Question 1

NaCl crystallizes in a face-centered cubic cell.What is the total number of ions (Na⁺ ions and Cl^- ions)that lie within a unit cell of NaCl? A)2 B)4 C)8 D)6 E)5

Accepted Answer

Each face-centered cubic unit cell contains one Na+ ion in the center and 6 Cl- ions around the edges (each shared by 4 adjacent unit cells). Therefore, there are 1 Na+ ion and (6 Cl- ions/unit cell) = 6 Cl- ions for a total of (1 + 6) = 8 ions in one unit cell of NaCl.

Question 2

The properties of graphene include ________.
A)large thermal conductivity
B)high strength
C)a zero energy gap
D)A and B
E)A, B and C

Accepted Answer

Graphene is a single layer of carbon atoms arranged in a hexagonal lattice. It has a large thermal conductivity, high strength, and a zero energy gap, making it an excellent conductor of electricity and heat. Therefore, option E, which includes all the properties mentioned, is the correct answer.

Question 3

An elastomer will fail to regain its original dimensions following a distortion beyond its ________.
A)glass transition
B)phase boundary
C)London force
D)crystallinity
E)elastic limit

Accepted Answer

The elastic limit refers to the point at which an elastomer can no longer return to its original shape and size after being stretched or compressed. Beyond this point, the material undergoes a permanent deformation and will not recover its original dimensions. The other options, such as glass transition, phase boundary, London force, and crystallinity, are not directly related to the elastic behavior of elastomers.

Question 4

Natural rubber is too soft and chemically reactive for practical applications.________ of natural rubber entails crosslinking reactive polymer chains with sulfur atoms.
A)Addition
B)Conversion
C)Vulcanization
D)Condensation
E)Polymerization

Accepted Answer

The process described in the sentence matches the definition of vulcanization, which involves crosslinking polymer chains in natural rubber with sulfur. Therefore, choice C is the best answer. Addition refers to the process of adding monomers together to form a polymer, conversion is a broad term that does not specifically relate to rubber processing, condensation involves the removal of a small molecule (such as water) to link monomers together, and polymerization is the process of forming a polymer from monomers, but it does not involve crosslinking.

Question 5

CsCl crystallizes in a unit cell that contains the Cs⁺ ion at the center of a cube that has a Cl^- at each corner.Each unit cell contains ________ Cs⁺ ion(s)and ________ Cl^- ion(s),respectively. A)1, 8 B)2, 1 C)1, 1 D)2, 2 E)2, 4

Accepted Answer

1, 1In a CsCl crystal structure, the Cs+ ion is at the center of the cube, and the Cl- ions are at the corners. Each corner atom is shared among eight adjacent cubes, so each contributes 1/8 of an ion to the unit cell. Since there are eight corners, the total contribution of Cl- ions is 1. The Cs+ ion at the center of the cube belongs entirely to the unit cell, making its contribution 1. Therefore, each unit cell contains 1 Cs+ ion and 1 Cl- ion.

Question 6

Which one of the following is an addition polymer with the same structure as polyethylene except that one hydrogen on every other carbon is replaced by a benzene ring?
A)polyvinyl alcohol
B)polystyrene
C)polyethylene
D)polyethylene glycol
E)Teflon

Accepted Answer

Polystyrene is an addition polymer with the same structure as polyethylene except that one hydrogen on every other carbon is replaced by a benzene ring, which gives it its rigid and glass-like appearance. Polyvinyl alcohol (A) is a polymer formed from the hydrolysis of polyvinyl acetate, which does not have the same structure as polyethylene. Polyethylene glycol (D) is a polymer with repeating ethylene oxide units and does not have the same structure as polyethylene. Teflon (E) is a polymer made up of repeating units of tetrafluoroethylene and does not have the same structure as polyethylene. Therefore, the best choice is B.

Question 7

An unknown metal crystallizes in a body-centered cubic structure with a unit cell edge length of 4.35 Å.The radius of the unknown atom is ________ Å.
A)1.88
B)3.77
C)2.18
D)8.70
E)4.35

Accepted Answer

In a body-centered cubic (bcc) structure, the diagonal across the body of the cube, which passes through the center, is equal to 4 times the radius of the atom (4r). This diagonal can also be calculated using the Pythagorean theorem in three dimensions as √3 times the edge length (a), so 4r = a√3. Given the edge length (a) is 4.35 Å, the radius (r) of the atom can be calculated as (4.35 Å * √3) / 4, which equals approximately 1.88 Å.

Question 8

The ________ for Ge shows it to be a semiconductor,because the gap between the filled lower and empty higher energy bands is relatively small.
A)molecular-orbital model
B)quantum mechanics model
C)atomic-orbital model
D)valence bond model
E)intermolecular model

Accepted Answer

The molecular-orbital model is used to describe the electronic structure of molecules, including semiconductors like germanium (Ge). It explains the energy bands and the gap between them, which determines semiconductor behavior.

Question 9

All of the following are classified as a nanomaterial except ________.
A)carbon nanotubes
B)buckminsterfullerene
C)isoprene
D)graphene
E)All of the above are classified as nanomaterials

Accepted Answer

Isoprene is a monomer used in the production of rubber and is not considered a nanomaterial. The other options listed are all commonly classified as nanomaterials.

Question 10

What happens to a polymer as it becomes more crystalline?
A)its melting point decreases
B)its density decreases
C)its yield stress decreases
D)its stiffness decreases
E)None of the above is correct.

Accepted Answer

As a polymer becomes more crystalline, its melting point increases, its density increases, its yield stress increases, and its stiffness increases. Therefore, none of the provided options correctly describe what happens to a polymer as it becomes more crystalline.

Question 11

How many valence electrons do inorganic compounds contain if they are considered semiconductors?
A)2
B)1
C)4
D)5
E)3

Accepted Answer

Inorganic compounds that are considered semiconductors typically have four valence electrons. This allows them to form covalent bonds and create the necessary energy band structure for semiconducting behavior. Therefore, choice C, which represents four valence electrons, is the best answer.

Question 12

The formation of a ________ polymer generally involves the elimination of a small molecule.
A)conversion
B)vulcanization
C)monomeric
D)condensation
E)polymerization

Accepted Answer

The term "condensation" refers to a reaction that results in the formation of a larger molecule by the elimination of a smaller molecule, such as water or alcohol. Therefore, the formation of a polymer by condensation typically involves the elimination of a small molecule (e.g. water) as each monomer unit is joined together to form the polymer chain.

Question 13

An unknown metal crystallizes in a primitive cubic unit cell.The length of the unit cell edge is 2.85 Å.The radius of the unknown atom is ________ Å.
A)5.70
B)1.43
C)1.85
D)1.01
E)Insufficient data is given.

Accepted Answer

In a primitive cubic unit cell, only one atom is present at the corners of the cube. The diagonal distance between opposite corners of a cube can be calculated using the Pythagorean theorem:

(diagonal)² = (a)² + (a)² + (a)²
(diagonal)² = 3a²
diagonal = √3a

In this case, the diagonal distance is equal to four times the atomic radius because it passes through the center of the cube. Therefore:

4r = √3a
r = √3a/4

Plugging in the given values:

r = √3(2.85Å)/4 = 1.43 Å

Therefore, the answer is B.

Question 14

If the electronic structure of a solid substance consists of a valence band that is completely filled with electrons and there is a large energy gap to the next set of orbitals,then this substance will be a(n)________.
A)alloy
B)insulator
C)conductor
D)semiconductor
E)nonmetal

Accepted Answer

A completely filled valence band with a large energy gap to the next set of orbitals means that it requires a large amount of energy for electrons to move into the conduction band and become mobile. This lack of mobile electrons makes the substance a poor conductor, thus making it an insulator.

Question 15

Molecular solids consist of atoms or molecules held together by ________.
A)dipole-dipole forces only
B)Metallic bonds only
C)London dispersion forces and hydrogen bonds only
D)hydrogen bonds only
E)dipole-dipole forces, London dispersion forces, and/or hydrogen bonds

Accepted Answer

Molecular solids consist of discrete molecules held together by intermolecular forces such as dipole-dipole forces, London dispersion forces, and/or hydrogen bonds. Metallic bonds are not present in molecular solids as they involve the delocalization of electrons in a metal lattice.

Question 16

The process of ________ can produce an n-type semiconductor,which can greatly increase intrinsic conductivity.
A)melting
B)fusing
C)doping
D)mixing
E)infusing

Accepted Answer

The word "doping" refers to the introduction of impurities into a semiconductor in order to change its electrical properties. One common method of doping is to introduce impurities such as phosphorus or arsenic, which have extra electrons. These extra electrons can move freely within the crystal lattice, creating an excess of negative charge carriers and making the semiconductor n-type (i.e. with a negative charge). This greatly increases its intrinsic conductivity.

Question 17

CsCl crystallizes in a unit cell that contains a Cs⁺ ion at the center of a cube and a Cl^- ion at each corner.The unit cell of CsCl is ________. A)close packed B)body-centered cubic C)face-centered cubic D)amorphous E)primitive cubic

Accepted Answer

CsCl crystallizes in a body-centered cubic unit cell, which is characterized by a single atom/ion at its center and one atom/ion at each of its eight corners. The arrangement of Cs+ and Cl- ions in CsCl crystal structure is such that it forms a cubic lattice with the Cs+ ions occupying the body-centered position and the Cl- ions occupying the corner positions.

Question 18

KF crystallizes in a face-centered cubic cell.What is the total number of ions (K⁺ ions and F^- ions)that lie within a unit cell of KF? A)2 B)8 C)6 D)5 E)4

Accepted Answer

In a face-centered cubic cell, there are 4 ions located at the corners and 4 ions located at the center of the faces. For KF, the unit cell contains one K+ ion and one F- ion. Thus, there are a total of 8 ions (4 K+ and 4 F-) within a unit cell of KF.

Question 19

The empirical formula of an addition polymer ________.
A)is the same as that of the monomer from which it is formed except that 2 H and 1 O have been subtracted
B)is the same as that of the monomer from which it is formed except that 1 H and 2 O have been subtracted
C)is the same as that of the monomer from which it is formed except that 2 H and 1 C have been added
D)is the same as that of the monomer from which it is formed
E)is different than that of the monomer from which it is formed

Accepted Answer

The empirical formula of an addition polymer is the same as that of the monomer from which it is formed. This is because addition polymerization involves the repeated addition of monomer units to form a polymer chain, without any removal or addition of atoms. Therefore, the ratio of atoms in the monomer and polymer remains the same, resulting in the same empirical formula.

Question 20

All of the following are natural polymers except ________.
A)silk
B)starch
C)nylon
D)protein
E)cellulose

Accepted Answer

Nylon is a synthetic polymer, not a natural polymer like silk, starch, protein, and cellulose.

Quiz 12: Solids and Modern Materials

NaCl crystallizes in a face-centered cubic cell.What is the total number of ions (Na⁺ ions and Cl^- ions) that lie within a unit cell of NaCl?

The properties of graphene include ________.

An elastomer will fail to regain its original dimensions following a distortion beyond its ________.

Natural rubber is too soft and chemically reactive for practical applications.________ of natural rubber entails crosslinking reactive polymer chains with sulfur atoms.

CsCl crystallizes in a unit cell that contains the Cs⁺ ion at the center of a cube that has a Cl^- at each corner.Each unit cell contains Cs⁺ ion(s) and Cl^- ion(s) ,respectively.

Which one of the following is an addition polymer with the same structure as polyethylene except that one hydrogen on every other carbon is replaced by a benzene ring?

An unknown metal crystallizes in a body-centered cubic structure with a unit cell edge length of 4.35 Å.The radius of the unknown atom is ________ Å.

The ________ for Ge shows it to be a semiconductor,because the gap between the filled lower and empty higher energy bands is relatively small.

All of the following are classified as a nanomaterial except ________.

What happens to a polymer as it becomes more crystalline?

How many valence electrons do inorganic compounds contain if they are considered semiconductors?

The formation of a ________ polymer generally involves the elimination of a small molecule.

An unknown metal crystallizes in a primitive cubic unit cell.The length of the unit cell edge is 2.85 Å.The radius of the unknown atom is ________ Å.

If the electronic structure of a solid substance consists of a valence band that is completely filled with electrons and there is a large energy gap to the next set of orbitals,then this substance will be a(n) ________.

Molecular solids consist of atoms or molecules held together by ________.

The process of ________ can produce an n-type semiconductor,which can greatly increase intrinsic conductivity.

CsCl crystallizes in a unit cell that contains a Cs⁺ ion at the center of a cube and a Cl^- ion at each corner.The unit cell of CsCl is ________.

KF crystallizes in a face-centered cubic cell.What is the total number of ions (K⁺ ions and F^- ions) that lie within a unit cell of KF?

The empirical formula of an addition polymer ________.

All of the following are natural polymers except ________.