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Covalent Bond – Definition, Types, Properties, Examples

  • Last Updated : 10 Nov, 2021

A covalent bond is formed when electrons from both participating atoms are shared equally. The pair of electrons involved in this type of bonding is known as a shared pair or bonding pair. Molecular bonds are another name for covalent bonds. The sharing of bonding pairs will ensure that the atoms achieve stability in their outer shell, similar to noble gas atoms.

Elements with extremely high ionization energies are incapable of transferring electrons, and elements with extremely low electron affinity are incapable of absorbing electrons. The atoms of such elements tend to share electrons with atoms of other elements or atoms of the same element in such a way that both atoms achieve octet configuration in their respective valence shells and thus achieve stability. A covalent Bond refers to such an association formed by the sharing of electron pairs among different or similar kinds.

Properties of Covalent Bond

If sharing a single electron pair between atoms does not satisfy an atom’s normal valence, the atoms may share more than one electron pair between them. Covalent bonds have the following properties:

  • The formation of new electrons is not the result of covalent bonding. The bond only connects them.
  • They are extremely strong chemical bonds that exist between atoms.
  • Covalent bonds rarely break on their own after they are formed.
  • Covalent bonds are directional in the sense that the atoms that are bonded have distinct orientations relative to one another.
  • Most covalently bound compounds to have relatively low melting and boiling points.
  • Compounds with covalent bonds usually have lower enthalpies of vaporization and fusion.
  • Compounds formed by covalent bonding don’t conduct electricity due to the lack of free electrons.
  • Covalent compounds are not soluble in water.

Octet Rule

Except for noble gases, all atoms have fewer than eight electrons in their valence shell. In other words, these atoms’ valence shells do not have stable configurations. As a result, they combine with one another or with other atoms to form stable electronic configurations.

The tendency of atoms of different elements to achieve a stable configuration of eight electrons in their valence shells is the cause of chemical combination, and the principle of achieving a maximum of eight electrons in an atom’s valence shell is known as the octet rule.

Types of Covalent Bonds

Depending upon the number of shared electron pairs, the covalent bond can be classified into Single Double and Triple Covalent Bond.

Single Bonds

When only one pair of electrons is shared by the two participating atoms, a single bond is formed. It is denoted by a single dash (-). Despite having a lower density and being weaker than a double or triple bond, this type of covalent bond is the most stable. 

For example, an HCl molecule contains one Hydrogen atom with one valence electron and one Chlorine atom with seven valence electrons. In this case, hydrogen and chlorine form a single bond by sharing one electron.

Double Bonds

When two pairs of electrons are shared by two participating atoms, a double bond is formed. It’s denoted by two dashes (=). Although double covalent bonds are much stronger than single bonds, they are also less stable.

One carbon atom has six valence electrons and two oxygen atoms have four valence electrons in a carbon dioxide molecule, for example. Carbon shares two of its valence electrons with one oxygen atom and two with another oxygen atom to complete its octet. Because each oxygen atom shares two electrons with carbon, CO2 contains two double bonds.

Oxygen-Molecule: Each oxygen atom in the formation of the oxygen molecule has six electrons in its valence shell. To complete their octet, each atom requires two more electrons. As a result, the atoms share two electrons to form the oxygen molecule. Because two electron pairs are shared, the two oxygen atoms form a double bond.



Triple Bond

When three pairs of electrons are shared by two participating atoms, a triple bond is formed. Triple covalent bonds are the least stable type of covalent bond and are represented by three dashes. 

In the formation of a nitrogen molecule, for example, each nitrogen atom with five valence electrons contributes three electrons to form three electron pairs for sharing. As a result, a triple bond forms between the two nitrogen atoms.

Polar Covalent Bond

This type of covalent bond exists when the electronegativity of combining atoms differs, resulting in unequal electron sharing. Electrons will be drawn to more electronegative atoms. The atoms’ electronegative difference is greater than zero but less than 2. 

As a result, the shared electron pair will be closer to that atom. As an example, consider molecules that form hydrogen bonds as a result of an unbalanced electrostatic potential. The hydrogen atom in this case interacts with electronegative fluorine, hydrogen, or oxygen.

Nonpolar Covalent Bond

This type of covalent bond is formed when two atoms share an equal number of electrons. The difference in electronegativity between two atoms is zero. 

It occurs whenever the atoms combining have a similar electron affinity. Nonpolar Covalent Bonds, for example, can be found in gas molecules such as hydrogen gas, nitrogen gas, and so on.

Comparison between Ionic Bond and Covalent Bond

Covalent Bond

Ionic Bond

A covalent bond is formed when two similar electronegative nonmetals come together.This type of bond is formed when a metal and a non-metal combine.
Bonds formed by covalent bonding have a distinct shape.No definite shape
Low melting and boiling pointHigh melting and boiling point
low polarityHigh Polarity
More flammableLess flammable
They are in the liquid or gaseous state at room temperatureThey are in solid-state
e.g. HCl, etc..e.g. NaCl, etc.

Coordinated or Dative Covalent Bond: This type of bond occurs when one of the atoms in the bond provides electrons for sharing. This is accomplished through the reaction of ammonia and boron trifluoride. Nitrogen has two free electrons, whereas boron lacks electrons. They complete their last shell with eight electrons by combining nitrogen and boron.



Sample Questions

Question 1: Why do atoms react and how?

Answer:

Atoms with eight electrons in their final orbit are stable and do not react. Atoms with fewer than eight electrons react with other atoms to gain eight electrons in their outermost orbit and thus become stable. Atoms with slightly more than eight electrons may lose them to atoms with fewer than eight. Atoms that cannot lose or gain may share to obtain an octet configuration. Even after the reaction, molecules lacking an octet configuration may accept a lone pair of electrons from other atoms or molecules.

Question 2: What are hybridized orbitals?

Answer:

Relatively similar energy sub-orbitals can merge to form a new set of the same number of orbitals, with the property of all contributing orbitals being proportional to their numbers. These orbitals are called hybridised orbitals.

Question 3: What is Dative Covalent Bond?

Answer:

This type of bond occurs when one of the atoms in the bond provides electrons for sharing. This is accomplished through the reaction of ammonia and boron trifluoride. Nitrogen has two free electrons, whereas boron lacks electrons. They complete their last shell with eight electrons by combining nitrogen and boron.

Question 4: What is bond enthalpy?

Answer:

The chemical bonding between atoms causes energy to be released when they come close together. Bond dissociation enthalpy or Bond enthalpy is the amount of energy required to break one mole of a type of bond in order to separate the molecule into individual gaseous atoms.


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