Properties of Solids, Liquids & Gases (College Board AP® Chemistry): Flashcards

Ionic solids are brittle because applying stress shifts the lattice so that like-charged ions align, causing repulsion.

Ionic bond strength increases as ion charges increase in magnitude (greater electrostatic attraction) and as ions get smaller (shorter interionic distance). Both factors raise the melting point of the ionic solid.

False.

Ionic solids are brittle. When a layer shifts, like charges align and repel each other, shattering the lattice. Malleability is a property of metallic solids, not ionic solids.

A solid in which atoms are held together throughout by an extended network of covalent bonds, giving very high hardness and melting points compared to molecular solids.

Each carbon atom in diamond forms four strong covalent bonds arranged tetrahedrally to four neighbouring carbons. This rigid, three-dimensional network resists deformation in all directions, making diamond extremely hard.

False.

All valence electrons in diamond are involved in covalent bonds and there are no mobile charge carriers. Diamond is a poor conductor of electricity, though it conducts heat well.

In graphite, each carbon atom bonded in a planar hexagonal ring has one electron not used in bonding. These electrons are delocalized across the layers, enabling electrical conduction.

Graphite layers of hexagonal carbon rings are held to one another only by weak London dispersion forces. These weak interlayer forces allow the layers to slide past each other easily, providing lubrication.

In SiO₂ each silicon bonds to four oxygens and each oxygen bonds to two silicons, forming a tetrahedral network with two element types. Diamond bonds only C to C. Both share high hardness and high melting point because all valence electrons are locked in strong covalent bonds throughout the network.

False.

Pure silicon carbide is an insulator — there are no free electrons to carry charge. Semiconductor behavior only appears when impurities are intentionally added.

1. Cutting tools and bearings — hardness close to diamond, from its strong tetrahedral Si–C covalent bonds.\n\n1. Fire bricks and heat-resistant materials — high temperature resistivity and low thermal expansion from the strong Si–C bonds.

A solid of neutral molecules held together by intermolecular forces rather than ionic or covalent network bonds.

False.

Molecular solids do not conduct electricity because their valence electrons are tied up in intramolecular covalent bonds and are not free to move through the solid.

Both rely on London dispersion forces, but iodine molecules are larger with more electrons, increasing polarizability. Stronger intermolecular forces require more energy to overcome, raising the melting point.

Molecular solids with permanent dipole moments generally melt at higher temperatures than nonpolar molecular solids of similar molar mass.

Molecular solids are held together only by weak intermolecular forces between neutral molecules. Covalent network solids are held by strong covalent bonds extending throughout the entire structure, requiring far more energy to disrupt.

The electrostatic attraction between a lattice of positive metal ions and a surrounding sea of delocalized valence electrons that are free to move throughout the solid.

Metallic solids contain delocalized valence electrons that are free to move throughout the metal lattice. These mobile electrons carry charge under an applied potential difference, enabling conduction.

True.

The delocalized electron sea moves with the shifting ion layers, maintaining attraction throughout. Unlike ionic solids, no like-charge repulsion develops when layers shift, so metallic solids deform rather than fracture.

In a substitutional alloy, solute atoms replace solvent atoms in the lattice when they have similar atomic radii and bonding characteristics.

Steel is an interstitial alloy: small carbon atoms occupy holes between iron atoms and form covalent bonds to neighboring iron atoms. This makes the lattice harder, stronger, and less malleable than pure iron, while electrical conductivity is retained because delocalized electrons are unaffected.

False.

Delocalized electrons responsible for conduction are retained in the alloy. Interstitial atoms change mechanical properties (hardness, strength) but do not significantly impair electrical conductivity.

In a substitutional alloy, solute atoms of similar size replace solvent atoms at lattice positions (e.g., brass: zinc in copper). In an interstitial alloy, smaller solute atoms fill gaps between solvent atoms (e.g., steel: carbon in iron).

Noncovalent interactions between nonpolar groups and polar solvent molecules such as water, where the nonpolar groups cluster together to minimize contact with the polar solvent. This explains why large nonpolar biomolecules such as oils do not dissolve in water.

1. Hydrogen bonding (O-H or N-H with electronegative atoms N, O, F)

1. Electrostatic/ionic interactions (between permanent dipoles or charged groups)

1. Hydrophobic interactions (nonpolar regions avoiding water)

1. Van der Waals interactions (dipole-dipole and London dispersion forces)

True.

Hydrogen bonds form between a polar H on an O-H or N-H bond and the lone electron pairs of highly electronegative atoms such as nitrogen, oxygen, or fluorine.

Large biological molecules such as starch and cellulose are called polymers, and they are built from smaller units called monomers.

Large biomolecules such as proteins contain many noncovalent interactions (hydrogen bonds, electrostatic interactions, hydrophobic interactions and van der Waals forces) that collectively stabilize three-dimensional structures and govern biological function, including interactions with nutrients such as phenolic compounds in food.

True.

Van der Waals interactions include dipole-dipole forces (between polar molecules with permanent dipoles) and London dispersion forces (between nonpolar molecules with induced dipoles). Both types are classified as van der Waals interactions.

A solid in which atoms, ions, or molecules are arranged in an orderly, repeating three-dimensional pattern (crystal lattice) that maximizes the net attractive intermolecular forces between particles.

False.

Amorphous solids have a disordered structure similar to liquids at the atomic level. Particles lack the orderly repeating arrangement of crystalline solids, often because the liquid cooled too quickly to allow crystallization.

Crystalline solids can be held together by ionic forces, covalent bonds, van der Waals forces, hydrogen bonds or a combination of these forces, depending on the nature of the constituent particles.

In crystalline solids, particles are arranged so that the net attractive intermolecular forces are at their maximum.

Amorphous solids form when liquids cool too quickly for molecules to arrange into an ordered pattern. At the atomic level their structure is disordered and resembles that of a liquid, but particles lack the freedom of motion they have in liquids.

Crystalline: sodium chloride and diamond (ordered repeating lattice structures).

Amorphous: glass and rubber (disordered atomic arrangements, formed by rapid cooling or polymer entanglement).

A measure of a liquid's resistance to flow. Viscosity increases with stronger intermolecular forces between particles and decreases as temperature increases.

Stronger intermolecular forces reduce vapor pressure because molecules are more strongly held in the liquid phase. Increasing temperature raises vapor pressure because more molecules gain enough energy to escape into the vapor phase.

True.

Unlike gases, particles in a liquid are closely packed with minimal empty space between them. Compressing a liquid would require forcing particles closer together against their repulsive forces, which demands extremely high pressures.

Surface tension — the energy required to increase the surface area of a liquid — increases with increasing strength of intermolecular force.

Molar volume depends on the spacing between particles. In both the solid and liquid phases, particles are in close contact with approximately the same interparticle distance, so the volume occupied by one mole is nearly the same in both phases.

False.

Data for metals such as silver, aluminum and copper show that molar volumes in the liquid state are only slightly larger than in the solid state (e.g., Ag: 10.3 cm³/mol solid vs 10.7 cm³/mol liquid). The small difference reflects only a slight increase in interparticle spacing on melting.

A model that explains the behavior of gases by describing gas particles as being in constant random motion with negligible intermolecular forces, where temperature measures average kinetic energy and pressure results from particle collisions with container walls.

Temperature is an indicator of the average kinetic energy of the gas particles. An increase in temperature corresponds to an increase in average kinetic energy and an increase in molecular motion.

False.

Gas particles have very little intermolecular force between them and are in constant random motion. Because particles are not held together, gases have neither fixed volume nor fixed shape, and are highly compressible.

The pressure of a gas is determined by how often and how forcefully gas particles strike the walls of its container.

Gas particles have negligible intermolecular forces and are widely spaced, so pressure, volume, temperature and molar amount are simply related by the ideal gas equation. In liquids and solids, significant intermolecular forces and close particle packing make such a simple universal relationship impossible.

1. No fixed volume or shape (particles in constant random motion with negligible intermolecular forces)

1. Highly compressible (large distances between particles provide space to compress into)

1. Much lower density than liquids or solids (particles are widely spaced)