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

Short answer

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

Step-by-step solution

Identify Electronegativity Values

Find out the electronegativity values of the involved elements. You can use a Periodic Table to get the values. Remember that electronegativity generally increases from left to right and decreases top to bottom in the periodic table.

Calculate Electronegativity Differences

For each bond, find the absolute difference in electronegativity values between the two bonding elements. This value will be used to determine bond polarity.

Arrange Bonds in Order of Increasing Polarity

Compare the electronegativity differences calculated in Step 2, and arrange the bonds in each set in order of increasing polarity. This method can be applied to arrange the bond sets provided in the exercise as shown below: (a) \(\mathrm{C}-\mathrm{F}, \mathrm{O}-\mathrm{F}, \mathrm{Be}-\mathrm{F}\) Electronegativity values: C (2.55), F (3.98), O (3.44), Be (1.57) Electronegativity differences: \(\mathrm{C}-\mathrm{F}: |3.98 - 2.55| = 1.43\) \(\mathrm{O}-\mathrm{F}: |3.98 - 3.44| = 0.54\) \(\mathrm{Be}-\mathrm{F}: |3.98 - 1.57| = 2.41\) Arranged by increasing polarity: \(\mathrm{O}-\mathrm{F} < \mathrm{C}-\mathrm{F} < \mathrm{Be}-\mathrm{F}\) (b) \(\mathrm{O}-\mathrm{Cl}, \mathrm{S}-\mathrm{Br}, \mathrm{C}-\mathrm{P}\) Electronegativity values: O (3.44), Cl (3.16), S (2.58), Br (2.96), C (2.55), P (2.19) Electronegativity differences: \(\mathrm{O}-\mathrm{Cl}: |3.44 - 3.16| = 0.28\) \(\mathrm{S}-\mathrm{Br}: |2.58 - 2.96| = 0.38\) \(\mathrm{C}-\mathrm{P}: |2.55 - 2.19| = 0.36\) Arranged by increasing polarity: \(\mathrm{O}-\mathrm{Cl} < \mathrm{C}-\mathrm{P} < \mathrm{S}-\mathrm{Br}\) (c) \(\mathrm{C}-\mathrm{S}, \mathrm{B}-\mathrm{F}, \mathrm{N}-\mathrm{O}\) Electronegativity values: C (2.55), S (2.58), B (2.04), F (3.98), N (3.04), O (3.44) Electronegativity differences: \(\mathrm{C}-\mathrm{S}: |2.55 - 2.58| = 0.03\) \(\mathrm{B}-\mathrm{F}: |3.98 - 2.04| = 1.94\) \(\mathrm{N}-\mathrm{O}: |3.44 - 3.04| = 0.4\) Arranged by increasing polarity: \(\mathrm{C}-\mathrm{S} < \mathrm{N}-\mathrm{O} < \mathrm{B}-\mathrm{F}\)

Key concepts

Periodic Table

The Periodic Table is a fundamental tool in chemistry that organizes elements according to their chemical properties. It is arranged in a grid format, with rows called periods and columns known as groups. Understanding the layout of the Periodic Table helps in predicting and explaining the behavior of elements during chemical reactions. The elements are ordered by increasing atomic number, which represents the number of protons in an atom's nucleus. As you move from left to right across a period, the atomic number increases, and elements exhibit a gradual increase in electronegativity. Electronegativity is the ability of an atom to attract electrons in a chemical bond. Within a group or column, electronegativity typically decreases as you move down the Periodic Table because the outermost electrons are further from the nucleus.

Chemical Bonds

Chemical bonds are the connections formed between atoms in molecules. They involve the sharing or transfer of electrons to achieve stable electron configurations. The three primary types of chemical bonds are:

• Ionic Bonds: These occur when electrons are transferred from one atom to another, resulting in oppositely charged ions that attract each other. Typically found between metals and non-metals, they have large differences in electronegativity.
• Covalent Bonds: In these bonds, atoms share electrons to achieve stability. They can be polar or non-polar, depending on the electronegativity difference between the involved atoms.
• Metallic Bonds: Found in metals, these involve a "sea of electrons" that move freely, allowing metals to conduct electricity and heat well.

Electronegativity plays a key role in determining the type and polarity of a bond, with larger differences resulting in more polar (or even ionic) bonds.

Polarity

Polarity in chemistry refers to the distribution of electrical charge over the atoms involved in a bond. It's influenced by the difference in electronegativity between two bonded atoms. In a polar covalent bond, the atom with higher electronegativity attracts the shared electrons more strongly, creating a partial negative charge, while the less electronegative atom becomes partially positive. This within a molecule leads to a dipole moment, with one end being more negatively charged than the other. Here are some key points about polarity:

• Non-polar Covalent Bonds: These occur when atoms share electrons fairly equally, usually between the same element or those with minimal electronegativity differences.
• Polar Covalent Bonds: Results from a significant, but not extreme, electronegativity difference, creating a partial charge separation.
• Importance of Molecular Shape: The overall polarity of a molecule can also be affected by its shape, as symmetrical molecules might have non-polar characteristics even if they contain polar bonds.

Polarity is crucial in determining the physical properties of substances, such as solubility, boiling point, and melting point.

Electronegativity Differences

The concept of electronegativity differences is central to predicting the type and strength of chemical bonds formed between elements. When two atoms form a bond, their electronegativity values influence how electrons are shared or transferred:

• Small Difference: Suggests a non-polar covalent bond where electrons are shared relatively equally.
• Moderate Difference: Leads to polar covalent bonds, where electrons are unequally shared, resulting in partial charges.
• Large Difference: Often results in ionic bonds, where one atom essentially "takes" electrons from the other, creating ions.

The bond polarity depends directly on these electronegativity differences. For instance, the bond in a \( \mathrm{C}-\mathrm{F} \), with a high difference, is more polar water while a bond like \( \mathrm{O}-\mathrm{F} \), with a smaller difference, is less polar. Quantitatively, larger electronegativity differences equate to strong polar bonds or ionic character.