Question

The electronegativity values of \(\mathrm{C}, \mathrm{H}, \mathrm{O}, \mathrm{N}\) and \(\mathrm{S}\) are \(2.5,2.1,3.5,3.0\) and \(2.5\), respectively. Which of the following bonds is most polar? (1) \(\mathbf{C}-\mathrm{H}\) (2) \(\mathrm{N}-\mathrm{H}\) (3) \(\mathrm{S}-\mathrm{H}\) (4) O-H

Short answer

The \(\text{O-H}\) bond is the most polar.

Step-by-step solution

Understand Electronegativity

Electronegativity is the ability of an atom to attract electrons in a bond. The higher the electronegativity difference between two bonded atoms, the more polar the bond.

Identify Electronegativity Values

Retrieve the provided electronegativity values for each element involved: C: 2.5, H: 2.1, O: 3.5, N: 3.0, S: 2.5.

Calculate Electronegativity Differences

Determine the absolute difference in electronegativity values for each bond: (1) \(\text{C-H}: |2.5 - 2.1| = 0.4\), (2) \(\text{N-H}: |3.0 - 2.1| = 0.9\), (3) \(\text{S-H}: |2.5 - 2.1| = 0.4\), (4) \(\text{O-H}: |3.5 - 2.1| = 1.4\).

Identify the Most Polar Bond

Compare the electronegativity differences calculated in Step 3. The bond with the highest electronegativity difference is the most polar.

Conclusion

The \(\text{O-H}\) bond has the highest electronegativity difference of 1.4, making it the most polar bond among the given options.

Key concepts

Electronegativity Difference

Electronegativity difference is a key concept in understanding the behavior of chemical bonds. It refers to the difference in the ability of atoms to attract electrons within a bond.
When you compare the electronegativity values of two atoms, you can determine how the electrons are distributed.
A larger difference means a more uneven distribution, resulting in a more polar bond.
The electronegativity values of elements, such as those given for carbon (C), hydrogen (H), oxygen (O), nitrogen (N), and sulfur (S), help identify this difference.
For instance, if the value for hydrogen is 2.1 and oxygen is 3.5, subtracting these values (3.5 - 2.1 = 1.4) gives us the electronegativity difference. The greater this difference, the more polar the bond will be.

Polar Bonds

Polar bonds are a result of unequal sharing of electrons between two atoms in a molecule.
This inequality is a direct consequence of differing electronegativities. If one atom has a higher electronegativity, it will attract the shared electrons more strongly, making the bond polar.
For example, if we have an O-H bond, because oxygen (electronegativity = 3.5) attracts electrons more strongly than hydrogen (electronegativity = 2.1), the O-H bond becomes polar.
The direction of the bond polarity is indicated by the partial negative charge (δ-) on the more electronegative atom and a partial positive charge (δ+) on the less electronegative one. Polar bonds are critical in determining the physical properties of molecules such as solubility and boiling point.

Chemical Bonding

Chemical bonding is the process by which atoms combine to form compounds and molecules. There are several types of bonds, including ionic, covalent, and metallic bonds.
A covalent bond, where two atoms share electrons, is particularly influenced by electronegativity. When atoms with different electronegativities form a covalent bond, the electrons tend to spend more time closer to the atom with the higher electronegativity. This creates regions of partial positive and negative charges within the molecule, leading to a polar covalent bond.
The polarity of these bonds affects the molecule's overall shape and properties. For instance, water (H₂O) has polar bonds, which makes it an effective solvent for many substances. Understanding these bonds helps us predict and explain the behavior of substances in different chemical reactions.