Problem 16 - Chemistry: The Central Science in SI Units, Global Edition

Question

(a) Which is generally stronger, intermolecular interactions or intramolecular interactions? (b) Which of these kinds of interactions are broken when a liquid is converted to a gas?

Step-by-Step Solution

Answer

(a) Intramolecular interactions are generally stronger than intermolecular interactions. (b) Intermolecular interactions are broken when a liquid is converted to a gas during the process of vaporization.

Step 1: Part (a): Understanding intermolecular and intramolecular interactions

Intermolecular interactions are the forces of attraction or repulsion between particles (atoms, molecules, or ions) in a substance. Some examples of intermolecular forces include hydrogen bonding, dipole-dipole interactions, and van der Waals forces. Intramolecular interactions, on the other hand, are the forces that hold atoms together within a molecule. These forces are chemical bonds, such as covalent bonds, ionic bonds, and metallic bonds.

Step 2: Part (a): Identifying the stronger type of interaction

Generally, intramolecular interactions are stronger than intermolecular interactions. This is because chemical bonds, which are within molecules, have more energy and are more difficult to break than the forces of attraction or repulsion between particles in a substance.

Step 3: Part (b): Understanding the process of liquid to gas conversion

When a liquid is converted to a gas, a substance undergoes a change of state called vaporization. During vaporization, particles in the liquid phase gain enough energy to overcome the forces of attraction between them, allowing them to move freely and become part of the gas phase.

Step 4: Part (b): Identifying the type of interactions broken during vaporization

Vaporization involves breaking the intermolecular interactions between particles in a substance, as these are the forces that hold them together in the liquid phase. The intramolecular interactions within molecules usually remain intact during this process, as they are stronger and involve more energy.

Key Concepts

Intramolecular Interactions

Intramolecular interactions are the forces that keep the atoms in a molecule tightly bound together. These interactions form the foundation of molecular structure. Intramolecular forces are generally strong because they involve chemical bonds like covalent, ionic, and metallic bonds.

• Covalent bonds occur when two atoms share electrons, forming a stable balance of attractive and repulsive forces.
• Ionic bonds are formed when one atom donates electrons to another, creating positively and negatively charged ions that attract each other.
• Metallic bonds involve the sharing of free electrons among a lattice of metal atoms.

These bonds require significantly more energy to break compared to intermolecular forces. That's why intramolecular interactions are generally stronger than intermolecular interactions. This intrinsic strength is what gives molecules their specific shapes and chemical properties.

Vaporization

Vaporization refers to the transformation of a substance from a liquid to a gas. This process involves breaking the intermolecular forces that keep the molecules in the liquid phase together. In the liquid state, molecules are closely packed but still have the ability to move around. When heat energy is introduced:

• It provides molecules with enough kinetic energy to overcome the attractions holding them in the liquid form.
• As a result, molecules escape into the gas phase, where they are more freely dispersed.

It's important to remember that during vaporization, only intermolecular interactions are broken, not the intramolecular bonds within the molecules themselves. The strength and type of intermolecular forces present in a liquid affect the amount of energy required for vaporization—polar liquids with strong hydrogen bonds for example, need more energy to become a gas than non-polar liquids with weaker van der Waals forces.

Chemical Bonds

Chemical bonds are the fundamental connections between atoms that build molecules and compounds. They are a result of the interactions of electrons that hold atoms together in a stable arrangement. Several types of chemical bonds include:

• Covalent bonds - Formed by the sharing of electron pairs between atoms, creating a balance between attractive and repulsive forces.
• Ionic bonds - Occur when electrons are transferred from one atom to another, resulting in attraction between positive and negative ions.
• Metallic bonds - Found in metals, these involve a sea of shared electrons flowing freely and holding metal atoms together.

Chemical bonds determine the molecule's structural stability and influence its physical properties such as boiling and melting points, solubility, and electrical conductivity. Understanding these bonds is crucial for grasping how molecules function and react in various environments.