Lecture 13 (Ionic and Metallic Lattices)

Question 1

What is a band?

Answer 1

A group of MOs

Question 2

What is the band theory?

Answer 2

Electrons can move into vacant MOs within the band under the influence of small energetic contributions. The electron will be delocalized over the entire metallic crystal resulting in electrical conductivity

Question 3

What does electrical conductivity mean?

Answer 3

the characteristic property of partially filled bands of MOs

Question 4

What does thermal vibrations of the nuclei produce?

Answer 4

Electrical resistance

Question 5

How is electrical resistance enhanced?

Answer 5

higher temperatures

Question 6

What is a band gap?

Answer 6

Bands can overlap or can be separated by a difference in energy

Question 7

How does the band gap work for an insulator?

Answer 7

A fully occupied band separated by the next empty band by a large band gap

Question 8

How does the band gap work for a metallic conductor?

Answer 8

A partially occupied band or an overlap between a fully occupied band and a vacant band

Question 9

What is the Fermi level?

Answer 9

the energy level of the highest occupied orbital in a metal at absolute zero

Question 10

How does the band gap work for a semiconductor?

Answer 10

A fully occupied band separated from an unoccupied band by a small band gap

Question 11

What does electric conductivity in semiconductors depend on?

Answer 11

the availability of sufficient energy for the thermal population of upper, vacant band.

Question 12

As conductivity increases, the temperature increases. True or false?

Answer 12

True

Question 13

C (diamond) is an insulator. True and False?

Answer 13

True

Question 14

α-Sn is a metallic conductor. True or false?

Answer 14

True

Question 15

What elements are intrinsic semiconductors?

Answer 15

Si and Ge

Question 16

What do Si and Ge act as?

Answer 16

charge carriers

Question 17

How are positive holes create?

Answer 17

The removal of electrons from the lower valence band. Where electrons can move, leading to the ability to conduct electricity

Question 18

What is a charge carrier in a semiconductor?

Answer 18

A positive hole or an electron that is able to conduct electricity

Question 19

Extrinsic (n and p type) semiconductors are used for?

Answer 19

Are tuned by doping with Group 13 or Group 15 elements

Question 20

What does an extrinsic semiconductor contain?

Answer 20

it contains a dopant, which is a controlled impurity

Question 21

What does doping of Si with B, Al, or Ga create?

Answer 21

An acceptor level, populated and the positive holes act as charge carriers (p-type (positive) semiconductor)

Question 22

What does doping of Si with P or As create?

Answer 22

A donor level, populated on the conduction band, acting as carge carriers (n-type (negative) semiconductor)

Question 23

What does ionic radii depend on?

Answer 23

The estimation method

Question 24

what is lattice energy?

Answer 24

It is the change in the internal energy that accompanies the formation of one mole of the solid from its constituent gas-phase ions

Question 25

What is the Coulombic (electrostatic) force?

Answer 25

The main force acting between charged particles

Question 26

What are born forces?

Answer 26

Non-coulombic, repulsive electron-electron and nucleus-nucleus interactions also arise