2 atoms are connected by a triple bond (N ≡ N)); liquids and solids: chlorine (Cl - Cl), fluorine (F - F), bromine (Br - Br), iodine (I - I). As well as complex substances consisting of atoms of different elements, but with the actual sameelectronegativity value, for example, phosphorus hydride - pH3.
Organics and non-polar binding
It is clear that all organic matter is complex. The question arises, how can there be a non-polar bond in a complex substance? The answer is quite simple if you think a little logically. If the electronegativity values of the coupled elements differ insignificantly and do not create a dipole moment in the compound, such a bond can be considered nonpolar. This is exactly the situation with carbon and hydrogen: all C-H bonds in organics are considered non-polar.
An example of a nonpolar covalent bond is a molecule of methane, the simplest organic compound. It consists of one carbon atom, which, according to its valency, is connected by single bonds with four hydrogen atoms. In fact, the molecule is not a dipole, since there is no localization of charges in it, to some extent due to the tetrahedral structure. The electron density is evenly distributed.
An example of a non-polar covalent bond exists in more complex organic compounds. It is realized due to mesomeric effects, i.e. sequential pulling of the electron density, which quickly fades along the carbon chain. So, in the hexachloroethane molecule, the C-C bond is non-polar due to the uniform pulling of the electron density by six chlorine atoms.
Other types of links
In addition to the covalent bond, which, by the way, can also be carried out according to the donor-acceptor mechanism, there are ionic, metallic andhydrogen bonds. Brief characteristics of the penultimate two are presented above.
Hydrogen bond is an intermolecular electrostatic interaction that is observed if the molecule has a hydrogen atom and any other atom that has unshared electron pairs. This type of bonding is much weaker than the others, but due to the fact that a lot of these bonds can form in the substance, it makes a significant contribution to the properties of the compound.
