Question

Arrange the following bonds in order of increasing polarity. (a) \(\mathrm{O}-\mathrm{H}, \mathrm{C}-\mathrm{H}, \mathrm{H}-\mathrm{H}, \mathrm{F}-\mathrm{H}\) (b) \(\mathrm{O}-\mathrm{Cl}, \mathrm{C}-\mathrm{Cl}, \mathrm{H}-\mathrm{Cl}, \mathrm{F}-\mathrm{Cl}\)

Short answer

In increasing order of polarity, the bonds from part (a) are H-H, C-H, O-H, and F-H. For part (b), the increasing order of polarity is O-Cl, F-Cl, C-Cl, and H-Cl.

Step-by-step solution

Understanding Electronegativity

Electronegativity is a measure of an atom's ability to attract shared electrons towards itself. The higher the electronegativity of an element, the greater its power to pull electrons towards it.

Arranging bonds from part (a)

Reference electronegativity values: Hydrogen (H) - 2.1, Carbon (C) - 2.55, Oxygen (O) - 3.44, and Fluorine (F) - 3.98. Remembering that increasing polarity is determined by increasing difference in electronegativity, the bonds can be ordered as follows: H-H (difference = 0), C-H (difference = 0.45), O-H (difference = 1.34), and F-H (difference = 1.88).

Arranging bonds from part (b)

Reference electronegativity values: Chlorine (Cl) - 3.16. Using the same approach as in step 2: H-Cl (difference = 1.06), C-Cl (difference = 0.61), O-Cl (difference = 0.28), and F-Cl (difference = 0.82).

Key concepts

Electronegativity

Electronegativity is a fundamental concept in chemistry that describes an atom's tendency to attract and hold onto electrons in a chemical bond. Each element has a specific electronegativity value, which helps determine how it will interact with other elements.

• The higher the electronegativity, the greater the atom's ability to attract electrons.
• Fluorine is the most electronegative element, with a value of 3.98 on the Pauling scale, giving it a strong pull on electrons.
• Hydrogen has a lower electronegativity value of 2.1, indicating a weaker electron-attracting ability compared to elements like oxygen or chlorine.

Understanding electronegativity is crucial for predicting bond types and molecular behaviors. The difference in electronegativity values between two atoms can influence the bond's polarity, one of the core factors determining how molecules interact with each other physically and chemically.

Chemical Bonds

Chemical bonds are the glue that holds atoms together within a molecule. There are several types of chemical bonds, but the key focus here is on polar and nonpolar covalent bonds. The type and polarity of these bonds depend significantly on electronegativity.

• Nonpolar covalent bonds occur when two atoms have equal or very similar electronegativity values, leading to an equal sharing of electrons, like in the hydrogen-hydrogen (H-H) bond.
• Polar covalent bonds occur when there is a noticeable difference in electronegativity between the two atoms, resulting in unequal sharing of electrons. This causes one atom to develop a partial negative charge, and the other a partial positive charge.
• Examples include the oxygen-hydrogen (O-H) and fluorine-hydrogen (F-H) bonds, where oxygen and fluorine pull more strongly on the shared electrons than hydrogen does.

Understanding the types of chemical bonds and their polarity helps in predicting molecule behavior and interactions, influencing how substances mix and engage with each other.

Molecular Polarity

Molecular polarity is an extension of the concept of bond polarity, determining how molecules interact on a larger scale. While bond polarity looks at individual bonds, molecular polarity considers the whole shape and structure of a molecule.

• A molecule is nonpolar if it has nonpolar bonds or if its polar bonds are symmetrically arranged, canceling out the dipole moments. Carbon dioxide (CO₂) is an example of a nonpolar molecule despite having polar bonds.
• A molecule is polar if it contains polar bonds that don't offset each other, resulting in a net dipole moment. Water (H₂O), with its bent shape and polar O-H bonds, is a classic example of a polar molecule.
• Molecular polarity affects properties like boiling and melting points, solubility, and intermolecular interactions. Polar molecules, for example, tend to dissolve well in polar solvents, adhering to the "like dissolves like" principle.

Grasping the concept of molecular polarity allows for a better understanding of molecular behavior and the properties of various substances, crucial for applications ranging from biology to industrial chemistry.