Chap 12

Question 1

Lattice and a unit cells (types)

Answer 1

a regular arrangement of geometrical objects in space

A single repeating unit that can produce the lattice is called a unit cell.

• simple cubic
• Body centered unit cell
• face-centered unit cell.

Question 2

Summary of cubic unit cells structure

Answer 2

Simple cubic: 
   C.N: 6
   packing efficiency: 52%
   volume: (2r)^3
body centered cubic:
   C.N: 8 
   packing efficiency: 68%
    volume: (4r/sqrt(3))^3
face-centered cubic:
   C.N: 12
   volume: (4r/sqrt(2))^3
   packing efficiency: 74%

Question 3

Packing efficiency

Answer 3

Tells u how much atoms are packed together w/o too much gap btn them

Question 4

Closest packing and types

Answer 4

the efficient use of space minimizing empty space.

• Hexagonal closest-packed (ABA or BAB): coordination number: 12
• Cubic closest-packed (ABC or CAB): coordination number: 12

Question 5

Band theory

Answer 5

Used to explain bonding in solid-state physics

When N atomic orbitals of same energy combine, they form N/2 bonding MOs: forming bonding MO energy band, and N/2 anti-bonding MOs: forming anit-b energy band.

In semi-conductors: the band of bonding MO is called the valence band, and the band of anti-bonding mO is called the conduction band.

Question 6

Band gap and its relation to conductivity

Answer 6

diff btn the valence band and the conduction band.

Determines if a solid conducts electricity or not. tiny gap-> more conductive, larger gap ->less conductivity bcs electrons require more energy to jump from the valence band to the conduction band.

Question 7

Doping and its types

Answer 7

process of adding impurities to a semiconductor crystal to increase its conductivity.

Because the bandgap is so small for semiconductors, doping with small amounts of impurities can dramatically increase the conductivity of the material.

n-doping: adding of electron-rich impurity (like group 5s)
p-doping: adding of electron-deficient impurity (like group 3s) resulting in electrons holes in the valence band.

p-n conjuctions: electricity only flows in one direction

Question 8

coordination number and stability

Answer 8

The higher the coordination number, the more stable the ion.

Question 9

three types of solids, their composite unites, and the type of forces that holds each together.

Answer 9

Molecular solids: composite units are molecules held together by disp, hydro-, dipole-dipole.

Ionic solids: composed of ionic substances (ions) held together by ion-ion interaction

atomic solids: composed of atoms.

• metallic: held together by metallic bonds
• non-bonding: by dispersion forces
• Network covalent: held together by covalent bonds.

Question 10

What are crystalline lattice and unit cell

Answer 10

Are composed of orderly arrangements of atoms.

A unit cell is simply the reapting part that makes up that arrangement.

Question 11

What is band

Answer 11

Band of a solid describes the range of energy levels that electrons may have within it, as well as energy levels they may have not.

Question 12

What is the difference between polymer and copolymer?

Answer 12

When a polymer is made by linking only one type of small molecule, or monomer, together, it is called a homopolymer. When two different types of monomers are joined in the same polymer chain, the polymer is called a copolymer.

Question 13

What is the coordination number?

Answer 13

the number of atoms with which an atom is in direct contact.

Question 14

condensational polymerization

Answer 14

polymers that eliminate an atom or a small group of atoms during polymerization.