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Covalent Bonding - Covalency, Formation, Properties, Types, Examples, Practice problems & FAQs

We've seen bees fly from flower to flower in search of nectar. Bees convert this nectar into food for themselves and simultaneously they are transferring pollen particles that have adhered to their bodies from another flower to the flowers on which they are sitting which results in plant pollination. So, we can say that both bees and plants are getting benefits from each other. The same happens in chemistry as well when we talk about covalent bonds where atoms get benefits from each other just by mutual sharing of electrons. Let’s see how covalent bonds are formed.


Table of content:

Covalent bond

A Covalent bond is formed by a shared pair of electrons from both the participating atoms. The atoms will reach stability in their outer shell, comparable to noble gas atoms, as a result of this electron pair sharing.

This process when an element shares its electrons with another element (same or different) to acquire a stable electronic configuration, it is called covalency. 

For example, in H2, both the hydrogen atoms will share one electron each to acquire a stable electronic configuration, so its covalencey is 1.


Atoms with high ionization energy and low electron affinity are not able to lose or gain electrons easily. Due to this reason such elements share electrons to achieve noble gas configuration and attain stability. Such association through the sharing of electrons is known as the Covalent Bond.

Formation of covalent bonds

Covalent bonding can be achieved in two ways:

  • Sharing of electrons between atoms of the same kind e.g., H2,Cl2, etc.


  • Sharing of electrons between atoms of different kind e.g., CH4, H2O, etc.


Properties of covalent bond

Some of the properties of covalent bonds are:

  • Because of the lack of free electrons, covalently bonded compounds do not conduct electricity.
  • Generally covalent compounds are not soluble in water.  
  • They are strong chemical bonds that exist between atoms.
  • Most covalently bonded compounds have relatively low melting and boiling points.
  • Compounds with covalent bonds usually have a lower enthalpy of vaporization (heat consumed or discharged when matter disintegrates, changing state from fluid to gas state at a consistent temperature) and enthalpy of fusion (heat consumed or discharged when matter melts, changing stage from solid to fluid-structure at a consistent temperature.)

Types of Covalent bonds


Single covalent bond

A single bond is formed when two participating atoms share only one pair of electrons. It is denoted by a single dash (-). Here, sigma bond (formed by head-on overlapping of hybrid orbitals (along the bonding axis) formation will take place.

For example,  H2 molecules have two hydrogen atoms sharing one electron each to achieve noble gas configuration. In this case, a single bond is formed between hydrogen and hydrogen.


Double covalent bond

When only two pairs of electrons are shared by the two participating atoms, a double bond is formed. It is denoted by two dashes (-). Here, along with sigma bond, pi bond (formed by side-to-side overlapping of hybrid orbitals (above and below the bonding axis) will also form.

For example: Each oxygen atom has six electrons in its valence shell during the formation of the O2 molecule. Each atom requires two more electrons to complete its octet. As a result, two  pair of electrons are shared by the atoms to form the oxygen molecule. The two oxygen atoms form a double bond because they share two electron pairs.


Triple covalent bond

When only three pairs of electrons are shared by the two participating atoms, a triple bond is formed. It is denoted by three dashes (-).  It is the strongest bond among single, double & triple bonds.

For example: Each Nitrogen atom has five electrons in its valence shell. To complete their octet, each atom requires three more electrons. As a result, the atoms share three electrons to form the nitrogen molecule N2 . 

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. As a result, the shared electron pair will be located closer to that atom.

Example: Consider H and Cl, which have an electronegativity difference that is greater than zero and have a covalent bond between them. Shared pair of electrons move toward a high electronegative Chlorine atom.

This ‘Cl’ receives a partial negative charge and 'H' receives a partial positive charge, with two charges (poles are formed, and this is known as a Dipolar molecule or Dipole or Polar covalent molecule). 

Non-polar 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 (diatomic elements).

Example: Nonpolar Covalent Bond is found in gas molecules like Hydrogen gas, Nitrogen gas, chlorine gas etc.

Practice problems

Question 1. Show covalent bond formation in C2H2.

Answer: We know,

Electronic configuration of H= 1s1

Electronic configuration of C= 1s22s22p2

H need one more electron to complete its stable electronic configuration whereas C need 4 electrons. 

Both the carbons will share 3 electrons each with each other forming triple covalent bond between carbon and carbon and each carbon will share one-one electron with hydrogen forming single covalent between between hydrogen and carbon as shown below.


Question 2. Which of the following molecules is the most polar?

a. HCl
b. H2Se
c. CH4
d. HI

Answer: The greater the difference in electronegativity between two covalently bonded atoms, the greater the polarity. Because of the large difference in electronegativity between the H and Cl atoms in HCl, it is the most polar compound. So, option A is the correct answer.

Question 3. The number of types of bonds between two carbon atoms in calcium carbide is:

a. One sigma, two pi
b. One sigma, one pi
c. Two sigma, one pi
d. Two sigma, two pi

Answer: We know that the formula of calcium carbide is CaC2

In this compound, both ionic and covalent bond is formed. The bond between the two carbon atoms is covalent. However, the bond between Ca2+ and C2- is ionic.

Now, if you carefully look at the bonding between two carbon atoms, it consists of two carbon atoms connected by a triple bond i.e., one sigma bond and two pi bonds with each carbon atom carrying an additional lone pair. So, option A is the correct answer.


Question 4.  What are the differences between covalent and ionic bonds?

Answer:

Covalent bonds Ionic bonds
Formed between two similar electronegative non-metals Formed between a metal and a non-metal
Have a definite shape Have no definite shape
Low melting and boiling point High melting and boiling point
Low polarity and more flammable High polarity and less flammable
At room temperature, covalent bonds are in liquid or gaseous state 

At room temperature,

ionic bonds are in solid state 

Example: Methane, Hydrochloric acid Example: Sodium chloride, Potassium iodide

Frequently asked questions-FAQ

Question 1. Can a compound have both polar and nonpolar covalent bonds?

Answer: In H2O2 , electronegativity difference between O and the H atom is 1.4, so the 

O – H bond is polar whereas the electronegativity difference between O and O bond is zero, so the O – O bond is nonpolar.

Question 2. What is the difference between valency and valence electrons?

Answer: Valence electrons are the electrons that are usually located in the outermost shell of an atom. e.g: the electronic configuration of nitrogen is 1s22s22p3 So, here in the outermost shell, 5 valence electrons are present. 

Valency, on the other hand, is the combining capacity of an atom. 

Considering the case of Nitrogen whose electronic configuration is 1s22s22p3, its needs 3 more electrons to attain a stable electronic configuration. As it is gaining 3 electrons so we can say that its valency is 3.

Question 3.  What is electronegativity?

Answer: Electronegativity is the tendency of an atom in a molecule to attract the shared pair of electrons towards itself.

Question 4.  Is it possible for a compound to have both covalent and ionic bonds?

Answer: Yes, both covalent and ionic bonds can exist in a same compound.

For example; Na3PO4 is an ionic compound because sodium is a metal and the phosphate ion (PO3-) is a polyatomic ion. But covalent bond is holding this polyatomic ion (PO3-) together whereas ionic bond is forming between Na+ and PO3+. So, we can say that this compound contains both ionic and covalent bonds.

Related Topic

Ionic bonding Fajan's rule - Ionic character of covalent bond
Chemical bonding Lewis dot structure
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