Polarity: Polar Vs Non-Polar Molecules with Examples

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Polarity in chemical bonding refers to the state that involves the separation of electric charges resulting in the formation of dipole moment, with a negative and positive charge on the ends of the poles.

This phenomenon arises due to the difference in the electronegativity of atoms in a bond.
In a bonded atoms, the more electronegative atom will attract the electron cloud towards it thereby making the bond polar.
Polarity depends upon factors such as surface tension, boiling point, melting point, and solubility of the compounds.
The property of molecules depends upon factors like the type of atoms and the type of bonds between atoms.
Its applications can be seen in the fields of electricity, magnetism, chemistry and electronic signalling, describing the flow of electrons.

Table of Content

Define Polarity
Polarity of Molecules
Polarity of Bonds
Factors affecting Bond Polarity
Things to Remember
Sample Questions

Key Terms: Polarity, Dipole Moment, Polar Molecules, Non-Polar Molecules, Electronegativity, Atoms, Charge, Molecules, Covalent Bonds

Define Polarity

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Polarity indicates the degree of uneven distribution of charge between molecules which interact through dipole-dipole intermolecular forces and hydrogen bonds.

The atom having high electronegativity will pull the electrons having low electronegativity.
Polarity helps us understand how molecules interact and dissolve in the solution.
The concept provides a deeper insight into the chemical structures of molecules and their reactions.
You can understand polarity by using the concept of electromotive force (EMF) or electric potential acting between two poles.
In this case, the end with more electrons is negatively polarized, while the end with fewer electrons is positively polarized.

Polarity Example

Consider the compound hydrogen fluoride, where fluorine is more electronegative than a hydrogen atom. More electrons will be found at fluorine atoms than at hydrogen atoms, making fluorine electronegative and hydrogen electropositive.

Polarity of H₂O

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Polarity of Molecules

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The polarity of molecules depends upon the electronegativity and electropositivity of atoms or molecules. The molecular polarity is divided into two categories which are as follows:

Polar Molecules

Polar molecules are generated when one end of the molecule tends to have more positive charges than the other end. This results in the formation of a polar covalent bond.

When a polar bond is formed between molecules, then the molecule bearing a negative charge will be on one side, while the molecule bearing a positive charge will be on the other side.
This difference in electronegativity between atoms bearing charges results in the formation of polar molecules.
The shapes of polar molecules are pyramid-shaped and V-shaped.

Examples of Polar Molecules

Some common examples of polar molecules are as follows:

Water: Water is a polar molecule that consists of an uneven distribution of charge between hydrogen and oxygen atoms, which results in the formation of a net dipole moment.
Ammonia: Ammonia is another example of a difference in electronegativity between hydrogen and nitrogen that will lead to the formation of a polar covalent bond.

Non-Polar Molecules

The polarity of molecules will result in the formation of non-polar molecules when charges found at the both end molecules are uniformly distributed. This will generate a symmetrical structure of atoms, resulting in the absence of a net dipole moment.

Examples of Non-Polar Molecules

Some common examples of non-polar molecules are as follows:

Methane: Methane is a non-polar molecule with four similar carbon-hydrogen bonds that form symmetrical tetrahedral structure with no net dipole moment.
Carbon Dioxide: Despite having polar covalent bonds, carbon dioxide forms a symmetrical linear distribution of molecules.

Polarity of Bonds

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The polarity of bonds refers to the uneven distribution of electrons between the bonded atoms, which leads to the formation of partial positive and negative charges on the respective atoms.

The bond polarity is affected by the polarity of molecules.
It involves the separation of charge between atoms by unequal sharing of electrons.
The bond is characterized by an arrow that points towards the more electronegative atom.
This means that an electronegative atom will attract more number of shared electrons.

Factors affecting Bond Polarity

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The factors affecting the polarity of bond are as follows:

Electronegativity Difference

The electronegativity of an atom is determined by its ability to hold and attract an electron participating in bond formation. When two atoms form a covalent bond, the electrons are attracted toward more electronegative atoms. This results in the formation of a negative charge on more electronegative atoms and a positive charge on less electronegative atoms.

Molecular Geometry

The arrangement of atoms in a molecule determines the bond polarity. In the case of symmetrical molecular geometry, bonds between the molecules are nonpolar as the zero net dipole is created as bonds cancel out each other. Similarly, in case of asymmetricalrical molecular geometry, bonds between the molecules will result in the formation of a net dipole moment.

Things to Remember

The polarity of molecule is determined by the value of the net dipole moment of the molecule.
Atoms with negligible electronegativity differences combine to form non-polar molecules.
The polarity of a bond is determined by the electronegativity difference between the bonded pair of atoms.
The greater the electronegativity difference, the higher will be the polarity of the bond.
The topic of polarity comes under the unit chemical bonding and molecular structure which carries 6 marks for the CBSE exams.

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Sample Questions

Ques: Answer the following: (A) Which molecule is more polar, NH₃, or NF₃?
(B) Arrange the given molecules in their increasing order of polarity: HF, HI, HCl, and HBr? (2 marks)

Ans: (A) Even though the N-F bond is more polar than the N-H bond, from the net dipole moment we can infer that NH₃ is more polar than NF₃.

(B) The order for the molecules in increasing order of polarity are as follows: HI<HBr<HCl<HF

Ques: What is the value of net dipole moment in linear molecules? Illustrate with an example. (2 marks)

Ans: In the case of linear molecules, the individual dipole moments cancel each other and make the net dipole moment zero. Similarly in the case of CO₂, the C-O bond is polar due to the higher electronegativity of oxygen compared to carbon. But the individual dipole moments cancel each other since they are opposite in direction and hence the net dipole moment of the molecule becomes zero.

Ques: Calculate the percentage ionic and covalent character in HF molecules having bond distance = 0.92A and dipole moment=1.78D? (4 marks)

Ans: Given, µ(observed) = 1.78D= 1.78 x 10^-18 esu.cm

r = 0.92A = 0.92 x10^-8 cm

We know,

% ionic character = (µ(observed)/µ(theoretical))*100

Also,

µ(theoretical) = Q x r, (Q= charge of electron)

Now,

% ionic character = (1.78 x10^-18esu.cm)/ (4.8 x10^-10esu x 0.92 x10^-8cm) = .403 = 40.3%

Ionic character = 40.3%

Hence, Covalent character = 100 – 40.3 = 59.3%

Ques: Why all the molecules with polar covalent bonds are not polar? Justify? (2 marks)

Ans: The presence of polar covalent bonds does not account for the polarity of molecules. The polarity of a molecule is determined using dipole moment. Molecules with a net dipole moment are only counted as polar molecules, molecules with zero net dipole moment are counted as non-polar molecules.

Ques: What is the difference between polar and non-polar molecules? (4 marks)

Ans: The difference between polar and non-polar molecules are as follows:

Polar Molecules	Non-Polar Molecules
Polar molecules involves uneven distribution of electrons.	Non-polar molecules involves uniform distribution of electrons.
These molecules have high melting and boiling point.	These molecules have low melting and boiling point.
They have a net dipole momemt.	They have zero dipole moment.
In polar molecules charge are separated between molecules.	In non-polar molecules charge are not separated between molecules.

Ques: What is dipole momemt? (3 marks)

Ans: Dipole moment is defined as the product of the magnitude of charge and the distance of separation between the centres of positive and negative charge. It is a vector quantity and it is denoted by µ.

µ = charge (Q) * Distance of separation(r)

The dipole moment is expressed in Debye units (D). It will have both magnitude and direction. The moment is denoted using an arrow with the tail towards the positive charge and the head towards the negative charge.

Ques: What is polar covalent bonds? (3 marks)

Ans: When a covalent bond is formed between two atoms with considerable differences in electronegativity values, such types of bonds are called polar covalent bonds. In these bonds, the shared pair of electrons will get displaced towards the highly electronegative atom. The greater the electronegativity between the bonding atoms, the higher will be the polarity of the bond.

Consider an HCl molecule, H – Cl, due to the high electronegativity of Chlorine, the shared pair of electrons will get displaced towards chlorine, and thereby chlorine will acquire a partial negative charge (δ-) and hydrogen will acquire a partial positive charge (δ+).

Ques: What is non-polar covalent bonds? (3 marks)

Ans: A covalent bond is said to be nonpolar if the bonding pair of atoms are of similar electro-negativity. The shared pair of electrons will be equidistant from both atoms.

Diatomic molecules like H₂, O₂, and N₂ are examples of molecules with nonpolar covalent bonds.
The molecules with nonpolar covalent bonds are regarded as Non-Polar Molecules.
Alkanes are also regarded as non-polar molecules since the electronegativity difference between Carbon and Hydrogen is negligible.

Ques: Calculate the percentage ionic and covalent character in HF molecules having bond distance = 0.9A and dipole moment=1.78D? (4 marks)

Ans: Given, µ(observed) = 1.78D= 1.78 x10^-18 esu.cm

r = 0.9A = 0.9 x10^-8 cm

We know,

% ionic character = (µ(observed)/µ(theoretical))*100

Also,

µ(theoretical) = Q x r, (Q= charge of electron)

Now,

% ionic character = (1.78 x10^-18esu.cm)/ (4.8 x10^-10esu x 0.9 x 10^-8cm) = 0.412 = 41.2%

Ionic character = 41.2%

Hence, Covalent character = 100 – 41.2 = 58.8%

Ques: What is polarity and polarisation? (3 marks)

Ans: In chemistry, polarity refers to the uneven electrical charge distribution within a molecule. This arises due to differences in electronegativity, the attraction an atom has for electrons in a chemical bond.

Polarization can also refer to the alignment of electric dipoles (regions of positive and negative charge) in a material under the influence of an external electric field.
This can happen in dielectrics, materials that don't conduct electricity but can store electrical energy in an electric field.

Ques: What is the cause of polarity? (3 marks)

Ans: The main cause of polarity in molecules is the uneven sharing of electrons between bonded atoms, which arises from a property called electronegativity. The factors affecting the polarity are as follows:

Electronegativity: This is the tendency of an atom in a molecule to attract electrons towards itself in a chemical bond. Different elements have different electronegativity values.
Unequal Sharing: When two atoms with different electronegativity values form a covalent bond, they don't share the electrons equally. The more electronegative atom pulls the shared electrons closer to its nucleus, creating a slightly negative region around it. The other less electronegative atom experiences a slight positive charge because it loses some electron density.

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Polarity: Polar Vs Non-Polar Molecules with Examples