Ch 12 Solids and Modern Materials Flashcards
Define X-ray Crystallography
A technique allowing us to look into crystals to determine the arrangement of the atoms and measure the distances between them.
Define Crystal Lattice
The arrangement of atoms within a crystalline solid.
Define a Unit Cell
The smallest unit that shows the pattern of arrangement for all the particles. Unit cells are repeated over and over to give the macroscopic crystal structure of the solid.
How are unit cells classified
B their symmetry
What are the fundamental types of Unit Cells
1) Cubic
2) Tetragonal
3) Orthorhombic
4) Rhombohedral
5) Hexagonal
6) Monoclinic
7) Triclinic
Define Coordination Number
The number of particles each particle is in contact with.
Define Packing Efficiency
The percentage of volume in the unit cell occupied by particles. The higher the coordination number, the more efficient the particles are packed together.
What are the characteristics of a Cubic Unit Cell
1) All unit cell corners are 90 deg angles.
2) The length of all the edges are equal.
3) There are 3 types: simple cubic, body-centered cubic, and face-centered cubic.
How many atoms are in each type of SimpleCubic Unit Cell?
1) Simple - 1
2) Body-Centered - 2
3) Face-Centered - 4
What is the coordination number for each type of Cubic Unit Cell?
1) Simple Cubic: 6
2) Body-Centered: 8
3) Face-Centered: 12
What is the packing efficiency for each of the Cubic Unit Cell?
1) Simple Cubic: 52%
2) Body-Centered: 68%
3) Face-Centered: 74%
What are the 3 types of Crystalline Solids?
1) Molecular: Aka covalent solids
2) Ionic Solids: Have a charge
3) Atomic Solid: (3 types) Non-bonding, metallic, Network covalent
Only 3 elements can form hydrogen bonds. Which three?
Nitrogen
Oxygen
Fluoride
Characteristics of Molecular (covalent) Solids?
1) Composite units are made up of molecules.
2) Low melting points
3) Held together by intermolecular attractive forces - dispersion forces, dipole/dipole attractions, and H-bonds. (Weak attractive forces).
4) Some crystallize in different structures called polymorphs (important in pharmaceuticals).
Characteristics of Ionics solids.
1) Composite units are formula unit (cation and anions)
2) High melting points
3) Lattice sites are occupied by ions
What are the 3 types of Atomic Solids?
1) Non-Bonding
2) Metallic
3) Network Covalent
What are the characteristics of a Nonbonding Atomic Solid?
1) Held together by dispersion forces
2) Low melting points
3) The only monoatomic solids
What are the characteristics of Metallic Atomic Solids?
1) Held together by metallic bonds
2) Have variable melting points
3) Have high densities
4) Form closest-packed crystal structures, most are face-centered .
What are the characteristics of Network Covalent Atomic Solids?
1) Held together by Covalent bonds
2) High melting points
3) Structure restricted by geometry of bonds
4) Cannot bend, they have rigid structures
What characteristics change as a polymorph’s type number increases?
The density and stability increases as you go from type 1 to type 6. Also, the higher types of polymorphs have a higher packing efficiency.
What are three most abundant elements on the earth?
1) Oxygen
2) Silicon
3) Aluminum
Why are metals malleable?
Because metals have a lot of free flowing electrons, which create strong but flexible bonds.
Name two types of rocks by their chemical make-up.
1) SiO2
2) CaCO3 (Calcium Carbonate)
What are the characteristics of Graphite?
1) High melting point (3800 deg Celsius) because of some Covalent bonding.
2) Slippery feel because there are only dispersion forces holding the sheets together.
3) Electrical conductor
4) Thermal Insulator
5) Chemically very non-reactive
Pencil led had no lead… what is it made of
Graphite (carbon) and clay
What are the characteristics of Graphene?
1) Thinnest, strongest material known; only one atom thick
2) Transparent and completely impermeable to all substances
3) Potential to be used for faster computers, foldable touch screens, ultra thin light panels, airplanes, ships, and cars
What are the characteristics of Diamonds?
1) Very High melting point (3800 degrees Celsius).
2) Very rigid due to the tetrahedral directionality of the Covalent bonds.
3) Very hard bco strong Covalent bonds holding the atoms in position (sp3).
4) Electrical insulator and thermal conductor (opposite of carbon)
5) Chemically very non-reactive
What is a Buckministerfullerine?
Aka a Bucky ball or a fuller one. It is a soccer ball shaped cluster of 60 carbon atoms discovered in 1980s.
What are nanotubes?
Sheets of interconnected C6 rings that assume the shape of a cylinder; can be single walled tubes or multi walled tubes.
What are the characteristics of Nanotubes?
1) 100 times stronger than steel and only 1/6 as dense.
2) Used as golf clubs and bicycle frames.
Describe the atomic structure of Silicates.
One silicon and 4 oxygen atoms form a network of Covalent tetrahedral structure in which the silicon is in the middle and the four oxygen atoms are at the corners of the tetrahedron.
What are ceramics? What are their practical uses?
Ceramics are inorganic, non-metallic solids prepared from powders mixed in water, formed into the desired shape and then heated.
They are used to make bricks, tiles, pottery, dishes, and insulating elements in electrical devices.
How is glass made?
From quickly cooled silica
What are the characteristics of Glass?
1) Aka Vitreous Silica or Fused Silica
2) Hard
3) High temp resistant
4) Low thermal expansion
5) Transparent to visible and UV light
6) Expensive for most applications
What are the characteristics of Soda-Lime Glass?
1) Aka window glass
2) 70% Silica, balance of Na2O and CaCO
3) Transparent to visible light but not UV light
4) High thermal expansion
5) Less expensive but cracks under thermal shock
What are the characteristics of Bororsilicate Glass?
1) Aka as Pyrex
2) Has added boric acid (B2O3) instead of CaCO to glass mixture
3) Withstands heating and cooling cycles
What are the characteristics of Leaded glass?
1) Aka Crystals even though they are not crystals.
2) PbO mixed with SiO2
3) High refractive index - bends light more than ordinary glass.
4) Makes ringing sound when tapped.
4) Toxicity concerns - lead free crystal development.
Define the Band Theroy
A model for bonding in Atomic Solids based on molecular orbital theory in which atomic orbitals combine and become delocalized over the entire crystal.
Describe Molecular Orbitals
The structures of metals and Covalent networks Solids result in every atom’s orbitals being shared by the entire structure.
Molecular orbitals are delocalized over the entire molecule.
Define Band Theory
Stems from the Molecular Orbital Theory, with orbitals delocalized over the entire crystal.
Define Valence Band
The band of molecular orbitals
Define Conduction Band
The band of antibonding molecular orbitals
Define Band Gap
The energy gap between the valence and conduction bands
Define Conductors, Semiconductors, and Insulators.
1) Conductors - When he valence band and conduction bands are energetically continuous.
2) Semiconductors - When a small band gap exists and electrons can be be promoted from valence to conduction Band using heat or doping.
3) Insulators - When a large band gap exists, restricting electron promotion.
Name one practical example of a semiconductor in today’s world.
A diode in computers act as a semiconductor using an open/closed mechanism to allow or stop electrical current.
What are the band gaps for the following: Diamond, Silicon, Germanium, Tin, and Lead?
1) Diamond - 5.5eV (insulator)
2) Silicon - 1.11eV (semiconductor)
3) Germanium - 0.67eV (semiconductor)
4) Tin - 0.08eV (conductor)
5) Lead - 0eV (conductor)
What is Doping?
Adding impurities to a Semiconductor’s crystal to increase its conductivity.
Essentially increasing the number of electron in the conduction Band.
What is an N-Type Semiconductor?
Semiconductors doped by adding electron-rich impurities; negatively charged electrons in conduction Band. They can use group 5a elements.
What is a P-Type Semiconductor?
Semiconductors doped with an electron deficient impurity, resulting in electro jokes in the valence band. Uses group 3a elements
What is a P-N Junction?
When a P-Type Semiconductor adjoins an N-Type Semiconductor.
Electricity can flow across the p-n junction in only one direction. This is called a diode.
It allows the accumulation of electrical energy; called an amplifier.
What is a Polymer?
Very large molecules made by repeated linking together of monomers.
Natural vs Synthetic Polymers?
1) Natural Polymers are found in living organisms. I.e. starches, proteins, and DNA.
2) Synthetic Polymers are made in a lab. I.e. plastic, styrofoams, nylon rope, and plexiglass.
What is Cellulose?
Cellulose is paper, a polymer of glucose (coming from trees).
Addition Polymerization vs Condensation Polymerization?
1) Addition Polymeryzation - monomers link together without the elimination of any atoms.
2) Condensation Polymerization - Involves the elimination of an atom or a small group of atoms.
What is a Copolymer vs Dimer?
Ci
4 examples of Addition Polymers from textbook?
1) Polyethylene
2) Polypropylene
3) Polystyrene
4) Polyvinyl Chloride
Polyethylene Uses?
Films, packaging and bottles
Polypropylene uses?
Kitchenware, fibers, appliances
Polystyrene uses?
Packaging, disposable food containers, insulation
Polyvinyl Chloride uses?
Pipe fittings, clear film for meat packaging
3 examples on Condensation Polymers from Textbook?
1) Polyurethane
2) Polyethylene Terephthalate (polyester)
3) Nylon 6,6
Polyurethane uses?
Foam furniture stuffing, spray-on insulation, automotive insulation, footwear, water protective coating.
Polyethylene Terephthalate (polyester) uses?
Tire cord, magnetic tape, apparel, soda bottles
Nylon 6,6 uses?
Home furnishings, apparel, carpet fibers, fishing line, polymer blends
