Intermolecular Forces, Liquids, and Solids Flashcards

Comprehensive practice flashcards covering Chapter 11 material on intermolecular forces, properties of liquids, phase changes, unit cells, and types of crystalline solids.

What two competing energies determine the physical state of a given substance?

The kinetic energy of the particles and the interparticle energies of attraction.

Based on the provided diagram of phase transitions, what two physical processes can convert a gas into a liquid state?

Cooling or compressing the gas.

How strong are intermolecular forces compared to intramolecular ionic or covalent bonds?

Intermolecular forces are much weaker, being less than $15\%$ as strong as intramolecular bonds.

What is polarizability, and how is it affected by molecular size?

Polarizability is the ease with which the charge distribution or electron cloud in a molecule can be distorted by an external electric field. Larger molecules with more electrons have greater polarizability and stronger London dispersion forces.

What structural features are required for a substance to exhibit hydrogen bonding?

A hydrogen atom covalently bonded to a small, highly electronegative atom ($F$, $O$, or $N$) and an unshared electron pair on a nearby electronegative atom ($F$, $O$, or $N$).

Why is solid ice less dense than liquid water?

Water molecules in ice form an open, regular hexagonal structure to optimize hydrogen bonding, with an $H-O$ bond length of $1.0\,\text{\AA}$ and an $O\cdots H$ hydrogen bond length of $1.8\,\text{\AA}$.

How do cohesive forces differ from adhesive forces in liquids?

Cohesive forces are intermolecular forces that bind like molecules to one another, whereas adhesive forces bind molecules to a surface or container.

Why does water form a concave (U-shaped) meniscus in a glass tube while mercury forms a convex (downward-curved) meniscus?

Water has stronger adhesive forces to glass than cohesive forces among water molecules, while mercury has stronger cohesive forces between its atoms than adhesive forces to glass.

Why is the enthalpy of vaporization ($\Delta H_{vap}$) for a liquid generally much larger than its enthalpy of fusion ($\Delta H_{fus}$)?

Vaporization requires completely separating molecules against their intermolecular forces, whereas melting only requires partially breaking or disrupting the ordered structure.

What are the definitions of critical temperature and critical pressure?

Critical temperature is the highest temperature at which a substance can exist as a liquid, and critical pressure is the pressure required to liquefy a substance at its critical temperature.

What linear equation relates vapor pressure to temperature, and what does its slope represent on a plot of $\ln(P)$ vs $\frac{1}{T}$?

The Clausius-Clapeyron equation, $\ln(P) = -\frac{\Delta H_{vap}}{RT} + \text{Constant}$, where the slope of the plot equals -$\frac{\Delta H_{vap}}{R}$.

What is the triple point on a phase diagram?

The unique combination of temperature and pressure at which all three phases (solid, liquid, and gas) exist simultaneously in dynamic equilibrium.

What are the net number of atoms contained in a primitive cubic, a body-centered cubic (bcc), and a face-centered cubic (fcc) unit cell?

A primitive cubic cell has $1$ net atom, a body-centered cubic cell has $2$ net atoms, and a face-centered cubic cell has $4$ net atoms.

How many net $Na^+$ and $Cl^-$ ions are present in a single unit cell of sodium chloride ($NaCl$)?

There are $4$ net $Na^+$ ions ($(\frac{1}{4} \times 12\,\text{edges}) + 1\,\text{center} = 4$) and $4$ net $Cl^-$ ions ($(\frac{1}{8} \times 8\,\text{corners}) + (\frac{1}{2} \times 6\,\text{faces}) = 4$).

Based on Table 11.7, what are the unit particles, forces between particles, properties, and examples of covalent-network solids?

Unit particles: atoms connected in a network of covalent bonds; Forces: covalent bonds; Properties: very hard, very high melting point, often poor thermal and electrical conduction; Examples: diamond ($C$), quartz ($SiO_2$).

What is the coordination number of a central sphere in close-packed structures such as hexagonal close packing (hcp) and cubic close packing (ccp)?

The coordination number is $12$.

What is the difference between a substitutional alloy and an interstitial alloy?

A substitutional alloy forms when host metal atoms are replaced by other metal atoms of similar size (e.g., brass), whereas an interstitial alloy forms when smaller atoms fill the interstitial spaces between host metal atoms in the lattice (e.g., steel).