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Polarity - Definition, Uses, Examples, Bond Polarity, Factors Affecting the Bond Polarity, Practice Problems & FAQs

Isn't it true that we've all played tug-of-war?

Can you guess who will be the winner by looking at the image below?

Please enter alt text

Of course, the stronger man will win the game since he has more strength and energy. A similar principle applies in chemistry if we talk about polarity.

So, let's have a look at the concept of polarity

Table of Contents

  • What is Polarity?
  • Polarity of Molecules
  • Factors Affecting the Bond Polarity
  • Practice Problems
  • Frequently Asked Questions- FAQs

What is Polarity?

Polarity is the state of an atom (or a molecule) that has both the electrical poles, positive and negative charges. Polarity is the separation of electric charges in chemistry, which results in a positive and negative pole or end. If there is a highly distinct separation of charges, we consider that there is extreme separation in the atom. On one pole, there are more electrons than on the other. The pole with the most electrons is polarised negatively, while the pole with the fewest electrons is polarised positively.

The separation of a charge within a molecule is referred to as bond polarity. The dipole moment of the chemical bond is used to calculate the bond polarity. When the electronegativities of the two elements in a chemical bond differ, the linked electrons are pushed towards the more electronegative element. The polarity of the molecule is determined by the polarity of the link.

The physical properties of compounds, such as solubility, melting points, and boiling points, are all influenced by polarity. In the domains of electricity, magnetism, and electrical device signalling, we frequently use polarity.

The polarity between the bonds comes from the act of molecules and atoms that have various electronegativities (a measure of the tendency of an atom to attract the shared electrons towards itself in a covalently bonded molecule). The greater the electronegativity, the greater the polarity of the bond.

This can clearly be understood by the animation given below:

In case H2 molecule, H—H bond is not polar as both the hydrogen atoms have exactly the same electronegativity value. On the other hand, in the case of H—F bond, the fluorine atom is more electronegative than the hydrogen atom. As a result, the electrons are drawn more towards the fluorine atom than toward the hydrogen atom. As a result, the hydrogen atom is partially positive, while the fluorine atom is partially negative.

If the polarity of bonds between hydrogen and other atoms (which are shown in the animation) is compared, then the order of polarity would be:

H—H < H—C < H—O < H—F

The reason for this order of polarity of bond is the electronegativity order of the atoms bonded with the hydrogen atom. The order of electronegativity is:

H < C < O < F

Polarity of Molecules

The molecular polarity of bonds is determined by the electronegativities of bonded atoms. Molecules are said to be polar, non-polar, or ionic depending upon the type of bonds formed.

Polar molecules:

A molecule is said to be polar if it has more positive charges on one end and fewer negative charges on the other and vice-versa. This polarity generates an electrical pole or dipole. The negative charge's centre will be on one side of a polar molecule, while the positive charge's centre will be on the other.

Examples of polar molecules: HF, HCl, H2O etc.

Non-polar molecules:

When a molecule's electrons are spread throughout the molecule and the molecules are symmetrical, either due to the same electronegativity of the atoms or if the resultant dipole moment cancels out, we call those molecules non-polar.

Examples of non-polar molecules: H2, F2, Cl2 etc.

Ionic molecules:

If a molecule contains only one form of charge, it is said to be ionic. The charge can either be positive or negative.

When electrons are transferred from one element's atoms to another element's atoms, positive and negative ions are produced, resulting in the closest noble gas configuration (octet rule). An electrostatic force of attraction exists between positively charged cation and negatively charged anion due to the production of charged ions, resulting in the establishment of an ionic bond. Electrovalent bonds are another name for them. These bonds are non-directional because they are produced by the transfer of electrons. So, the most polar bonds are the ionic bonds as the difference in the electronegativity values between atoms is huge.

For example;

NaNa++e-

Cl+e-Cl-

Na++Cl-NaCl

Factors Affecting the Bond Polarity

The following are the factors which affect the polarity of bonds between atoms/molecules:

  • The relative electronegativity of the atoms or molecules that take part in the formation of a bond. The more the electronegativity difference between atoms more will be the bond polarity.
  • The spatial arrangement of the different bonds that exist in the molecule. The electrons which are shared also experience force from the other pair of electrons which can be bonded or non-bonded. Due to this bond polarity is different between the same atoms that are present in different molecules. Example: Bond polarity of the N-H bond in an ammonia molecule and in methyl amine molecule is different. This happens due to the different spatial arrangements of different bonds in the molecule.

Practice Problems

Question: Which of the following compounds has the greatest degree of polarity?

  1. HBr
  2. HI
  3. HCl
  4. HF

Answer: (D)

Solution:

Polarity is defined as the difference in electronegativity between two covalently bonded atoms. HF is the most polar molecule due to the significant difference in electronegativity values between the H and F atoms. As fluorine atom is the most electronegative atom if compared with chlorine, bromine and iodine. As a result, option D is the correct answer.

Question: Which of the following compounds is non-polar?

  1. HBr
  2. PF3Cl2
  3. C6H6
  4. CH3OH

Answer: (C)

Solution:

The Lewis structure of benzene is C6H6 looks like this:

The net dipole moment of the benzene molecule is zero. So, it is a non-polar molecule.

So, option C is the correct answer.

Question: On the Pauling scale, the electronegativity values of A, B and C are 2, 3 and 4 respectively. Out of two compounds A—B and A—C, which one is more polar?

Answer:

The electronegativity difference between A—B is 1 and the electronegativity difference between between A—C is 2. The electronegativity difference value is more in A—C compound. So, A—C is more polar than A—B.

Frequently Asked Questions - FAQs

Question: Can a compound have both polar and nonpolar covalent bonds?
Answer:
In H2O2, electronegativity difference between O and 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. So, H2O2 molecule

Question: What is electronegativity?
Answer:
Electronegativity is the tendency of an atom in a molecule to attract the shared pair of electrons towards itself. The electron cloud is more towards the more electronegative atom in a diatomic molecule.

Question: What effect does polarity have on solubility?
Answer:
Similar polarity substances are usually soluble in one another ("like dissolves like"). Polar and ionic chemicals are more soluble in polar solvents, while non-polar substances are more soluble in non-polar solvents.

Question: What causes polarity to produce?
Answer:
In practice, rather than being calculated, the polarity of a bond is frequently assumed. With increasing electronegativity differences between the atoms which are bonded, bond polarity and ionic character rise. So, the major reason for a bond to attain polarity is the electronegativity difference between the atoms which are bonded.

Question: Which bonds are the most polar?
Answer:
Ionic bonds are most polarised because electrons are transferred rather than shared. So, ionic bonds are the most polar bonds among all the types of bonds.

 

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