Chem Ch. 12

The structure of compounds in their crystalline states can be determined by using ___ ray diffraction a. gamma b. delta c. X

C

The individual shapes of the lattice, then, form..

"tiles," or unit cells, that must fill the entire space of the substance.

Determine the packing efficiency of a body-centered cubic metal

0.68 or 68%

Determine the packing efficiency of a face-centered cubic metal

0.74 or 74%

atoms anywhere else

1 shared and 1 fraction

atoms on face

2 shared and 1/2 fraction

atoms on edge

4 shared and 1/4 fraction

volume of a sphere

4πr³/3

atoms on corner

8 shared and 1/8 fraction

What determines which species in a solid solution is the solute and which is the solvent? a. the solvent in a solid solution is the one with the majority component and the solute is the one with the minority component b. the solvent in a solid solution is the one with the minority component and the solute is the one with the majority component c. The solute in a solid solution is the one with the smaller size and the solvent is the one with the large size d. The solute in a solid solution is the one with the larger size and the solvent is the one with the smaller size

A

Which of the following elements, if doped into silicon, would yield an n-type semiconductor: Ga, As, or C?

As

A Molecular-Orbital Approach

As the number of atoms in a chain increases, the energy gap between molecular orbitals (MOs) essentially disappears, and continuous bands of energy states result

Suggest an element that could be used to dope silicon to yield a p-type material.

Boron and aluminum are both good choices—both are in group 3A

For metallic structures, does the packing efficiency increase or decrease as the number of nearest neighbors decreases? a.Packing efficiency increases as the number of nearest neighbors decreases. b.Packing efficiency increases as the the volume occupied by atoms decreases compared to the volume of the unit cell. c.Packing efficiency decreases as the number of nearest neighbors decreases. d.Packing efficiency decreases as the size of the nearest neighbors decreases

C

cross-linking

Chemically bonding chains of polymers to each other can stiffen and strengthen the substance.

seven basic 3D lattices:

Cubic Tetragonal Orthorhombic Rhombohedral Hexagonal Monoclinic Triclinic

In general metals are: a. malleable b. ductile c. good conductors of heat and electricity d. all of the above

D

You generate a 3D lattice by taking a and b vectors that form a 2D square lattice. Then add a third vector c, this is of different length and perpendicular to the first two. what is it? a.Cubic b.Monoclinic c.Orthorhombic d.Tetragonal

D

nanoparticles

Different size particles of a semiconductor (like Cd3P2) can emit different wavelengths of light, depending on the size of the energy gap between bands.

properties of polymers

Stretching the polymer chains as they form can increase the amount of order, leading to a degree of crystallinity of the polymer; Interactions between chains of a polymer lend elements of order to the structure of polymers.

Crystal Lattices

a lattice of repeating shapes formed by the atoms in the crystal.

interstitial alloys

a second element fills a space in the lattice of metal atoms. (steel)

substitutional alloys

a second element takes the place of a metal atom. (14-karat gold)

The unit cell of a binary compound of copper and oxygen is shown here. Given this image and the ionic radii rCu+ = 0.74 Å and rO2 = 1.26 Å, (a) determine the empirical formula of this compound, (b) determine the coordination numbers of copper and oxygen

a) 2 b)2 c)

doping

adding impurities ( that have more (n-type) or fewer (p-type) valence electrons) to a semiconductor to increase conductivity

In crystalline solids atoms...

atoms are arranged in a very regular pattern

Nanotubes can be made from which element?

carbon (C)

vulcanization

chains are cross-linked by short chains of sulfur atoms, making the rubber stronger and less susceptible to degradation.

Amorphous solids are..

characterized by a distinct lack of order in the arrangement of atoms.

Alloys

combinations of two or more elements, the majority of which are metals.

Which of the following is not a type of cubic unit cell:

corner-centered

Molecular solids

discrete molecules that are linked to one another only by van der Waals forces. (HBr, H2O); They tend to be softer and have lower melting points (graphite)

increasing interaction strength of intermolecular forces

dispersion forces only (CH4, Br2), dipole-dipole forces (CH3F, HBr), Hydrogen bonding (NH3,CH3OH),ion-dipole forces (NaCl dissolved inH2O), ionic bonding (KBr,NH4NO3)

p-type

fewer valance electrons

Covalent-network solids

joined by an extensive network of covalent bonds. (C, Si); They tend to be hard and have high melting points (diamonds)

face-centered cubic lattice

lattice points at corners plus one lattice point at the center of each face

body-centered cubic lattice

lattice points at corners plus one lattice point in center of unit cell

primitive cubic lattice

lattice points only at corners

Addition polymer

made by coupling the monomers by converting pi bonds within each monomer to sigma bonds between monomers.

Condensation polymers

made by joining two sub units through a reaction in which a smaller molecule (often water) is also formed as a by-product. aka copolymers (ex. nylon)

Carbon nanotubes can be..

made with metallic or semiconducting properties without doping.

Polymers

molecules of high molecular mass made by monomers

n-type

more valance electrons

An important difference between crystalline solids and amorphous solid is that crystalline solids have:

repeating lattice pattern

The integrated circuits in computers are made from materials that are:

semiconductors

Ionic solids

sets of cations and anions mutually attracted to one another. (NaCl, MgO)- ion-ion interaction; have very high melting and boiling points and are quintessential crystals; different-sized ions in an ionic compound minimize the distance between oppositely charged ions while keeping like-charged ions away from each other.

Metallic solids

share a network of highly delocalized electrons. (Cu,Fe)- metallic bonding

monomers

small unit that can join together with other small units to form polymers

Which substance below has the weakest intermolecular attraction forces?

sucrose (table sugar)

The process of vulcanization involves adding which element to natural rubber?

sulfur (s)

Which of the following is NOT a type of solid:

super critical

semiconductors

there is a gap between the occupied MOs (valence band) and the unoccupied ones (conduction band); only group 4A

A material is superconducting if it is conducting electricity:

with no resistance

Which of the following is not an alloy?

zinc