Final Flashcards

Question

What type of force controls attraction when there are no ions or polar molecules

Answer 1

Dispersion forces

Answer 2

Dipole-Dipole

Answer 3

Hydrogen bonding

Answer 4

Ionic bonding > Ion-Dipole forces > Hydrogen Bonding > Dipole-Dipole forces > Dispersion forces only

Answer 5

The properties of a given liquid depend on the balance between the - kinetic energy of particles - intermolecular attraction forces between particles

Answer 6

resistance to flow. Units = Pas = Kg/ms Measured by how long it takes a steel ball to drop through a liquid over a specified distanced.

Answer 7

Liquids are more viscous when their constituent molecules: - have stronger intermolecular forces - are easily entangled - have higher molecular weight

Answer 8

Created by Imbalance of forces at the top of a liquid. Surface tension is related to the work require to increase surface area by a unit amount. Units = J/m$^2$ Bugs can float on water because the molecules on the surface assemble more tightly as they form fewer but stronger hydrogen bonds with the water molecules in the bulk.

Answer 9

**Cohesive force**: binds liquid molecules to each other. **Adhesive force**: binds liquid molecules to the surface.

Answer 10

When the adhesive forces are stronger than the cohesive forces, the liquid forms a concave surface in the container. Ex water in a graduated cylinder.

Answer 11

When the Cohesive forces are stronger than the Adhesive forces, the liquid forces a convex surface in the container. Ex mercury in a graduated cylinder.

Answer 12

Capillary action: strong adhesive forces draw liquid along sides of tubes and pores, cohesive forces pull along the rest of the liquid.

Answer 13

Evaporation occurs when energetic molecules or atoms near the surface of the liquid exceed the intermolecular forces to transition form the liquid to gas phase. The ease with which this happens dictates both the boiling point and the vapour pressure of the liquid.

Answer 14

In an Open system the molecules evaporate and are removed. In a Closed system the molecules are evaporating and condensing at the rate in equilibrium.

Answer 15

Vapour pressure increases with temperature. Vaporization is greater when the temperature is higher, the surface area is greater, or when the intermolecular forces are weaker.

Answer 16

Vaporization: Molecules escape the surface of the liquid into the gas phase.

Answer 17

Boiling occurs when vapour pressure = external pressure. Normal boiling point: Temperature at which the liquids vapour pressure is 1 atmosphere (760mm Hg).

Answer 18

Volatile liquids evaporate easily and have a high vapour pressure at room temp.

Answer 19

Changes in physical state, with no change in composition. Each phase change involves a change in the energy of the system.

Answer 20

Phase diagrams plot states of matter as a function of pressure and temperature.

Answer 21

At low pressures gases can directly change to solids. And vice versa. Solid → Gas = Sublimation. Gas → Solid = Deposition

Answer 22

At a certain temp+pressure there is a “triple point”, where the condensing+Boiling line, Melting+freezing line, and Sublimation+Deposition line connect.

Answer 23

After the triple point there is a line where liquid turns to solid and vice versa. There is also a gas←→ liquid line that eventually ends in an area where matter is considered a supercritical fluid.

Answer 24

A Supercritical fluid has properties intermediate between a liquid and a gas.

Answer 25

Water shows an unusual behaviour trend at the solid liquid transition. For one thing, solid is less dense than liquid. And at higher pressure, water freezes and melts and lower temperature (the opposite of most materials where temp increases with pressure. Waters Triple point is 272 K 101 kPa and its critical point is 647 K and 22 MPa

Answer 26

Solids are characterized by their order, and Liquids are characterized by their lack of order. Liquid Crystals are substances that exhibit one of more ordered phases at a temperature above the melting point.

Answer 27

The first systematic report of a liquid crystal was cholesteryl benzoate (in 1888). At temperatures lower than 145º = solid, 145-179º = opaque liquid (Liquid Crystals), above 179º = clear liquid. Cholesteryl benzoate passes through an intermediate liquid crystalline phase. It has some properties of liquids and some of solids. The liquid flows (liquid property) but has some order (solid property).

Answer 28

Liquid Crystal molecules are usually long and rod-like. In normal liquid phases they are randomly oriented. In the liquid crystal form molecules have some order, but not as much as solids.

Answer 29

Can exist in three main forms: - Nematic Liquid Crystals - are ordered along the long axis of the molecule only. - Smectic Liquid Crystals - are ordered along the long axis of the molecule and in one other dimension. - Cholesteric Liquid Crystals - are ordered along the long axis of the molecule and in twister layers.

Answer 30

In solids, the intermolecular forces are strong enough to lock particles into fixed positions. - Crystalline solids have the particles arranged in a regular repeating patter. Ex metals, minerals, etc - Amorphous solids have those particles randomly arranged. Ex glass, wax, etc

Answer 31

Molecular solids are atoms or molecules held together by intermolecular forces. They are usually soft and have low melting points and low thermal and electrical conductivity. Efficient packing of molecules is important (since they are not regular spheres). For example Benzene has a high melting point due to efficient packing.

Answer 32

Consist entirely of metal atoms; metallic bonding. Valence electrons delocalized throughout the solid allow metallic solids to be good conductors of both heat and electricity. Metals can vary greatly in the strength of the bonding due to band theory.

Answer 33

Consist of ions held together by ionic bonds (i.e by electrostatic forces of attraction) They are hard, brittle, and have high melting points. The larger the charges (Q$_1$,Q$_2$) and the smaller the distance (r) between ions, the stronger the ionic bonding The structure of the ionic solid depends on the charges on the ions and on the relative sizes of ions.

Answer 34

Consist of atoms held together, in large networks or chains, with covalent bonds. Have much higher melting points and are much harder than molecular solids. Strong covalent bonds connect the atoms.

Answer 35

each C atom is tetrahedral in a 3D array of atoms. This is why diamond is so hard and has a high melting point (3550ºC) Strong covalent bonds connect the atoms within the layers of graphite. C-C 1.42 A. The layers are held together by weak dispersion forces 3.35 A. graphite is a good lubricant.

Answer 36

Crystalline solids include: Molecular solids: units are molecules, low melting point. Ex Iodine Ionic solids: units are Cations and Anions, high melting point. Ex Calcite (CaCO3)

Answer 37

Nonbonding: held together by dispersion forces, low melting point. Ex Xenone Metallic: held together by metallic bonds, low melting point. Ex Gold Network Covalent: held together by constant bonds, high melting point. Ex quartz

Answer 38

Many non-metals are insulators, i.e. electrons can’t flow freely through them. Insulators are characterized by having a large band gap (energy difference between a filled band and an empty band). Example include glass, air, rubber, wood, most plastics. Ceramics are usually insulators, but some copper oxides are superconductors.

Answer 39

Silicon has the same structure as diamond, but a much smaller band gap: Small enough that high temperatures or IR radiation can be enough to promote electrons from one band to another. In a semiconductor the lower band is the Valence band, and the top one is the conduction band. Usually some electrons much be promoted to the conduction band to work as a conductor.

Answer 40

Inorganic compounds that are semiconductors tend to have an average of 4 valence electrons, and their conductivity may be increased by doping. → addition of controlled amount of an impurity to move away from average of 4 electrons. Ex a tiny bit of gallium added to silicon.

Answer 41

Doping yields different kinds of semiconductors: n-type - Dopant atom has more valence electrons than the host atom - adds electrons to the conduction band p-type - Dopant atom has fewer valence electrons than the host atom - leads to holes in the valence band

Answer 42

Many modern devices rely on silicon wafers or “chips” containing complex patterns of semiconductors, insulators, and metal wires. - Si is abundant, cheap, and can grow enormous amounts of perfect crystals - It is non toxic - and can be chemically protected by SiO2

Answer 43

Semiconductors are also used in the production of solar energy cells. If you shine light with an appropriate wavelength on a semiconductor, electrons are promoted to the conduction band, making the material more conductive. This is a property known as photoconductivity. Solar cells are formed by joining n-type and p-type semiconductors. Electrons are promoted by photons, generating a current.

Answer 44

Light-emitting diodes (LEDs) are used in many types of displays. the mechanism of action is the opposite of that involved in solar cells. A voltage is applied and electrons in the conduction from the n-side combine at the junction with the holes from the p-side. Light is emitted whose photons have energy equal to the band gap.

Answer 45

Organic LEDs (OLEDs) have some advantages over traditional LEDs. Lighter, more flexible, and may be brighter and more energy efficient, made from conducting organic polymers. Some problems with lifetime of devices, especially for blue (higher E) Enabled the creation of curved and flexible displays.

Answer 46

Many everyday materials are polymeric, involving simple organic molecules called monomers linked together to make chains, rings, networks, and folded constructrs. For example, cellulose is a polysaccharide (”polysugar”) chain of repeating glucose molecules.

Answer 47

Polyglucose makes paper, and cotton. If the related glucose unit has an amide group attached to it, the resulting polymer is called chitin. Insect and crustacean exoskeletons are composite materials of chitin and calcium carbonate.

Answer 48

Humans have also used polysaccharides in imaginative ways. The air freshener Febreze contains a cyclic sugar called cyclodextrin, a ring shaped molecule that captures odor molecules.

Answer 49

Lignin is a polyphenolic crosslinked polymer found in wood. Small lignin molecules are called tannins. Lignin is rigid and resistant to rot complex cross-linked structure

Answer 50

Bakelite, the first commercial plastic, is a phenolic resin.

Answer 51

Many synthetic polymers have a backbone of C-C bonds. Ex: bunch of ethenes = polyethylene. Coupling of monomers through multiple bonds is addition polymerization.

Answer 52

High density polyethylene (HDPE): bottles, grocery bags, milk jugs, recycling bins, playground equipment. (2)

Answer 53

Polyvinyl chloride (PVC): Pipe, window profile, siding, fencing, lawn chairs, non-food bottles. (3)

Answer 54

Low density polyethylene (LDPE): Plastic bags, various containers, dispensing bottles, tubing. (4)

Answer 55

Polypropylene (PP): Auto parts, Industrial fibres, food containers, dish ware. (5)

Answer 56

Polystyrene (PS): Cafeteria trays, plastic utensils, coffee cup lids, toys, clamshell containers, packaging. (6)

Answer 57

Addition polymers are formed by breaking the C=C π bond and forming a new C-C σ bond between the monomer and the polymer chain.

Answer 58

Because σ bonds are stronger than π bonds, addition polymers are hard to depolymerize

Answer 59

Plastics are polymeric materials that can be formed into various shapes, usually with heat and pressure.

Answer 60

Thermoplastic materials can be reshaped (e.g. polyethylene)

Answer 61

Thermosetting plastic materials are shaped by an irreversible process (cannot be reshaped by melting and resolidifying)

Answer 62

Condensation Polymerization: two molecules are joined to form a larger molecule by the elimination of a small molecule. e.g. water, methanol, acetic acid ex: amine + carboxylic acid → amide + water

Answer 63

Polymers that are formed by two different monomers are called copolymers

Answer 64

Proteins are formed of amino acid monomers (which contain both amine and carboxylic functional groups).

Answer 65

There are hundreds of amino acids known, though only 22 appear in the genetic code.

Answer 66

One amino acid has both functional groups needed for a condensation reaction: can build a chain

Answer 67

A chain of condensed amino acids forms a polypeptide: that sequence will fold to form a protein

Answer 68

Some natural materials are polymeric proteins, such as collagen (cartilage, tendons, skin), Keratin (nails, feathers, hair, scales), and fibroin (silk, spider thread).

Answer 69

Chemists also make polymers using amide linkages. Nylon was the first synthetic condensation polymer discovered, and other soon followed based on ester linkages. Ex: Nylon 6 making clothing and string, Polyester Dacron making soda bottles, and clothing, and Lexan making bulletproof glass, safety glasses, and DVDs

Answer 70

Synthetic and natural polymers commonly consist of a collection of macromolecules of different molecular weights.

Answer 71

Intermolecular forces between chains give order to polymers, crystallinity is order. These kinds of polymers often have a crystalline region of order when the chains are all staked, and amorphous regions of disorder when the chains are random.

Answer 72

Intermolecular forces between chains give order to polymers, crystallinity is order. These kinds of polymers often have a crystalline region of order when the chains are all staked, and amorphous regions of disorder when the chains are random.

Answer 73

Polymeric properties may be modified by additives with lower molecular mass.

Answer 74

Plasticizers decrease interactions between chains and make polymers more pliable.

Answer 75

Factors that affect polymer properties include molecular properties, additives, and fabrication. Stretching or extruding a polymer can increase crystallinity.

Answer 76

Cross-linked polymers are more rigid than straight-chain polymers: e.g. vulcanization of natural rubber involves crosslinking of an unsaturated polymer with sulphur (S_8)

Answer 77

Volcanized rubber is more elastic and less reactive than natural rubber.

Answer 78

Cross-linking of natural polymers make them harder, for example, the keratin in hair has less cross-linkage (disulphide bridges) than in finger nails.

Answer 79

- chain length - branching - polar groups - cross-linking - Double bonds, aromatic rings - substituents - Stereochemistry - Fabrication - Additives

Answer 80

Nano = 10^-^9 nanomaterials have dimensions of 1-100 nm

Answer 81

Semiconductor particles with 1-10 nm diameters are called quantum dots. Band gaps change substantially with size in this range. Fluorescent CdSe Quantum dots: Increasing particle size and decreasing band gap leads to more red.

Answer 82

metals in the 1-100 nm size range are interesting nano-materials - known for centuries that finely divided metals have strange properties. - Medieval craftsmen dispersed preciously metals in molten glass to make deep reds and yellow colours.

Answer 83

Carbon Nanotubes: Sheets of graphite rolled up and capped at one or both ends. - 1000s of nm long but only 1nm wide - Single-walled and multi-walled tubes - interesting electronic and structural (mechanically very strong) properties - promising for use as “nanowires”

Answer 84

Graphene: A single unrolled sheet of graphite - made from peeling single sheets from graphite using scotch tape - A “semi-metal” with record thermal conductivity - Can sustain current densities 6 times that of copper.