133B- solid chem

Question 1

what type of packing are these

Answer 1

Question 2

what is a unit cell of ccp

Answer 2

Question 3

what is a unit cell of ccp

Answer 3

Question 4

What is the only element forming primitive cubic

Answer 4

palladium

Question 5

What elements form body centred cubic

Answer 5

metals

Question 6

equation for packing efficiency

Answer 6

Question 7

How to work out the volume of atoms in a unit cell in ccp

Answer 7

Question 8

How to work out the packing efficiency for ccp

Answer 8

Question 9

out of
hexagonal close packing,
cubic close packing,
body centred cubic and
primitive cubic,
which structures are the best at packing

Answer 9

ccp

Question 10

How does the energy of the 2s orbital in lithium change between Li, Li2, Li3, li4 etc.

Answer 10

molecular orbitals getting closer in energy when atom no increases resulting in a ‘band’

Question 11

What must a material have to conduct electricity

Answer 11

partially filled conduction band

Question 12

What type of alloy is this

Answer 12

substitutional- atoms of one metal are exchanged for those of another metal/ sizes of atoms must be similar
-happens randomly in sub alloys and diagram inst a repeating unit

Question 13

What type of alloy is this

Answer 13

interstitial- new atom sits in interstitial position/ atoms of one element are present in the interstitial sites of a metal lattice

Question 14

NaCl- what are positions of the chloride and sodium ions

Answer 14

-cubic close packing/ fcc of chlorine ions
-sodium are on edges and in middle so octrahedral interstitial sites [forms 6 bonds]

large anion usually gives lattice and smaller gives interstitial (cation)

Question 15

FeS2 has the same structure as NaCl . Where would the Fe cations and S2 anions be

Answer 15

Fe 2+ would be where the sodium Ions are/ S2 are bonded together as a pair (-2 together) and sit where the chlorine would

Question 16

What type of tetrahedral packing is this in ZnS

Answer 16

S only filling half the tetrahedral sites/ alternating

Question 17

What type of packing does each element have and what site is half filled

Answer 17

For both structures anions are close packed and the cations occupy half of the octahedral sites.
CdCl2 has ABC packing
CdI2 has ABA packing

-octrahedral sites half filled by Cd in the CdCl2 still

Question 18

G1 halides have sodium structure, what is the exception to this

Answer 18

caesium

Question 19

Describe the sites of Ti (blue) and O2 (red)
[The structure is not cubic as one unit cell length is longer than the other two]

Answer 19

Ti is on the edges and in the middle,
Ti is octrahedral [as it forms 6 bonds] and O is trigonal planar [forms 3]

Question 20

What do all calculations assume about the atoms/ions in a unit cell
and what is the assumptions of ions in a lattice structure

Answer 20

ions are charged, fixed-sized hard spheres
and
In an ionic solid, the ions are assumed to be in contact with their nearest neighbour of the opposite charge (used for equation r/r)

Question 21

What are the trends in ionic radii across a period and across the whole table

Answer 21

-Ionic radii increase down a group (increasing principal quantum no)
-cations are generally smaller than anions
-cations get smaller with increasing charge and anions get bigger with increasing charge

Question 22

What is the difference between an insulator and semi conductor conduction band

Answer 22

insulators- large gap so there in no electrons sitting in empty band so no conduction. electrons don’t have enough thermal energy to move there.
semiconductor- gap is smaller so heating could give e- enough energy

Question 23

What dictates which alloy is made

Answer 23

size of new atom coming in

Question 24

Which atomisation value would you use for this harber cycle ΔaH(Cl) or ΔaHo(Cl2)

Answer 24

ΔaHo(Cl)- this is bond dissociation for 1 mole of Cl gas to one mole Cl- ions wheras
ΔaHo(Cl2)- would need to be halved as it is 1 mole Cl2 gas to 2 moles Cl- ions

Question 25

There are different definitions for '**electron gain enthalpy**' (adding an electron to make an ion e.g adding electron to chlorine). Another name for it is electron affinity but what is different about that definition

Answer 25

electron affinity is same value but opposite sign

Question 26

what is the packing of the anions and cations

Answer 26

**cubic close packing** of calcium cations with the fluoride anions in the **tetrahedral interstitial sites**

Question 27

What do we assume about the equation below when doing lattice calculations

Answer 27

assume H and U are the same U= heat change constant volume H=U +pV diff between lattice enthalpy and lattice energy is normally relatively small and can usually be ignored.

Question 28

what does 1/n take account for

Answer 28

repulsive energy from electron clouds

Question 29

what does n stand for (Born exponent)

Answer 29

compressibility of a compound/element and is dependant on its amount of electrons

Question 30

Do you need to take into account positive and negative signs for z in the calculation

Answer 30

no- if if its MgO, z would be +2 for both of them so the calculation would be 2x2

Question 31

What will the n of NaCl be

Answer 31

n=8; **average** between the n of both ions

Question 32

How does the lattice energy change between structures that have low charge ions and ones that have high charge ones

Answer 32

higher charges will have higher lattice E, e.g MgO will have higher lattice E than NaCl

Question 33

What does the Madelung constant depend on

Answer 33

the structure- e.g something with the same structure as NaCl will have the same Madelung constant

Question 34

if calc lattice E is lower than expected lattice E the covalent character is high/low

Answer 34

high

Question 35

if calc lattice E and expected lattice E are similar covalent character is high/low

Answer 35

low

Question 36

How do the units of r and U differ from equations

Answer 36

Kapustinskii- r= pcm and will give answer in KJmol-1 Born-Landé - r=m and answer is in J

Question 37

What is the difference between the Kapustinskii and Madelung equations

Answer 37

Kapustinskii is more of an approximation than Madelung

Question 38

equation for radius ratio and what does it tell you

Answer 38

limiting radius ratio- the **smallest possible value of the radius ratio** for the cations and anions **to be contact.** If the radius ratio is any smaller, the action-anion contact is lost.

Question 39

****question still to do What is the packing efficiency of the body-centred cubic structure

Question 40

greater electronegativity greater degree ionic bond, what type of bonding when electrongetavities are low

Answer 40

alloy, with metallic bonding

Question 41

Na and K have low electrongetavites and little difference between them

Question 42

what is the cell projection diagram for this structure and what is this packing called

Answer 42

ccp/ close cubic packed -must have the key beside

Question 43

What does this key mean

Answer 43

the yellow spheres are the first and last layer (which must be the same as the top and bottom are repeating units) the blue dots are the middle layer as they are in between 0-1 and are 0.5 so must be halfway between top and bottom

Question 44

cell projection diagram of body-centred cubic/bcc structure

Answer 44

Question 45

cell projection diagram of hexagonal close-packed/ hcp

Answer 45

Question 46

density equation

Answer 46

mass per unit volume

Question 47

To work out the density of a unit cell you need its mass and volume. How do you work out the mass and volume of the unit cell ccp

Answer 47

mass = moles x RAM, multiply the Mr by the number of atoms (4), then divide by avagadros constant which will give you gmol-1 for ccp the volume is always **L^3 = (8)3/2 x r^3**

Question 48

what is the free space in a unit cell called

Answer 48

interstitial sites

Question 49

which site is octrahedral and which is tetrahedral

Answer 49

Question 50

for any close packed structure what is true of the ratio between atoms, hexagonal sites and tetrahedral sites ccp (fcc)/ hcp

Answer 50

Question 51

what structures are **not** close packing

Answer 51

bcc and primitive cubic

Question 52

which atoms have at octrahedral sites around them in ccp

Answer 52

everything along the middle line

Question 53

what positions do the tetrahedral sites lie at

Answer 53

Question 54

in **cubic closed packed** the tetrahedral sites share faces/edges and the octrahedral sites share faces/edges

Answer 54

Both sites share **edges**

Question 55

in **hexagonal closed packed** the tetrahedral sites share faces/edges and the octrahedral sites share faces/edges

Answer 55

both share **faces**

Question 56

which element does the tetrahedral sites fill

Answer 56

F2

Question 57

Describe the packing of CaF2

Answer 57

Ca- cubic close packing F2- tetrahedral interstitial sites (second picture is if you had 4 units repeating next to the one shown) The related structure in which there is a ccp arrangement of anions with cations in the tetrahedral sites is called the antifluorite structure

Question 58

how many tetrahedral sites are there per atom in a close packed structure [I don't know what this means]

Answer 58

2

Question 59

How is CaF2 the anti flouride structure of NaCl

Answer 59

In NaCl- the anions are in close packed and the cations in the interstitial sites However in CaF2, the opposite is true/ cations are in the close packed arrangement

Question 60

What are the arrangement of ions in NiAs Ni= cation As= anion

Answer 60

Ar- hexagonal close packing Ni- cations in the octahedral interstitial sites The NiAs structure is often adopted by compounds with high covalent character

Question 61

What type of compound would adopt this structure

Answer 61

components with a high covalent character

Question 62

What's the general rule when trying to find out the packing of a structure

Answer 62

one element will have a **close packing structure** and one will be in the interstitial site

Question 63

What are all the types of **close packing structures** and which are the two that are not

Answer 63

close packing ccp and hcp bcc and primitive are not close packing

Question 64

Show the empirical formula is CaTiO3

Answer 64

Question 65

Answer 65

Question 66

What is the sin rule

Answer 66

Question 67

How would you work out the limiting radius ratio (r+/r-) for something with a sodium chloride structure and what does this ratio represent

Answer 67

0.414 is the smallest value of the radius ratio for the NaCl structure for which the cations and anions are in contact. If the radius ratio is smaller, the cation-anion contact is lost and the structure becomes less stable than one with a lower coordination number

Question 68

What happens when the radius ratio becomes smaller than the limiting radius ratio

Answer 68

the cation-anion contact is lost and the structure becomes **less stable than one with a lower coordination number**

Question 69

How would you work out the limiting radius ratio (r+/r-) for something with a tetrahedral structure

Answer 69

Question 70

What are their limiting radius ratios

Answer 70

Question 71

Answer 71

Question 72

A from the NaCl structure= 1.7476

Answer 72

Question 73

define lattice enthalpy

Answer 73

enthalpy change for the conversion of one mole of the ionic solid into the gaseous ions

Question 74

Use the Kapustinskii equation to figure out the lattice energy of LiCl and AgCl k =107900pmkJmol–1,

Answer 74

Question 75

What is the van Arkel– Ketelaar triangle

Answer 75

predicts the type of bonding a compound has dependant on the electronegativity of its elements x axis- χ̅ **average** electronegativity over the two elements y axis- Δχ difference in electronegativity

Question 76

Estimate where MgF2 and MgI2 would be on a van Arkel-Ketelaar triangle

Answer 76