Constructive and Destructure Interference
What is Braggs law
Constructive: when 2 waves with crests and troughs perfectly align (2x amplitude)
Destructive: When two waves with crests that alighn with troughs (0 amplitude)
d=nlanda/2sintheta
d=distance, n is positive integer in moles, theta is angle of incidence, landa is wavelenth
Unit Cell
A collection of atoms, ions, molecules that is repeating unit of a crystalline lattice
Crystalline lattice
A repitition of the unit cell
Simple Cubic
How many atoms per unit cell, CN, edge length formula, packing eff.
1 Atom, 6 CN, l=2r, 52%
body Centered cubic cell
How many atoms per unit cell, CN, edge length formula, packing eff.
2 Atoms/unit cell, 8 CN, l=4r/sqrt3, 68%
Face centered cubic cell
4 Atoms, 12 CN, 2(sqrt2)r, 74%
How many atom/unit cell is in each of the following:
Corner
Edge
Face
Body
Corner=1/8
Edge=1/4
Face=1/2
Body:1
How do you get the unit cells for Simple, BCC, FCC
Simple=(1/8)(8)
BCC= 1+ (1/8)(8)
FCC=(1/8)(8) + (1/2)(6)
What are the 2 types of stacking - which is more efficient
Direct row
Half sphere offset row- more efficient
How do you get a tetrahedral structure
Offset layer stacking of Layers B on Layer A (in between the layers)
What are the closest packed styuctures called, what are their packing efficiency, how are they layered
Wh ich one is FCC
Both have 74%
Hexagonal:ABA
Cubic: ABC
Cubic is FCC
What is the formula to get packing efficiency
(N Atom)(V atom)/V Unit cell
What is the degree of order for Solids
Amorphous-Short range
Polycrystalline-Mid range
Crystalline- long range
What are the crystalline solids
Molecular solids- molecules- low melting points
Ionic solids- Have cations and anions-high meling points
Atomic solids (units are atoms)
Nonbonding-dispersion forces- low melting pt (mainly noble gases)
Metallic- metallic bonds- variable melting pts
Network Covalent- held together by covalent bonds- high melting pt
Molecular solids
What are the composite units, melting pt, what are they held by, conduction, what are some examples
- Composite units are molecules
- Low melting pt
- Held together by IMF
- Poor conductures of heat/electricity
- Ice, Dry ice, iodine MOLECULES
What are molecular solids with different crystalline stuctures called
Polymorphs- Different polymorphs of ice is why there are different patterns of snowflakes
Ionic Solids
Composite units, where do larger/smaller ion occupy, melting pt, conduction, examples
- Composite units are formula units (cations and anions)
- Larger ions occupy lattice/smaller occupy holes in unit cell (Na+ in holes, Cl- in lattice)
- High melting pts, held together by strong ionic bonds
- Poor conductors in solid, good conductors in aqueous state
- Brittle
- CsCl, NaCl
Nonbonding
Composite units, held together by, which group, melting pt, conduction
- Composite units are individual atoms
- Held together by dispersion
- Group 8
- Low melting pts, increase with molar mass
- Poor conductors of heat amd electricity
Metallic
Composite units, melting pt, conduction, what are some cool properties
- Composite units are individual atoms (metal cations in lattice position)
- High melting pt
- Good conductors of heat and electricity in solid state
- Malleable- hammered into thin sheets
- Ductile- wires
- Layers of cations can slide over each other
Network covalent
Composite units, melting pt, conduction, how are they held
- Composite units are individual atoms
- Formed by non mentals such as (C,Si,As and its oxides or carbides)
- VERY high melting pts
- Atoms at lattice pts held together by strong covalent bonds
- Poor conductors of heat and electricity (BESIDES graphite)
What are the allotropes of Carbon
Different forms of network covalent atomic solids of elemental carbon called allotropes
Graphite: 3 valence e= for bonding,1 valence electron free to travel, weak dispersion forces
Diamind: very hard, extensive nework of covalent bonds, each C bonded to 4 other C in a tetrahedral
