CONCEPTS

What is a covalent bond?

We explain what a covalent bond is and some of its characteristics. In addition, covalent bond types and examples.

  1. What is a covalent bond?

It is called covalent bond to a type of chemical bond , which occurs when two atoms bond to form a molecule, sharing electrons belonging to its most superficial layer, thereby reaching the known “stable octet” (according to the “octet rule ”Proposed by Gilbert Newton Lewis on the electrical stability of atoms). The atoms thus linked share a pair (or more) of  electrons , whose orbit varies and is called the  molecular orbital.

Covalent bonds are different from ionic bonds , in which an electron transfer occurs and occurs between metallic elements. The latter also form electrically charged molecules, called ions: cations if they have a positive charge, anions if they have a negative charge.

In contrast, certain covalent bonds (between different atoms) are characterized by a concentration of electronegativity in one of the two atoms together, since they do not attract the cloud of electrons around them with the same intensity.
This results in an electric dipole, that is, a molecule with a positive and negative charge at its ends, such as an ordinary battery: a positive pole and a negative pole. Thanks to this,  covalent molecules join with similar ones and form more complex structures.

  1. Types of covalent bond

covalent bond
In a double bond the bound atoms contribute two electrons each.

There are the following types of covalent bond, based on the amount of electrons shared by the bonded atoms:

  • Simple . The bound atoms share a pair of electrons from their last layer (one electron each). For example: HH (Hydrogen-Hydrogen), H-Cl (Hydrogen-Chlorine).
  • Double . The bound atoms provide two electrons each, forming a bond of two pairs of electrons. For example: O = O (Oxygen-Oxygen), O = C = O (Oxygen-Carbon-Oxygen).
  • Triple . In this case the bound atoms provide three pairs of electrons, that is, six in total. For example: N≡N (Nitrogen-Nitrogen).
  • Dative . A type of covalent bond in which only one of the two atoms linked provides two electrons and the other, however, none.

On the other hand, according to the presence or not of polarity, one can distinguish between polar covalent bonds (which form polar molecules) and non-polar covalent bonds (which form non-polar molecules):

  • Covalent polar bonds . Atoms of different elements are linked and with electronegativity difference above 0.5. Thus electromagnetic dipoles are formed.
  • Non-polar covalent bonds . Atoms of the same element or identical polarities are linked, with a very small electronegativity difference (less than 0.4). The electronic cloud is thus attracted with equal intensity by both nuclei and a molecular dipole is not formed.
  1. Examples of covalent bonding

Covalent bond
Pure nitrogen (N2) has a triple bond.

Simple examples of covalent bonding are those given in the following molecules:

  • Or pure  oxygen  (O ) . O = O (a double bond)
  • pure  idrogen  (H ) . HH (a simple link)
  • ioxido carbon (CO ) . O = C = O (two double bonds)
  • gua (H O) . HOH (two simple links)
  • A acid hydrochloric ( HCl ) . H-Cl (a simple link)
  • itrogeno  pure  (N2) . N≡N (a triple bond)
  • A acid hydrocyanic (HCN) . HC≡N (a single link and a triple link)

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