Adjective covalent It is used in the field of chemistry to qualify the bond that is generated between atoms that have shared electron pairs. It is also classified as covalent that which has at least one covalent bond.
It is important to remember that the particles that have an electrical charge and are made up of a molecule or an atom that is not neutral are called ions. The ions, according to the octet rule what the american enunciated Gilbert Newton Lewis on 1916, have a tendency to use Eight electrons to complete the last energy levels and thus achieve stability in your configuration.
The atoms, to respect the octet rule, they can appeal to different classes of chemical links to join. Among them appears the covalent bond, what does the electron sharing at the last level. This type of bond requires that the electronegativity difference between the atoms is less than 1.7.
Covalent bonds develop between atoms of different elements not metals and between atoms that belong to the same nonmetal element. Covalently bonded atoms share their pairs of electrons in the molecular orbital.
These atoms can share between one and three pairs of electrons in a covalent bond: therefore the bonds can be simple, double or triples depending on the case. If the bond occurs between equal atoms that have an electronegativity difference less than 0.4, you get a apolar covalent bond. On the other hand, if the bond is developed by atoms of different elements that have an electronegativity difference greater than 0.4, It’s about a polar covalent bond.
According to the chemists G. William Daub and S. Seese, in any covalent substance (such as a molecule of hydrogen) the following four aspects are appreciated:
* If observed individually, that is to say outside of a combination, atoms have properties that are very different from those exhibited by molecules. For this reason, when writing the chemical formula of hydrogen, for example, we must put a two as a subscript of the H, since it is a diatomic molecule (one that is made up of two atoms, whether or not they are of the same chemical element);
* the two electrons are attracted to the two positive nuclei, something that happens in order to produce a more stable molecule than one in which the atoms are separated. This causes a covalent bond to be generated. Given that the attraction to which the nuclei submit to the electrons manages to cancel the repulsion between them, there is a good chance of finding electrons between the two nuclei;
* the distance between the nuclei has to allow the 1s orbitals to have the maximum overlap. For example, this value in the hydrogen molecule is around 0.74 angstrom. If this is not fulfilled, then it is spoken of link length to define the distance what is between two covalently bonded atoms;
* It takes 52 kilocalories to cut the covalent bonds that exist in 1 gram of hydrogen gas.
With regard to covalent substances, it is possible to recognize the following two:
* the molecular covalents, that is to say, the bonds that form molecules with low boiling and melting temperatures, insulating from heat and electric current, soluble in polar or apolar solvents (depending on whether they are polar or apolar). molecules), such as benzene, nitrogen, oxygen and carbon;
* the lattice covalent, crystalline networks with an undefined number of atoms, similar to ionic compounds, characterized by being very hard, insoluble and with high boiling and melting temperatures, such as diamond and quartz.