ch 21 and 12 (test 5)
hydrogen bonding, dipole dipole, dispersion forces
12.13 What kinds of attractive forces exist between particles (atoms, molecules, or ions) in a)molecular crystals,
covalent chemical bonds
12.13 What kinds of attractive forces exist between particles (atoms, molecules, or ions) in b)covalent-network crystals,
ionic bonds
12.13 What kinds of attractive forces exist between particles (atoms, molecules, or ions) in c)ionic crystals,
metallic bonds
12.13 What kinds of attractive forces exist between particles (atoms, molecules, or ions) in d)metallic crystals?
metallic
12.17 You are given a gray substance that melts at 700 °C; the solid is a conductor of electricity and is insoluble in water. Which type of solid (molecular, metallic, covalent-network, or ionic) might this substance be?
2
12.27 What is the minimum number of atoms that could be contained in the unit cell of an element with a body-centered cubic lattice?
NiAs
12.29 The unit cell of nickel arsenide is shown here. What is the empirical formula?
primitive hexagonal
12.29 The unit cell of nickel arsenide is shown here. What type of lattice does this crystal possess?
b
12.33 Consider the unit cells shown here for three different structures that are commonly observed for metallic elements. Which structure(s) corresponds to the least dense packing of atoms?
a and c
12.33 Consider the unit cells shown here for three different structures that are commonly observed for metallic elements. Which structure(s) corresponds to the densest packing of atoms?
false
12.49 State whether each sentence is true or false: Metals have high electrical conductivities because they are denser than other solids.
false
12.49 State whether each sentence is true or false: Metals have large thermal conductivities because they expand when heated.
false
12.49 State whether each sentence is true or false: Metals have small thermal conductivities because the delocalized electrons cannot easily transfer the kinetic energy imparted to the metal from heat.
true
12.49 State whether each sentence is true or false: Metals have high electrical conductivities because the electrons in the metal are delocalized.
true
12.67 Classify each of the following statements as true or false: Other factors being equal, highly symmetric molecules tend to form solids with higher melting points than asymmetrically shaped molecules.
false
12.67 Classify each of the following statements as true or false: Although both molecular solids and covalent-network solids have covalent bonds, the melting points of molecular solids are much lower because their covalent bonds are much weaker.
covalent-network solids
12.69 Both covalent-network solids and ionic solids can have melting points well in excess of room temperature, and both can be poor conductors of electricity in their pure form. However, in other ways their properties are quite different. Which type of solid can become a considerably better conductor of electricity via chemical substitution?
ionic solids
12.69 Both covalent-network solids and ionic solids can have melting points well in excess of room temperature, and both can be poor conductors of electricity in their pure form. However, in other ways their properties are quite different. Which type of solid is more likely to dissolve in water?
GaAs
12.71 For each of the following pairs of semiconductors, which one will have the larger band gap: GaAs or InAs?
GaN
12.71 For each of the following pairs of semiconductors, which one will have the larger band gap: GaN or InP,
CdS
12.71 For each of the following pairs of semiconductors, which one will have the larger band gap: CdS or CdTe,
a
12.9 shown here are cartoons of two different polymers. Which of these polymers would you expect to be more crystalline?
a
12.9 shown here are cartoons of two different polymers. Which of these polymers would you expect to have a higher melting point?
molecular chains
12.91 What molecular features make a polymer flexible? Flexibility of the _______ _______ causes flexibility of the bulk polymer. Flexibility is enhanced by molecular features that inhibit order, such as branching, and diminished by features that encourage order, such as cross-linking or delocalized π electron density.
low degree
12.93 If you want to make a polymer for plastic wrap, should you strive to make a polymer that has a high or low degree of crystallinity?
false
12.97 Indicate whether each statement is true or false: The light that is emitted from a semiconductor, upon external stimulation, becomes longer in wavelength as the particle size of the semiconductor decreases.
false
12.97 Indicate whether each statement is true or false: The band gap of a semiconductor decreases as the particle size decreases in the 1-10-nm range.
beta emission
21.19 Predict the type of radioactive decay process for the following radionuclides: b)68:29 Cu,
beta emission
21.19 Predict the type of radioactive decay process for the following radionuclides: c)phosphorus-32,
beta emission
21.19 Predict the type of radioactive decay process for the following radionuclides: d)chlorine-39.
positron emission
21.19 Predict the type of radioactive decay process for the following radionuclides: a)85:58B,
b
21.27 Which statement best explains why nuclear transmutations involving neutrons are generally easier to accomplish than those involving protons or alpha particles? a) Neutrons are not a magic number particle. b) Neutrons do not have an electrical charge. c) Neutrons are smaller than protons or alpha particles. d)Neutrons are attracted to the nucleus even at long distances, whereas protons and alpha particles are repelled.
b
21.53 which nuclei are likely to have the largest mass defect per nucleon? a) boron-11 b) vanadium-51 c) tin-118 d) copper-243
control rods
21.59 what is the function of the _____ _____ in a nuclear reactor?--to block the paths of neutrons, keeping the system from reaching a dangerous supercritical mass
crystallinity
A measure of the extent of crystalline character (order) in a polymer.
compound semiconductors
A semiconducting material formed from two or more elements. Maintains the same average valence electron count as elemental semiconductors
thermosetting plastic
A type of plastic that once formed into a shape, cannot be reformed into a different shape.
decrease
As the cation/anion ratio goes down, there are fewer cations to surround each anion, and so the anion coordination number must __________ (increase/decrease). The empirical formula of an ionic compound can be described quantitatively by the relationship
increases
As the difference in electronegativity of the elements ________ (increases/decreases), the bonding becomes more polar and the band gap increases.
insulator
Band gaps greater than ∼3.5 eV∼3.5 eV are so large that the material is not a semiconductor; it is an ________ and does not conduct electricity.
hexagonal close packing
Continuing with this pattern, the fourth layer would lie directly over the spheres in the second layer, leading to the ABAB stacking pattern seen on the left, which is called ______ ______ _____
less flexible
If you cross-link a polymer, is it more flexible or less flexible than it was before?
heterogenous
In a ________ alloy, the components are not dispersed uniformly
coordination number
In both hexagonal close packing and cubic close packing, each sphere has 12 equidistant nearest neighbors: six neighbors in the same layer, three from the layer above, and three from the layer below. We say that each sphere has a _____ ______ of 12. The ______ ________is the number of atoms immediately surrounding a given atom in a crystal structure.
thermoplastics
Materials that can be repeatedly softened by heating and hardened by cooling. Examples include acrylic, pvc, and nylon.
semiconductors
Metals conduct electricity extremely well. Many solids, however, conduct electricity somewhat, but nowhere near as well as metals, which is why such materials are called ________
higher
Moving from left to right across the d-orbital metals section of the periodic table, the number of valence electrons, occupancy of the bonding band, and strength of metallic bonding increase. Stronger metallic bonding requires more energy to break bonds and mobilize atoms, resulting in ______ melting points
condensation polymerization
Polymerization in which molecules are joined together through condensation reactions. A small molecule is eliminated, such as H2O
solid solutions
Substitutional and interstitial alloys are both homogeneous mixtures in which components are dispersed randomly and uniformly (Figure 12.15). (Section 1.2) Solids that form homogeneous mixtures are called ______ ______
elemental
The _________ semiconductors all come from group 4A. As we move down the periodic table, bond distances increase, which decreases orbital overlap. This decrease in overlap reduces the energy difference between the top of the valence band and the bottom of the conduction band. As a result, the band gap decreases on going from diamond (5.5 eV, an insulator) to silicon (1.11 eV) to germanium (0.67 eV) to gray tin (0.08 eV). In the heaviest group 4A element, lead, the band gap collapses altogether. As a result, lead has the structure and properties of a metal.
increase
The band gap of a compound semiconductor tends to (increase/decrease) as the difference in group numbers increases
delocalized
The bonding, called metallic bonding, happens because the valence electrons are _________throughout the entire solid. That is, the valence electrons are not associated with specific atoms or bonds but are spread throughout the solid
thermal conductivity
The high _______ _______ of metals is also accounted for by the presence of mobile electrons. The movement of electrons in response to temperature gradients permits ready transfer of kinetic energy throughout the solid.
substitutional alloy
When atoms of the solute in a solid solution occupy positions normally occupied by a solvent atom, we have a _______ _______
interstitial alloy
When the solute atoms occupy interstitial positions in the "holes" between solvent atoms, we have an _______ _______
potassium 40
Which is radioactive? potassium-39 or potassium-40
As
Which of the following elements, if doped into silicon, would yield an n-type semiconductor: Ga, As, or C? (hint: look for the element with more valence electrons than silicon)
ethene
Which of these molecules can be used as a monomer: ethanol, ethene (also called ethylene), methane?
alloy
___ is a material that contains more than one element and has the characteristic properties of a metal.
ionic solids
_____ _____ are held together by the mutual electrostatic attraction between cations and anions
Molecular solids
_____ ______ are held together by the intermolecular forces we studied in Chapter 11: dispersion forces, dipole-dipole interactions, and hydrogen bonds. Because these forces are relatively weak, molecular solids tend to be soft and have low melting points.
metallic solids
______ _____ are held together by a delocalized "sea" of collectively shared valence electrons
magic numbers
______ _______•2, 8, 20, 28, 50, or 82 protons or 2, 8, 20, 28, 50, 82, or 126 neutrons result in more stable nuclides.
covalent-network solids
______-______ _____ are held together by an extended network of covalent bonds. This type of bonding can result in materials that are extremely hard, like diamond, and it is also responsible for the unique properties of semiconductors.
Polymers
_______ are normally stronger and have higher melting points than molecular solids, and they are more flexible than metallic, ionic, or covalent-network solids
Polymers
_______ contain long chains of atoms (usually carbon), where the atoms within a given chain are connected by covalent bonds and adjacent chains are held to one another largely by weaker intermolecular forces
Nanomaterials
___________ are solids in which the dimensions of individual crystals have been reduced to the order of 1-100 nm
metallic bonds
a bond formed by the attraction between positively charged metal ions and the electrons around them
elastomer
a material that can undergo a substantial change in shape via stretching, bending, or compression and return to its original shape upon release of the distorting force (ex: rubber)
p-type semiconductor
a semiconductor that has been mixed with atoms with fewer valence electrons, leaving holes for other valence electrons to enter, increasing conductivity
n-type semiconductor
a substance whose conductivity is increased by doping it with atoms having more valence electrons than the atoms in the host crystal
addition polymerization
a type of polymerization in which the monomers simply add together to form the polymer, with no other products
doping
adding impurities to a semiconductor to increase conductivity
band gap
an energy gap that exists between the valence band and conduction band of semiconductors and insulators
monomers
building blocks of polymers; molecules of low molecular weight
middle
elements near the _______ of the transition metal series, rather than those at the end, have the highest melting points in their respective periods (Figure 12.21). This trend implies that the strength of metallic bonding first increases with increasing number of electrons and then decreases. Similar trends are seen in other physical properties of the metals, such as the boiling point, heat of fusion, and hardness
positron emission
for low atomic numbers, _______ ______ is more common than electron capture
1:1
for smaller nuclei (Z< or = 20) stable nuclei have a neutron to proton ration close to __:__
positron or electron capture
indicate which are in the belt of stability, if they are not describe the decay process: chlorine-32:17
beta decay
indicate which are in the belt of stability, if they are not describe the decay process: neon-24:10
alpha decay
indicate which are in the belt of stability, if they are not describe the decay process: polonium-216:84 (hint: look at the atomic number)
beta decay
indicate which are in the belt of stability, if they are not describe the decay process: tin-108:50
polymers
large compound formed from combinations of many monomers; molecules of high molecular weight
more
nuclei with an even number of protons and neutrons tend to be _____ (more/less) stable than those with odd numbers
copolymers
polymers formed from two different monomers
vulcanization
process of treating rubber to make it more useful
conduction band
semiconductors an energy gap develops between the filled and empty states, much like the energy gap between bonding and antibonding orbitals. (Section 9.6) The band that forms from bonding molecular orbitals is called the valence band, and the band that forms the antibonding orbitals is called the _______ ________
plastics
synthetic polymers that can be molded or shaped
cubic close packing
the third-layer spheres could lie directly over the depressions that were marked with red dots in the first layer. In this arrangement, the spheres in the third layer do not sit directly above the spheres in either of the first two layers, as shown by the dashed red lines on the lower right-hand side of Figure 12.13. If this sequence is repeated in subsequent layers, we derive an ABCABC stacking pattern shown on the right known as ______ _______ _____
a
which has more ordered regions? (which would correspond to being more crystalline and a higher melting point)
bismuth 208
which is radioactive bismuth-209 or bismuth-208
nickel 65
which is radioactive? nickel-58 or nickel-65
