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

(a) The order of increasing polarity is as follows: \(O-F < C-F < Be-F\) (b) The order of increasing polarity is as follows: \(O-Cl < C-P < S-Br\) (c) The order of increasing polarity is as follows: \(C-S < N-O < B-F\)

Step-by-step solution

Calculate electronegativity difference for each bond

C-F: \(|3.98 - 2.55| = 1.43\) O-F: \(|3.98 - 3.44| = 0.54\) Be-F: \(|3.98 - 1.57| = 2.41\)

Arrange the bonds in order

The order of increasing polarity is as follows: O-F < C-F < Be-F (b) Arrange the following bonds in order of increasing polarity: \(\mathrm{O}-\mathrm{Cl}, \mathrm{S}-\mathrm{Br}, \mathrm{C}-\mathrm{P}\)

Calculate electronegativity difference for each bond

O-Cl: \(|3.44 - 3.16| = 0.28\) S-Br: \(|2.58 - 2.96| = 0.38\) C-P: \(|2.55 - 2.19| = 0.36\)

Arrange the bonds in order

The order of increasing polarity is as follows: O-Cl < C-P < S-Br (c) Arrange the following bonds in order of increasing polarity: \(\mathrm{C}-\mathrm{S}, \mathrm{B}-\mathrm{F}, \mathrm{N}-\mathrm{O}\)

Calculate electronegativity difference for each bond

C-S: \(|2.55 - 2.58| = 0.03\) B-F: \(|3.98 - 2.04| = 1.94\) N-O: \(|3.04 - 3.44| = 0.40\)

Arrange the bonds in order

The order of increasing polarity is as follows: C-S < N-O < B-F

Key concepts

Electronegativity

Electronegativity is a fundamental concept in chemistry that explains how strongly an atom can attract a shared pair of electrons towards itself in a chemical bond. Each element has an electronegativity value on the Pauling scale, which can range from 0 to about 4. For example, fluorine is the most electronegative element with a value of 3.98.
Understanding electronegativity is crucial when predicting the nature of chemical bonds. Here's why it matters:

• When two different atoms form a bond, the atom with a higher electronegativity will attract the shared electrons more strongly.
• This difference in electronegativity leads to bond polarity, where the electron density is higher around the more electronegative atom.
• Electronegativity differences can predict whether a bond will be nonpolar covalent, polar covalent, or ionic.

When calculating the electronegativity difference, you simply subtract the smaller electronegativity value from the larger one for the two atoms involved in the bond. This difference can then indicate the degree of polarity in the bond.

Chemical Bonds

Chemical bonds are the glue that holds atoms together in molecules. They're formed because atoms have a tendency to achieve a more stable electron configuration. There are three main types of chemical bonds: ionic, covalent, and metallic, but we focus mainly on covalent bonds here, which involve the sharing of electron pairs between atoms.
Here's a quick breakdown:

• Covalent Bonds: These involve the sharing of electron pairs between atoms. Depending on the atoms' electronegativities, a covalent bond can be nonpolar (equal sharing) or polar (unequal sharing).
• Ionic Bonds: These occur when there is a complete transfer of electrons from one atom to another, typically between a metal and a non-metal. These are not the focus in polar covalent bonds but are at one end of the spectrum of electronegativity differences.

In covalent bonds, the behaviour of shared electrons is what dictates the bond's properties, including its polarity. Understanding chemical bonds helps predict molecular behavior and properties.

Polarity Order

The polarity order of chemical bonds is determined by the difference in electronegativity between the two bonding atoms. The greater the difference, the more polar the bond. This concept helps in determining how electrons are distributed across a molecule.
Consider these points when arranging bonds by polarity:

• If the electronegativity difference is high, the bond is highly polar. A classic example is the hydrogen-fluoride (HF) bond.
• If the electronegativity difference is very low, the bond tends to be nonpolar, like the bond between two carbon atoms (C-C).

In exercises involving polarity order, calculating the electronegativity differences first is key. Let's say we are evaluating bonds like C-F and Be-F from the exercise, you calculate: - Be-F has a higher electronegativity difference compared to C-F, making it more polar.
The sequence you're looking for with increasing polarity in such problems typically starts with the least difference in electronegativity, moving to the greatest. This organized arrangement helps understand which bonds have more "electron attraction inequality," leading to predictions about molecular properties like solubility and boiling points.