Covalent Bond Definition

A covalent bond is created when the two atoms involved share their electrons equally. The shared pair or bonding pair is the name given to the electron pair in this kind of interaction. Covalent bonds are also known as molecular bonds. The atoms will be able to retain their stability in their outer shell by sharing bonding pairs, just like noble gas atoms do.

What are covalent bonds?

Extremely high ionisation energy elements are unable to transmit electrons, and extremely low electron affinity elements are unable to accept electrons. In order for both atoms to achieve stability by creating an octet configuration in their respective valence shells, the atoms of these elements commonly share their electrons with those of other elements or with other atoms of the same element. Covalent bonds are those associations that involve sharing electron pairs between different or similar sorts of molecules.

Covalent bonding can be found in two Ways:

1. The sharing of electrons amongst similar-type atoms. For instance, H2, Cl2, O2, etc.
2. The transfer of electrons between different types of atoms For example, the production of CH4, H2, NH3, etc.

Atomic covalent bonding in the carbon

According to Carbon's electronic configuration, it must either gain or lose 4 electrons to become stable, which seems impossible given that:

1. Carbon cannot become C4- by gaining 4 electrons because it would be difficult for its 6 protons to hold 10 electrons, which would cause the atom to become unstable.
2. It would be very energy-intensive for carbon to lose 4 electrons in order to form C4+, and the C4+ would only have 2 electrons retained by the proton, making it unstable once more.
3. In order to fulfil its nearest noble gas stage and form a covalent bond, carbon must share one electron because it cannot receive or give away electrons.

Different properties of covalent bond

Several covalent bonds' features are listed below:

1. If a single electron pair shared between them does not fulfil the normal valence of each atom, the atoms may share more than one electron pair.
2. New electrons are not created as a result of covalent bonds. They are only paired through the bond.
3. A covalent bond typically includes the energy of around 80 kilocalories per mole (kcal/mol), making them particularly potent chemical bonds between atoms.
4. After being formed, covalent bonds hardly ever spontaneously break.
5. Covalent bonds are directional, with the bonded atoms displaying certain orientations with respect to one another.
6. Most covalently linked substances have relatively low melting and boiling temperatures, and they frequently have lower vaporisation and fusion enthalpies.
7. The absence of free electrons in compounds created by covalent bonding prevents them from conducting electricity.
8. Covalent substances are not water soluble.

What is Octet Rule?

Except for noble gases, all atoms have less than eight electrons in their valence shell. In other words, the valence shells of these atoms are devoid of stable structures. They consequently combine to create stable electronic structures, either in conjunction with other atoms or with one another.

Because of this, "Chemical combination is caused by the inclination of atoms of diverse elements to acquire stable configuration of eight electrons in their valence shells," and "The principle of achieving the maximum of eight electrons in the valence shell of atoms is known as the octet rule,". Lewis devised straightforward symbols to represent the valence electrons, which make up an atom's outermost shell. These symbols are known as electron dot symbols, and the chemical's structure is known as the Lewis Dot Structure.

Conditions for writing the Lewis dot structures

Covalent bonds are created when two atoms are combined and share an electron pair, and each bond is made up of two electrons that are provided by each combining atom. By exchanging electrons, each atom creates an octet configuration in its valence shell.

Covalent compounds' electron dot structures are expressed according to the octet rule. According to this rule, every atom in the molecule has eight electrons in its valence shell, with the exception of the hydrogen atom. Since just two electrons are required for hydrogen to reach the helium form, it will only have two electrons.

Group 17 elements such as Cl would share one electron, group 16 elements such as O and S would share two electrons, group 15 elements would share three electrons, and so on in order to form a stable octet. The oxygen atom, which has six electrons in its valence shell, completes its octet by exchanging its two electrons with two hydrogen atoms to form the water molecule.

Different types of covalent bonds

Depending upon the different numbers of shared electron pairs, the covalent bond can be classified into:

• Single Covalent Bond
• Double Covalent Bond
• Triple Covalent Bond

Single bonds

A solitary bond is produced when the two involved atoms share just one pair of electrons. It is represented by one dash (-). This type of covalent connection is the most stable even though it is weaker than double and triple bonds and has a lower density.

For example, the HCl molecule is composed of one Hydrogen atom with one valence electron and one Chlorine atom with seven valence electrons. In this instance, hydrogen and chlorine share one electron to create a single bond.

Double bonds

A double bond is produced when two pairs of electrons are shared by the two involved atoms. Its identifier is two dashes (=). Double covalent bonds are significantly more strong than single ones despite being less stable.

Example: The carbon dioxide molecule is composed of two oxygen atoms with four valence electrons and one carbon atom with six valence electrons.

To complete its octet, carbon shares two of its valence electrons with one oxygen atom and two with a second oxygen atom. Because each oxygen atom shares its two electrons with carbon, CO₂ has two double bonds.

The oxygen molecule is created when six electrons are present in the valence shell of each oxygen atom. Two more electrons are required to complete the octet of each atom. The sharing of two electrons between the atoms results in the formation of the oxygen molecule. Due to the sharing of two electron pairs, there is a double bond between the two oxygen atoms.

Two of the valence electrons of each carbon atom in the ethylene molecule are shared with two hydrogen atoms, while the remaining two electrons are shared with the other carbon atom. As a result, the carbon atoms form a double bond.

Triple bond

A triple bond is produced when the two involved atoms share three pairs of electrons. Triple covalent bonds, which are indicated by three dashes, are the least stable covalent bonds.

For illustration: During the synthesis of a nitrogen molecule, each nitrogen atom, which has five valence electrons, donates three electrons to form three electron pairs. The two nitrogen atoms are thereby joined by a triple bond.

Polar covalent bond

When two atoms are joined, a type of covalent bond results from the unequal sharing of electrons caused by the atoms' differing electronegativities. More electronegative atoms will more strongly attract electrons. There is an electronegative difference between the atoms that is greater than 0 but less than 2.0. As a result, the common pair of electrons will be closer to that atom. Consider molecules that hydrogen bond as an example due to an unbalanced electrostatic potential. Here, the electronegative fluorine, hydrogen, or oxygen interacts with the hydrogen atom.

Nonpolar covalent bond

This type of covalent connection develops when the electrons are distributed equally among the atoms. The electronegativity of the two atoms is same. It occurs whenever the joining atoms have similar electron affinities (diatomic elements). For instance, gas molecules with nonpolar covalent bonds include hydrogen gas, nitrogen gas, etc.

Polarization of covalent bonds

It has been observed that the more electronegative of the two atoms is always closer to the electron cloud in sigma bonds produced by two different atoms. Because a permanent dipole develops as a result, the covalent bond is known as being polarised.

The covalent bonds in a water molecule's polarity are depicted in the diagram above. The more electronegative atom in a polar covalent bond is said to have a partial negative charge, whereas the less electronegative atom has a partial positive charge.

Difference between covalent and ionic bonds

Atomic bonds can have an ionic or covalent structure. These relationships have a variety of topologies and traits. Pairs of electrons are included in covalent bonds through the joining of two atoms in a specific configuration. Ionic bonds, on the other hand, are connections that connect two ions.

When two non-metallic atoms are in a covalent link, their electron pairs are shared, and there are other covalent bonds with electronegativity differences more than 2.0 (>2.0). Polyatomic ions are created when covalent bonds are established. While the electrostatic attraction between the oppositely charged ions creates the ionic connection.