Chapter 6 - Structures and energetics of metallic and ionic solids

Question 1

In close-packing of spheres, how much of the space is occupied by spheres?

Answer 1

74%

Question 2

Hexagonal close-packing arrangement

Answer 2

ABABAB

Question 3

Cubic close-packing arrangement

Answer 3

ABCABC

Question 4

In hexagonal and cubic close packing, each sphere is surrounded by _____ nearest neighbors.

Answer 4

12 (coordination number of 12)

Question 5

Unit cell

Answer 5

The smallest repeating unit of a structure which carries all the information needed to construct an infinite lattice.

Question 6

Cubic close-packing is also called

Answer 6

face-centered cubic packing

Question 7

Simple cubic coordination number

Answer 7

6

Question 8

Body centered cubic coordination number

Answer 8

8

Question 9

The packing of spheres model is applicable to

Answer 9

group 18 elements, metals, and H2 and F2

Question 10

Noble gases (except He and Rn) have _____ crystalline structures.

Answer 10

ccp

Question 11

Most metals crystallize with ___, ___, or ___ lattices

Answer 11

ccp, hcp, or bcc

Question 12

Bcc packing efficiency

Answer 12

68%

Question 13

Polymorph

Answer 13

The existence of a solid material in more than one form or crystal structure.

Question 14

Metallic radius

Answer 14

Half of the distance between the nearest-neighbor atoms in a solid state metal lattice, and is dependent upon coordination number.

Question 15

Alloy

Answer 15

An intimate mixture, or in some cases, a compound of two or more metals, or non-metals.

Question 16

In a substitutional alloy,

Answer 16

atoms of the solute occupy sites in the lattice of the solvent metal (both atoms must be similar in size and tolerate the same coordination environment).

Question 17

In interstitial alloys,

Answer 17

an atom of radius 0.41 times that of the atoms in the close-packed array can occupy an octahedral whole, while significantly smaller atoms may be accommodated in tetrahedral holes.

Question 18

In intermetallic alloys,

Answer 18

when metal mixtures solidify, the alloy formed may possess a definite structure type that is different from those of the pure metals.

Question 19

The electrical conductivity of a metal decreases with

Answer 19

an increase in temperature.

Question 20

The electrical conductivity of a semiconductor decreases with

Answer 20

a decrease in temperature.

Question 21

Electrical resistance increases as temperature increases because

Answer 21

thermal vibrations of the nuclei increase and don’t allow a straight path for the electrons to flow through.

Question 22

A band is

Answer 22

a group of MOs, the energy differences between which are so small that the system behaves as if a continuous, non-quantized variation of energy within the band is possible.

Question 23

Valence band

Answer 23

the band of electron orbitals that electrons can jump out of, moving into the conduction band when excited.

Question 24

Conduction band

Answer 24

the band of electron orbitals that electrons can jump up into from the valence band when excited.

Question 25

Conductors have ________ between their valence and conducting bands.

Answer 25

overlap

Question 26

Insulators have _______ between their valence and conducting bands.

Answer 26

a gap

Question 27

A band gap occurs when

Answer 27

there is a significant energy difference between two bands.

Question 28

Fermi level

Answer 28

The highest energy level that an electron can occupy at the absolute zero temperature.

Question 29

Fermions

Answer 29

Particles with half-integer spin such as electrons.

Question 30

Intrinsic semiconductor

Answer 30

A material that behaves as a semiconductor without the addition of dopants.

Question 31

A charge carrier in a semiconductor is either

Answer 31

a positive hole or an electron that is able to conduct electricity.

Question 32

Dopant

Answer 32

An impurity introduced into a semiconductor in minute amounts to enhance its electrical conductivity.

Question 33

P-type semiconductor

Answer 33

An electron deficient site is introduced (like exchanging group 13 for group 14). This creates a positive hole in which it can be thought that the positive hole moves in the opposite direction of the current.

Question 34

N-type semiconductor

Answer 34

An electron rich site is introduced (like exchanging group 15 for group 14). These extra electrons are in a donor level below the conduction band and can populate the conduction band and move freely.

Question 35

In salts of formula MX, the coordination numbers of M and X must be

Answer 35

equal.

Question 36

In salts of formula MX2, the coordination number of X must be

Answer 36

half that of M.

Question 37

Rock salt structure

Answer 37

MX | Coordination number = 6

Question 38

Fluorite structure

Answer 38

MX2 | Coordination number = 8 (M) and 4 (X)

Question 39

Zinc blende structure

Answer 39

MX | Coordination number = 4

Question 40

Cesium chloride structure

Answer 40

MX | Coordination number = 8

Question 41

Antifluorite structure

Answer 41

M2X | Coordination number = 4 (M) and 8 (X)

Question 42

Rutile structure

Answer 42

MX2 | Coordination number = 6 (M) and 3 (X)

Question 43

Lattice energy

Answer 43

The change in internal energy that accompanies the formation of one mole of the solid from its constituent gas-phase ions at 0 K.

Question 44

The Madelung constant is used in determining

Answer 44

the electrostatic potential of a single ion in a crystal by approximating the ions by point charges.

Question 45

Born forces

Answer 45

Electron-electron and nucleus-nucleus repulsions due to the finite size of ions in an ionic lattice.

Question 46

Madelung constants for MX2 structures are approximately ____ % higher than those for MX lattices

Answer 46

50

Question 47

A species disproportionates if

Answer 47

it undergoes simultaneous oxidation and reduction.

Question 48

Intrinsic defects occur in

Answer 48

lattices of pure compounds.

Question 49

Extrinsic defects result from

Answer 49

the addition of dopants.

Question 50

A Schottky defect arises from

Answer 50

vacant lattice sites.

Question 51

Frenkel defect

Answer 51

In ionic lattices in which there is a significant difference in size between the cation and anion, the smaller ion may occupy a site that is vacant in the ideal lattice.

Question 52

A tetrahedral hole can accommodate a sphere with a radius

Answer 52

<= 0.23 times that of the close-packed spheres.

Question 53

An octahedral hole can accommodate a sphere with a radius

Answer 53

<= 0.41 times that of the close-packed spheres.

Question 54

Metals with coordination numbers less than ____ are among those that are the most volatile.

Answer 54

8