Question

For each of the questions, four choices have been provided. Select the correct alternative. Which of the following bonds is more polar when compared to others? (a) \(\mathrm{O}-\mathrm{H}\) (b) \(\mathrm{N}-\mathrm{H}\) (c) \(\mathrm{C}-\mathrm{H}\) (d) \(\mathrm{H}-\mathrm{H}\)

Short answer

Answer: The most polar bond among the options provided is the (a) O-H bond.

Step-by-step solution

Recall the electronegativity values of the elements given

Electronegativity values are not equal for all elements. In this exercise, we are working with hydrogen (H), oxygen (O), carbon (C), and nitrogen (N). The respective electronegativities of these elements are (in the Pauling scale): - Hydrogen (H): 2.20 - Oxygen (O): 3.44 - Nitrogen (N): 3.04 - Carbon (C): 2.55

Compute the difference in electronegativity for each bond

Calculate the absolute value of the difference in electronegativity for each bond. This will give us the polarity for each bond. The larger the difference, the more polar the bond is. (a) O-H bond: |3.44 - 2.20| = 1.24 (b) N-H bond: |3.04 - 2.20| = 0.84 (c) C-H bond: |2.55 - 2.20| = 0.35 (d) H-H bond: |2.20 - 2.20| = 0

Identify the bond with the largest difference in electronegativity

From the calculated values in step 2, we see that the O-H bond has the largest difference in electronegativity (1.24). Therefore, it is the most polar bond among the options provided.

Answer the question

Since the O-H bond has the largest difference in electronegativity values, the correct choice is (a) O-H bond.

Key concepts

Polarity of Bonds

Polarity in chemical bonds refers to the unequal distribution of electron density between two bonded atoms. This happens when the two atoms involved in a bond have different electronegativities. When one atom is more electronegative than the other, it pulls the shared electrons closer, creating a partial negative charge on itself and a partial positive charge on the other atom.

This leads to the formation of a dipole moment in polar bonds, which is a measure of the bond's overall polarity. The greater the difference in electronegativity between the two atoms, the more polar the bond will be. For example, the O-H bond is significantly polar due to the large electronegativity difference between oxygen and hydrogen. In contrast, a bond between two atoms of similar electronegativity, such as H-H, is non-polar, since the electrons are shared more equally.

Electronegativity

Electronegativity is a chemical property that measures an atom's ability to attract and hold onto electrons within a bond. Each element has a specific electronegativity value, and these values help predict how atoms will interact in a molecule.

An atom with a higher electronegativity will pull the shared electrons in a bond closer to itself, leading to an uneven distribution of charge. In other words, the atom with the higher electronegativity becomes slightly negative, while the other atom becomes slightly positive. This creates a polar bond.

Understanding electronegativity is essential for predicting bonding behavior and bond polarity, which are key concepts in chemistry. Generally, electronegativity increases across a period and decreases down a group in the periodic table.

Pauling Scale

The Pauling scale, introduced by Linus Pauling, is the most commonly used scale for measuring electronegativity. It assigns numerical values to elements based on their ability to attract electrons.

On this scale, the most electronegative element, fluorine, is given a value of 3.98, while francium, one of the least electronegative, has a very low value. The values help in calculating the polarity of bonds by providing a straightforward way of knowing the electronegativity differences between bonded atoms.

When using the Pauling scale:

• Be aware that large differences in electronegativity indicate polar bonds.
• Little to no difference indicates non-polar bonds.

This scale is fundamental in predicting molecular behavior and is widely used in both theoretical studies and practical applications in chemistry.

O-H Bond

The O-H bond is a classic example of a polar bond. This bond is formed between oxygen and hydrogen, two atoms with significantly different electronegativity values.

In the Pauling scale, oxygen has an electronegativity of 3.44, while hydrogen has a value of 2.20. The difference of 1.24 results in a highly polar bond. This polarity is why water, which contains O-H bonds, is such a good solvent for many ionic compounds and polar substances.

The polarity of the O-H bond contributes to water's high boiling point and its property as the "universal solvent." It allows water to dissolve many substances, making it vital for countless biological and environmental processes.