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Chem 409 > Chapter 6 - Structures and energetics of metallic and ionic solids > Flashcards

Chapter 6 - Structures and energetics of metallic and ionic solids Flashcards

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1
Q

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

A

74%

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2
Q

Hexagonal close-packing arrangement

A

ABABAB

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3
Q

Cubic close-packing arrangement

A

ABCABC

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4
Q

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

A

12 (coordination number of 12)

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5
Q

Unit cell

A

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

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6
Q

Cubic close-packing is also called

A

face-centered cubic packing

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7
Q

Simple cubic coordination number

A

6

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8
Q

Body centered cubic coordination number

A

8

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9
Q

The packing of spheres model is applicable to

A

group 18 elements, metals, and H2 and F2

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10
Q

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

A

ccp

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11
Q

Most metals crystallize with ___, ___, or ___ lattices

A

ccp, hcp, or bcc

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12
Q

Bcc packing efficiency

A

68%

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13
Q

Polymorph

A

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

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14
Q

Metallic radius

A

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

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15
Q

Alloy

A

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

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16
Q

In a substitutional alloy,

A

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).

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17
Q

In interstitial alloys,

A

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.

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18
Q

In intermetallic alloys,

A

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

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19
Q

The electrical conductivity of a metal decreases with

A

an increase in temperature.

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20
Q

The electrical conductivity of a semiconductor decreases with

A

a decrease in temperature.

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21
Q

Electrical resistance increases as temperature increases because

A

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

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22
Q

A band is

A

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.

23
Q

Valence band

A

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

24
Q

Conduction band

A

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

25
Q

Conductors have ________ between their valence and conducting bands.

A

overlap

26
Q

Insulators have _______ between their valence and conducting bands.

A

a gap

27
Q

A band gap occurs when

A

there is a significant energy difference between two bands.

28
Q

Fermi level

A

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

29
Q

Fermions

A

Particles with half-integer spin such as electrons.

30
Q

Intrinsic semiconductor

A

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

31
Q

A charge carrier in a semiconductor is either

A

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

32
Q

Dopant

A

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

33
Q

P-type semiconductor

A

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.

34
Q

N-type semiconductor

A

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.

35
Q

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

A

equal.

36
Q

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

A

half that of M.

37
Q

Rock salt structure

A

MX

Coordination number = 6

38
Q

Fluorite structure

A

MX2

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

39
Q

Zinc blende structure

A

MX

Coordination number = 4

40
Q

Cesium chloride structure

A

MX

Coordination number = 8

41
Q

Antifluorite structure

A

M2X

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

42
Q

Rutile structure

A

MX2

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

43
Q

Lattice energy

A

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

44
Q

The Madelung constant is used in determining

A

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

45
Q

Born forces

A

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

46
Q

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

A

50

47
Q

A species disproportionates if

A

it undergoes simultaneous oxidation and reduction.

48
Q

Intrinsic defects occur in

A

lattices of pure compounds.

49
Q

Extrinsic defects result from

A

the addition of dopants.

50
Q

A Schottky defect arises from

A

vacant lattice sites.

51
Q

Frenkel defect

A

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.

52
Q

A tetrahedral hole can accommodate a sphere with a radius

A

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

53
Q

An octahedral hole can accommodate a sphere with a radius

A

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

54
Q

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

A

8

Chem 409 (9 decks)

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