Question

Which forces are intramolecular and which intermolecular? (a) Those preventing oil from evaporating at room temperature (b) Those preventing butter from melting in a refrigerator (c) Those allowing silver to tarnish (d) Those preventing \(\mathrm{O}_{2}\) in air from forming \(\mathrm{O}\) atoms

Short answer

Intermolecular: (a), (b). Intramolecular: (c), (d).

Step-by-step solution

Identify intermolecular and intramolecular forces

To distinguish between intramolecular and intermolecular forces, remember: intramolecular forces are the forces within a molecule that keep the atoms together (e.g., covalent bonds), while intermolecular forces are the forces between molecules (e.g., hydrogen bonds, Van der Waals forces).

- Preventing oil from evaporating

The forces preventing oil from evaporating are intermolecular forces. These include Van der Waals forces which act between the oil molecules to hold them together in the liquid phase.

- Preventing butter from melting

The forces preventing butter from melting in a refrigerator are also intermolecular forces. These include hydrogen bonds and Van der Waals forces that keep the butter solid at low temperatures.

- Allowing silver to tarnish

The forces allowing silver to tarnish involve intramolecular forces. The tarnishing process forms a new compound on the silver surface through chemical bonds (intramolecular forces) between silver atoms and sulfur atoms from the environment.

- Preventing \(\text{O}_{2}\) from forming \(\text{O}\) atoms

The forces preventing \(\text{O}_{2}\) in the air from forming \(\text{O}\) atoms are intramolecular forces. These forces are the covalent bonds that hold the two oxygen atoms together in a \(\text{O}_{2}\) molecule.

Key concepts

Van der Waals forces

Van der Waals forces are a type of intermolecular force. They are the weakest of all intermolecular attractions but are crucial for the physical properties of molecules. These forces come from temporary dipoles occurring in molecules due to momentary imbalances in electron distribution.
Van der Waals forces include:

• London dispersion forces
• Dipole-dipole interactions

For instance, they are the forces that prevent oil from evaporating at room temperature, keeping the oil molecules together in the liquid phase. While weak, they play an essential role in the states and behaviors of molecular substances.

Hydrogen bonds

Hydrogen bonds are a special type of dipole-dipole interaction and are stronger than Van der Waals forces but weaker than covalent bonds. These bonds occur when hydrogen is covalently bonded to a highly electronegative atom, such as oxygen, nitrogen, or fluorine. The hydrogen atom then interacts with another electronegative atom nearby.
Hydrogen bonds provide a different set of characteristics:

• High boiling and melting points for water
• Maintaining the structure of DNA through base pairing
• Stabilizing protein structures

For example, the hydrogen bonds in butter help in preventing it from melting quickly when refrigerated, maintaining its solid state at lower temperatures. These interactions are vital for many biological and chemical processes.

Covalent bonds

Covalent bonds are a type of intramolecular force, formed when two atoms share electrons. These bonds are strong and responsible for holding atoms together within a molecule. Covalent bonds are fundamental to the structural integrity of most organic molecules.
Key characteristics of covalent bonds include:

• Providing stability to complex molecules like proteins and nucleic acids
• Requiring significant energy to break
• Determining the molecular structure

For instance, in the case of preventing \( \text{O}_{2} \) from forming \( \text{O} \) atoms, the strong covalent bonds between oxygen atoms maintain the molecular integrity of \( \text{O}_{2} \). Additionally, the formation of tarnish on silver involves the creation of new covalent bonds between the silver surface and sulfur from the environment.