The ease with which an atom's or molecule's electron cloud can be distorted to form a temporary dipole is called polarizability.
Missing Word
polarizability
Polarizability measures how easily an electron cloud is distorted. Larger atoms and molecules, whose outer electrons are farther from the nucleus, are more polarizable and therefore have stronger dispersion forces.
Category: Intermolecular Forces
Question 2
Attractions between the partially positive end of one polar molecule and the partially negative end of another are called dipole-dipole attractions.
Missing Word
dipole-dipole
Dipole-dipole attractions act between polar molecules, which have permanent partial charges. They are stronger than dispersion forces between molecules of similar size, so polar compounds tend to boil at higher temperatures than comparable nonpolar ones.
Category: Intermolecular Forces
Question 3
The attraction between molecules of a liquid and molecules of a different substance, such as the glass of a tube, is called adhesion.
Missing Word
adhesion
Adhesion is the attraction between unlike substances. It is what draws water up the walls of a glass tube in capillary action.
Category: Properties of Liquids
Question 4
The attraction between molecules of the same substance, which pulls a drop of water into a rounded bead, is called cohesion.
Missing Word
cohesion
Cohesion is the attraction among molecules of one substance. Strong cohesion in water gives it a high surface tension, letting drops bead up on a waxed surface.
Category: Properties of Liquids
Question 5
The curved upper surface of a liquid in a narrow tube, such as water in a graduated cylinder, is called a meniscus.
Missing Word
meniscus
A meniscus forms because of the balance between cohesive and adhesive forces. Water forms a concave meniscus in glass, so volumes are read at the bottom of the curve.
Category: Properties of Liquids
Question 6
The direct change of a solid into a gas, as when dry ice disappears without leaving a puddle, is called sublimation.
Missing Word
sublimation
Sublimation is the phase change from solid straight to gas without passing through the liquid state. It is endothermic, and its reverse is deposition.
Category: Phase Transitions
Question 7
Melting, the change of a solid into a liquid, is also known as fusion.
Missing Word
fusion
Fusion is another name for melting. The heat absorbed per mole as a solid melts at its melting point is called the enthalpy of fusion.
Category: Phase Transitions
Question 8
Melting 3 mol of ice at 0 degrees Celsius, which requires 6.0 kJ per mole, absorbs 18 kJ of heat.
Missing Word
18
The heat for a phase change equals moles times the molar enthalpy of the change: 3 mol x 6.0 kJ/mol = 18 kJ. The temperature stays at 0 degrees Celsius until all the ice has melted.
Category: Phase Transitions
Question 9
A liquid that evaporates readily at room temperature because of its high vapor pressure is described as volatile.
Missing Word
volatile
A volatile liquid has weak intermolecular forces, so many molecules escape from its surface even at room temperature. Acetone and diethyl ether are common examples.
Category: Phase Transitions
Question 10
A solid whose particles are arranged in a regular, repeating three-dimensional pattern is called crystalline.
Missing Word
crystalline
A crystalline solid has long-range order, so it has flat faces, definite angles and a sharp melting point. Solids that lack this order, such as glass, are amorphous.
Category: Types of Solids
Question 11
Diamond and graphite are both covalent network solids made entirely of the element carbon.
Missing Word
carbon
Diamond and graphite are two forms of carbon with different bonding arrangements. In diamond each atom bonds to four others in three dimensions, while graphite consists of stacked sheets of atoms.
Category: Types of Solids
Question 12
In a face-centered cubic structure, each atom has 12 nearest neighbors.
Missing Word
12
The coordination number of a face-centered cubic structure is 12: four neighbors in its own layer plane, four above and four below. It is one of the two closest ways to pack identical spheres, along with hexagonal closest packing.
Category: Crystal Lattices
Question 13
Each atom in a simple cubic lattice has a coordination number of 6, with neighbors directly above, below and on four sides.
Missing Word
6
In a simple cubic lattice, each atom touches one neighbor in each direction along the three axes, for a coordination number of 6. This is the least efficient of the cubic packings.
Category: Crystal Lattices
Question 14
A body-centered cubic unit cell contains a net of 2 atoms: one at the center plus one-eighth of each of the eight corner atoms.
Missing Word
2
The center atom belongs entirely to the cell, and the eight corner atoms contribute 8 x 1/8 = 1 atom, so the total is 2. Iron and chromium crystallize in this structure at room temperature.
Category: Crystal Lattices
Question 15
The equation n lambda = 2d sin theta, used to find the spacing between planes of atoms from X-ray diffraction, is named for the father-and-son team of William Henry and William Lawrence Bragg.
Missing Word
Bragg
The Bragg equation relates X-ray wavelength, diffraction angle and the distance between layers of atoms in a crystal. It lets chemists work out crystal structures and unit cell dimensions.
Category: Crystal Lattices