Not the least role at the chemical level of the organization of the world is played by the method of connecting structural particles, compounds among themselves. 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 in their pure form have a special bonding method, 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. Types and examples of these compounds will be discussed below. In the meantime, it is necessary to find out what 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 retain electron density, in particular, during the formation of a chemical bond. This property has been 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, with a change in the type of hybridization into which atomic orbitals enter .
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 this or that element. The shift occurs to the atom in which it is stronger.
Covalent non-polar bond
The “formula” of the covalent non-polar bond is simple - two atoms of the same nature combine the electrons of their valence shells into a joint pair. Such a pair is called divided because it belongs equally to both participants in the binding. It is due to the socialization of the electron density in the form of a pair of electrons that the atoms transfer to a more stable state, since they complete their external electronic level, and the “octet” (or “doublet” in the case of a simple substance of hydrogen is H 2 , it has a single s-orbital, for completion of which two electrons are needed) is the state of the external level, to which all atoms tend, since its filling corresponds to a state with minimum energy.
An example of a nonpolar covalent bond is in an 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 linking with a similar one does not make sense to it and is even less energetically beneficial. In organic matter, non-polarity is found in individual molecules of a certain structure and is conditional.
Covalent polar bond
An example of a nonpolar covalent bond is limited to a few molecules of a simple substance, while dipole compounds in which the electron density is partially biased towards a more electronegative element are the vast majority. Any combination of atoms with different electronegativity gives a polar bond. In particular, bonds in organics are covalent polar bonds. Sometimes ionic, inorganic oxides are also polar, and in the salts and acids the ionic type of binding prevails.
As an extreme case of polar binding, the ionic type of compounds is sometimes also considered. If the electronegativity of one of the elements is much higher than that of the other, the electron pair is completely shifted from the center of communication to it. This is the division into ions. The one who takes the electron pair turns into an anion and receives a negative charge, and the losing electron turns into a cation and becomes positive.
Examples of inorganic substances with a covalent non-polar type of bond
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 various elements, but with the actual identical value of electronegativity, for example, phosphorus hydride - PH 3 .
Organics and nonpolar binding
It is extremely clear that all organic substances are complex. The question is, how can a non-polar bond be in a complex substance? The answer is quite simple, if you think a little logically. If the values of the electronegativity of the coupled elements differ slightly and do not create a dipole moment in the compound, such a connection can be considered nonpolar. This is precisely the situation with carbon and hydrogen: all C - H bonds in the organic matter are considered nonpolar.
An example of a nonpolar covalent bond is a methane molecule, 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, in some way due to the tetrahedral structure. The electron density is distributed evenly.
An example of nonpolar covalent bond is also found in more complex organic compounds. It is realized due to mesomeric effects, that is, sequential delaying of electron density, which quickly fades away along the carbon chain. So, in the hexachloroethane molecule, the C - C bond is nonpolar due to the uniform pulling of the electron density by six chlorine atoms.
Other types of relationships
In addition to the covalent bond, which, by the way, can also be carried out by the donor-acceptor mechanism, there are ionic, metal, and hydrogen bonds. Brief characteristics of the penultimate two are presented above.
A hydrogen bond is an intermolecular electrostatic interaction that occurs if a molecule has a hydrogen atom or any other atom that has lone electron pairs. This type of binding is much weaker than the others, but due to the fact that a lot of these bonds can form in a substance, it makes a significant contribution to the properties of the compound.