Question

Identify the most important types of interparticle forces present in the solids of each of the following substances. a. Ar e. \(\mathrm{CH}_{4}\) b. \(\mathrm{HCl}\) f. \(\mathrm{CO}\) c. HF g. \(\mathrm{NaNO}_{3}\) d. \(\mathrm{CaCl}_{2}\)

Short answer

a. Ar: London dispersion forces e. \(\mathrm{CH}_{4}\): London dispersion forces b. \(\mathrm{HCl}\): Dipole-dipole attractions f. \(\mathrm{CO}\): Dipole-dipole attractions c. HF: Hydrogen bonds g. \(\mathrm{NaNO}_{3}\): Ionic bonds d. \(\mathrm{CaCl}_{2}\): Ionic bonds

Step-by-step solution

Identify the Type of Bonding for Each Substance

To identify the most important type of interparticle force, we need to first evaluate the type of bonding present in each substance. a. Ar: Noble gas - Van der Waals forces (specifically, London dispersion forces) e. \(\mathrm{CH}_{4}\): Non-polar covalent molecules - Van der Waals forces (specifically, London dispersion forces) b. \(\mathrm{HCl}\): Polar covalent molecules - Van der Waals forces (specifically, dipole-dipole attractions) f. \(\mathrm{CO}\): Polar covalent molecules - Van der Waals forces (specifically, dipole-dipole attractions) c. HF: Polar covalent molecules with hydrogen bond donor and acceptor - Hydrogen bonds g. \(\mathrm{NaNO}_{3}\): Ionic compound - Ionic bonds d. \(\mathrm{CaCl}_{2}\): Ionic compound - Ionic bonds

Summarize the Most Important Type of Interparticle Forces for Each Substance

Based on the bonding identified in each substance, we can now list the most important type of interparticle forces present in their solid forms. a. Ar: London dispersion forces e. \(\mathrm{CH}_{4}\): London dispersion forces b. \(\mathrm{HCl}\): Dipole-dipole attractions f. \(\mathrm{CO}\): Dipole-dipole attractions c. HF: Hydrogen bonds g. \(\mathrm{NaNO}_{3}\): Ionic bonds d. \(\mathrm{CaCl}_{2}\): Ionic bonds

Key concepts

London dispersion forces

London dispersion forces are the weakest type of intermolecular force, yet they are fundamental in nature. They arise due to the temporary fluctuations in electron density in atoms and molecules. This creates temporary dipoles, leading to attractions between molecules.

All molecules and atoms exhibit London dispersion forces, regardless of whether they are polar or nonpolar. These forces are particularly significant in noble gases like argon (Ar) and non-polar molecules like methane (\(\mathrm{CH}_{4}\)).

Why London Dispersion Forces Matter:

• They allow non-polar substances to condense into liquids and solids.
• They explain why substances like argon can exist in a solid state at very low temperatures.

Dipole-dipole attractions

Dipole-dipole attractions occur in polar molecules where there is a significant difference in electronegativity between atoms. This results in one part of the molecule being more negatively charged, while another becomes positively charged.

These attractions are stronger than London dispersion forces because they involve permanent dipoles aligning themselves.

Examples of Dipole-Dipole Attractions:

• \(\mathrm{HCl}\) (Hydrogen Chloride): A classic example where the bond between hydrogen and chlorine results in a permanent dipole.
• \(\mathrm{CO}\) (Carbon Monoxide): Exhibits dipole-dipole interactions due to the polar covalent bond between carbon and oxygen.

Hydrogen bonds

Hydrogen bonds are a special type of dipole-dipole attraction. They occur when hydrogen is directly bonded to a highly electronegative atom such as nitrogen, oxygen, or fluorine.

These bonds are stronger than regular dipole-dipole interactions due to the significant difference in electronegativity and the small size of hydrogen, which allows for close approach.

The Role of Hydrogen Bonds:

• They are crucial in biological systems, influencing the structure of DNA and proteins.
• \(\mathrm{HF}\) (Hydrogen Fluoride): Exhibits hydrogen bonding, making it much more cohesive and influencing its boiling point.

Ionic bonds

Ionic bonds are a strong type of chemical bonding that arises from the electrostatic attraction between oppositely charged ions.

These bonds form when electrons are transferred from one atom to another, usually between metals and nonmetals.

Characteristics of Ionic Bonds:

• They result in the formation of solid crystalline structures like table salt (NaCl).
• \(\mathrm{NaNO}_{3}\) (Sodium Nitrate) and \(\mathrm{CaCl}_{2}\) (Calcium Chloride) are examples of compounds held together by ionic bonds, leading to high melting points.

Polar covalent molecules

Polar covalent molecules are formed when atoms with different electronegativities share electrons unequally. This results in one atom having a partial negative charge and the other a partial positive charge.

Polar covalent bonds occur in molecules such as water, where oxygen attracts the shared electrons more than hydrogen does, creating a dipole.

Importance of Polar Covalent Molecules:

• They exhibit dipole-dipole interactions, contributing to their liquid or solid states in certain conditions.
• They are essential in many chemical reactions and their understanding helps in predicting the behavior of substances like \(\mathrm{HCl}\) and \(\mathrm{CO}\).