Electronic Properties

Question 1

Conductivity

Answer 1

ability to conduct electrical current
electrons flow = electric current 
S m -1 
sigma = N x Ze x u
density of electrons x charge x velocity

Question 2

Conductance

Answer 2

object property
conductance = conductivity x area/length
S

Question 3

Sigma Values

Answer 3

insulator 104

superconductor = 1024

Question 4

Bands

Answer 4

N infinity energy levels
no longer discrete
continuum with maxima and minima

Question 5

Fermi Level

Answer 5

N elections, N orbitals
half full
HOMO - fermi level
LUMO - unoccupied

Question 6

Simple Metal

Answer 6

high coordination number
low ionisation energy - positive ion
core electrons shield positive
electrons move independently

Question 7

Thermal Excitation of Electrons

Answer 7

finite temperature
electrons near fermi level
excite electrons at the top of the fermi level
resistance increase with temperature
ion core neglected, appear bigger, repel more
electrons less efficient
energy dicipated as heat

Question 8

Incandescence

Answer 8

electrons collide with nuclei
energy transferred to nucleus
core electrons excited
electrons fall back down = glowing

Question 9

Nearly Free Electron Model

Answer 9

electrons attracted to the core 
energy decreases as they approach 
ion core = band gap 
filled band = insulator 
bigger band = better insulator

Question 10

Conductor

Answer 10

fermi in unoccupied, LUMO

Question 11

Insulator

Answer 11

fermi at top of valence, band gap

Question 12

Semi-Conductor

Answer 12

fermi top of valence if 0 K, small band gap

Question 13

Group 1

Answer 13

partially filled band
high density near fermi
conduction the

Question 14

Group 2

Answer 14

filled band - should be an insulator
actually conducts
s and p orbitals overlap
fermi in unoccupied, LUMO

Question 15

Superconductivity

Answer 15

electrons flow through 
attracted to ion cores, move slightly 
subsequent electrons follow first electron
Cooper pairs
increased conductivity

Question 16

Quantum Tunnelling

Answer 16

current proportional to width of wall
insulator - particles too far apart
squeezed - conducts, quantum tunnelling, current flows

Question 17

Transition Metals

Answer 17

d-orbitals highly directional, cannot use free electron model
s and d orbitals overlap
conduct - fermi in s orbital, d orbital filled

Question 18

Conjugated Planes

Answer 18

planar pi-system, bands formed 
conduct at room temperature 
0 K bad conductor, cannot excite electrons 
dope with electron donating atom
enhances conductivity 
increase density of states near fermi

Question 19

Covalent Solids

Answer 19

tetrahedral elements
s and p orbitals overlap
group 4 - gap decreases down the group

Question 20

Semiconductor Junctions

Answer 20

0 K do not conduct
temperature increases so does conductivity
doped, increases conductivity
i-type HOMO full, LUMO empty
p-type HOMO full, piece of LUMO near fermi
n-type HOMO full, piece of HOMO near LUMO

Question 21

Conducting Polymers

Answer 21

conjugated linear system 
electrons in resonance, flow
bond lengths alternate 
electrons found near close electrons 
can add dopants