What do you mean by Polarity of Bonds? Sounds difficult? Well, it is not! Have you played the “tug-of-war” game? Similar to the game of “tug-of-war”, in chemistry when two atoms share a pair of electrons, they try to pull it towards themselves. This gives rise to the concept of bond polarity. However, before we get into the details of the chapter, let us first know what polarity is.
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Polarity of Bonds
Polarity refers to the physical properties of compounds such as boiling point, melting points and their solubilities. The polarity of bonds is caused due to the interaction of the bonds between molecules and atoms with different electronegativities.
Consider an electromotive force (EMF) or an electric potential, acting between two points. Here, the points or poles have a greater number of electrons than the other. The pole that has more electrons possesses a negative polarity whereas the other end possesses a positive polarity.
Polarity in Chemistry is nothing but the concept of the separation of an electric charge leading a molecule to have a positive and negative end. Consider the below example:
In an H-F bond, the fluorine atom is more electronegative than that of the Hydrogen atom. The electrons eventually spend more time at the Fluorine atom. Hence, this F atom slightly becomes negative whereas the Hydrogen atom tends to become slightly positive.
Browse more Topics under Chemical Bonding And Molecular Structure
- Bond Parameters
- Covalent Compounds
- Fundamentals of Chemical Bonding
- Hybridisation
- Hydrogen Bonding
- Ionic or Electrovalent Compounds
- Molecular Orbital Theory
- Resonance Structures
- Valence Bond Theory
- VSEPR Theory
Definition of Polarity
“A state or a condition of an atom or a molecule having positive and also negative charges, especially in case of magnetic or an electrical poles.”
Polarity Of Molecules
The bond or the molecular polarities are related to the electronegativities of the atoms or the molecules. A molecule can basically be either polar molecule, non-polar molecule or an ionic molecule.
Polar Molecules
A polar molecule usually forms when the one end of the molecule is said to possess a number of positive charges and whereas the opposite end of the molecule has negative charges. Thus, they end up creating an electrical pole. In a molecule having a polar bond, the centre of the negative charge will be on one side. Whereas the centre of positive charge will be on the different side. The entire molecule will be a polar molecule.
Non- Polar Molecules
A molecule which does not have the charges present at the end due to the reason that electrons are finely distributed and those which symmetrically cancel out each other are the non- polar molecules. In a solution, we cannot mix a polar molecule with the non-polar molecule. For example, consider water and oil. In this solution, water is the polar molecule. On the other hand, oil behaves as a non-polar molecule. These two molecules do not form a solution. This is because they cannot ever be mixed up.
Examples of Polar and Nonpolar Molecules
A molecule may be polar or Non-polar. A non-polar molecule has the structure of its atoms lined up in a way that the orbital electrons in the outer region cancel out the electronegativity. In general, pyramid-shaped and V-shaped molecules are said to be polar. Whereas the Linear molecules said to be non-polar in nature.
Water is said to be a polar molecule due to the difference in the electronegativities between the oxygen atom and the hydrogen. Oxygen is a highly electronegative atom when compared to hydrogen. Fats, petrol, oil, gasoline are said to be non-polar molecules as they do not dissolve in water and nonpolar are insoluble in water. Glucose is another such example of a polar molecule. It is based on the arrangement of the oxygen and hydrogen atoms in it.
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Factors on which the Polarity of Bonds Depends
1) Relative Electronegativity of Participating Atoms
Since the bond polarity involves pulling of electrons towards itself, hence a more electronegative element will be able to attract the electrons more towards itself. As a result, the electrons will definitely move towards the more electronegative element. The amount of their shifting will depend upon the relative electronegativity of the participating atoms.
2) The Spatial Arrangement of Various Bonds in the Atom
The shared pair of electrons also experience pulling force from the other bonded and non-bonded pair of electrons. This results in different bond polarity between same participating atoms that are present in different molecules. For e.g. Bond Polarity of O-H bond in a water molecule and acetic acid molecule is different. This is due to the different spatial arrangement of various bonds in the molecule.
Solved Example for You
Q: The electronegativity of C,H,O,N and S are 2.5, 2.1, 3.5, 3.0 and 2.5 respectively. Which of the following bond is most polar?
A) O – H B) S – H C) N – H D) C – H
Solution: A) If the difference in the electronegativity between two or more atoms is more, the bond between them is more polar. For the given atoms, we can see that:
- O – H = 3.5 – 2.1 = 1.4
- S – H = 3.5 – 2.5 = 1
- N – H = 3.0 – 2.1 = 0.9
- C – H = 2.5 – 2.1 = 0.4 .
Therefore, the O-H bond is the most polar among the given bonds.
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