Question

Arrange the bonds in each of the following sets in order of increasing polarity: (a) \(\mathrm{C}-\mathrm{F}, \mathrm{O}-\mathrm{F}, \mathrm{Be}-\mathrm{F}\); (b) \(\mathrm{O}-\mathrm{Cl}, \mathrm{S}-\mathrm{Br}, \mathrm{C}-\mathrm{P}\); (c) \(\mathrm{C}-\mathrm{S}, \mathrm{B}-\mathrm{F}, \mathrm{N}-\mathrm{O}\).

Short answer

The bonds arranged in increasing order of polarity are as follows: (a) \(\mathrm{O}-\mathrm{F}, \mathrm{C}-\mathrm{F}, \mathrm{Be}-\mathrm{F}\) (b) \(\mathrm{O}-\mathrm{Cl}, \mathrm{C}-\mathrm{P}, \mathrm{S}-\mathrm{Br}\) (c) \(\mathrm{C}-\mathrm{S}, \mathrm{N}-\mathrm{O}, \mathrm{B}-\mathrm{F}\)

Step-by-step solution

Electronegativity difference

To determine the polarity of a bond, we will analyze the electronegativity difference between the atoms involved in each bond.$$ \\ \mathrm{Electronegativity \ difference} = | \mathrm{Electronegativity} _{1} - \mathrm{Electronegativity} _{2} |$$

(a) $\mathrm{C}-\mathrm{F}, \mathrm{O}-\mathrm{F}, \mathrm{Be}-\mathrm{F}$;

First, we need the electronegativity values for C, O, Be, and F. Using a periodic table or electronegativity chart, we obtain: C (2.55), O (3.44), Be (1.57), F (3.98) Calculating the electronegativity difference for each bond: $$ | \mathrm{C} - \mathrm{F} | = | 2.55 - 3.98 | = 1.43 $$ $$ | \mathrm{O} - \mathrm{F} | = | 3.44 - 3.98 | = 0.54 $$ $$ | \mathrm{Be} - \mathrm{F} | = | 1.57 - 3.98 | = 2.41 $$ Thus, arranging the bonds in increasing polarity order: \(\mathrm{O}-\mathrm{F}, \mathrm{C}-\mathrm{F}, \mathrm{Be}-\mathrm{F}\).

(b) $\mathrm{O}-\mathrm{Cl}, \mathrm{S}-\mathrm{Br}, \mathrm{C}-\mathrm{P}$;

The electronegativity values for Cl, S, Br, and P are: Cl (3.16), S (2.58), Br (2.96), P (2.19) Calculating the electronegativity difference for each bond: $$ | \mathrm{O} - \mathrm{Cl} | = | 3.44 - 3.16 | = 0.28 $$ $$ | \mathrm{S} - \mathrm{Br} | = | 2.58 - 2.96 | = 0.38 $$ $$ | \mathrm{C} - \mathrm{P} | = | 2.55 - 2.19 | = 0.36 $$ Arranging the bonds in increasing polarity order: \(\mathrm{O}-\mathrm{Cl}, \mathrm{C}-\mathrm{P}, \mathrm{S}-\mathrm{Br}\).

(c) $\mathrm{C}-\mathrm{S}, \mathrm{B}-\mathrm{F}, \mathrm{N}-\mathrm{O}$;

The electronegativity value for B and N are: B (2.04), N (3.04) Calculating the electronegativity difference for each bond: $$ | \mathrm{C} - \mathrm{S} | = | 2.55 - 2.58 | = 0.03 $$ $$ | \mathrm{B} - \mathrm{F} | = | 2.04 - 3.98 | = 1.94 $$ $$ | \mathrm{N} - \mathrm{O} | = | 3.04 - 3.44 | = 0.40 $$ Arranging the bonds in increasing polarity order: \(\mathrm{C}-\mathrm{S}, \mathrm{N}-\mathrm{O}, \mathrm{B}-\mathrm{F}\).

Key concepts

Electronegativity

Electronegativity is a crucial concept in understanding chemical bonds and their polarity. It is a measure of an atom's ability to attract and hold onto electrons when it forms a chemical bond.

Elements on the periodic table have varying levels of electronegativity, usually resulting from both their atomic number and their distance from the nucleus. The most electronegative element is fluorine, which serves as a benchmark for comparing the electronegativity of other elements.

When two atoms form a bond, the difference in their electronegativity values can predict whether a bond will be ionic, covalent, or polar covalent. An ionic bond occurs when the difference is significant, and electrons are transferred from one atom to the other. A covalent bond forms when the difference is small or nonexistent, and electrons are shared equally. In between these extremes is the polar covalent bond, where electrons are shared unequally, leading to a dipole moment - a key feature of polar molecules.

Chemical Bonds

Chemical bonds are the glue that holds atoms together in molecules. There are primarily three types of chemical bonds: ionic, covalent, and metallic. Ionic bonds form between metals and nonmetals, where there is a transfer of electrons. Covalent bonds typically form between nonmetals, where electrons are shared.

Polarity in Bonds

The concept of polarity arises particularly in covalent bonds, where the sharing of electrons can be unequal if one atom is more electronegative than the other. This results in a partial charge distribution, where one end of the bond becomes partially positive and the other end becomes partially negative. This characterizes a dipole, with a ‘+’ side and a ‘-’ side, and is the essence of bond polarity. The greater the difference in electronegativity, the more polar the bond will be.

Polarity Order

Polarity order refers to the ranking of chemical bonds by their polarity, which is based on the electronegativity difference between the bonded atoms. Understanding polarity order is essential when predicting the behavior of molecules in different environments, such as in water or when forming crystal lattices.

In order to compare the polarity of different bonds, a scientist or student can calculate the difference in electronegativity values between two bonded atoms using the formula:
\[ | \text{Electronegativity of atom 1} - \text{Electronegativity of atom 2} | \] Bonds can then be arranged from least to most polar, by comparing these differences for each pair. The bond with the smallest electronegativity difference is the least polar, while the one with the largest difference is the most polar. This systematic approach helps in studying various chemical properties like solubility, reactivity, and molecular interactions.