Final Flashcards
What is the fundamental difference between states of matter
The fundamental difference between states of matter is the distance between particles.
What is the order, displacement, and diffusion of solids
Solids: Ordered particles that are very close together, don’t change position, and have no diffusion.
what is the order, displacement, and diffusion of liquids
Liquids: Disordered particles that are close together, change positions and diffuse slowly.
What is the order, displacement, and diffusion of gases
Gas: Totally disordered particles that are very far apart, have lots of empty space between them, and have rapid diffusion.
What types of matter are compressible
Another characteristic is Compressibility. Solids and liquids are not compressible, applying a force can’t make them take up less space. However gases can be compressed into a smaller container.
What are the two antagonistic entities that determine the state of matter for a substance
The state of a substance at a particular temperature and pressure depends on two antagonistic entities:
- Attraction between particles: which acts to draw particles together
- The kinetic energy of the particles: which rises with temperature and acts to separate particles.
How stronger and intermolecular forces
The attraction between molecules are not nearly as strong as the chemical bonds that hold compounds together.
But it does control physical properties such as boiling and melting points, viscosity and vapour pressure.
What is the difference between intermolecular and intramolecular forces
Intermolecular forces = between molecules
Intramolecular forces = inside a molecule
what are the fundamental different types of particles that have intermolecular forces
The strength of an intermolecular force depends on whether or not the species are polar molecules, non-polar molecules, atoms, or ions.
How does polarity or change influence the strength of attraction
The more polar the molecule or highly charged the ion, the stronger the attraction from one species to another.
how is the intermolecular force related to distance
The intermolecular force is inversely proportional to the distance squared.
1/r^2
What are Ion-dipole interactions important
Ion-dipole interactions are an important force in solutions of ions and supramolecular chemistry. One of the strongest of the intermolecular forces because it is the attraction of a full charge for a partial charge.
What are Ion-dipole forces responsible for
these forces are responsible for ionic substance dissolving in polar solvents.
For a soluble solid, the sum of the anion-dipole and cation-dipole forces can overcome the lattice energy.
What are dipole-dipole forces
Polar molecules have permanent dipole moments. Partially negative ends of polar molecules are attracted to partially positive ends of nearby polar molecules.
Higher Dipole moment (D) usually results in higher Melting points and Boiling points.
what is hydrogen bonding
Due to an especially strong form of dipole dipole interactions called Hydrogen bonding, molecules like H$_2$O, HF, and NH$_3$ have high boiling points compared to other molecules in similar AH$_n$ forms.
The dipole-dipole interaction experienced when H is bonded to N, O or F are much stronger than other dipole-dipole interactions
Why does hydrogen bonding occur
Hydrogen bonding arises in part from the high electronegativity of N, O, and F.
When H is bonded to one of these very electronegative elements and the H nucleus is exposed.
How does Hydrogen bonding affect Ice
Ice has an open structure due to regulate hydrogen bonding which causes it to be less dense than liquid water.
What are London dispersion forces
All atoms and molecules are weakly attracted to one another through London dispersion forces, the attraction of an instantaneous dipole for an induced dipole.
Why do London dispersion forces occur
For an instant in time, electrons can be asymmetrically arranged around the nucleus such that the atom is polarized in that instant.
The instantaneous dipole induce a dipole in a neighbouring atom, causing mutual attraction.
Why kinds of molecules have London dispersion forces
London dispersion forces are present in all molecules, whether they are polar or non-polar.
How does size impact LDFs
London dispersion forces tend to increase in tandem with the size of an atom or molecule. bigger molecule = more electrons = more opportunities for instantaneous dipoles.
How does shape affect LDFs
The shape of the molecule affects the strength of dispersion forces:
Long, skinny molecules have stronger dispersion forces than short broad ones.
What type of force is present in situations where both polar molecules and ions are present
Ion-dipole forces
What type of force is present in situations where only ions are present
Ionic bonding forces
What type of force controls attraction when there are no ions or polar molecules
Dispersion forces
What type of force controls attraction when there are dipole but no H atoms bonded to N, O, or F atoms
Dipole-Dipole
What type of bonding controls attraction when H atoms are bonded to N, O, or F atoms
Hydrogen bonding
What is the order of bond strength in similar systems
Ionic bonding > Ion-Dipole forces > Hydrogen Bonding > Dipole-Dipole forces > Dispersion forces only
What balance affects the properties of a liquid
The properties of a given liquid depend on the balance between the
- kinetic energy of particles
- intermolecular attraction forces between particles
What is Viscosity
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.
What makes a liquid more viscous
Liquids are more viscous when their constituent molecules:
- have stronger intermolecular forces
- are easily entangled
- have higher molecular weight
What is surface tension
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.
What are Cohesive forces, and Adhesive forces
Cohesive force: binds liquid molecules to each other.
Adhesive force: binds liquid molecules to the surface.
what makes a concave surface
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.
what makes a convex surface
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.
what is Capillary action
Capillary action: strong adhesive forces draw liquid along sides of tubes and pores, cohesive forces pull along the rest of the liquid.
When does Evaporation occur
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.
What happens in an Open vs Closed system
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.
When does Vapour pressure and Vaporization increase
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.
what is Vaporization
Vaporization: Molecules escape the surface of the liquid into the gas phase.
When does boiling occur
Boiling occurs when vapour pressure = external pressure.
Normal boiling point: Temperature at which the liquids vapour pressure is 1 atmosphere (760mm Hg).
what are Volatile liquids
Volatile liquids evaporate easily and have a high vapour pressure at room temp.
what are phase changes
Changes in physical state, with no change in composition. Each phase change involves a change in the energy of the system.
What are Phase diagrams
Phase diagrams plot states of matter as a function of pressure and temperature.
what can happen at low pressures
At low pressures gases can directly change to solids. And vice versa. Solid → Gas = Sublimation. Gas → Solid = Deposition
what is a triple point
At a certain temp+pressure there is a “triple point”, where the condensing+Boiling line, Melting+freezing line, and Sublimation+Deposition line connect.
what happens after the triple point
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.
what is supercritical fluid
A Supercritical fluid has properties intermediate between a liquid and a gas.
what is unique about water
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
What are liquid crystals
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.
What is cholesteryl benzoate
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).
what are liquid crystals like
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.
what three mains forms can liquid crystals exist in
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.
how does particle position play into solids
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
what are Molecular solids
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.
What are Metallic solids
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.
What are Ionic solids
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.
what are covalent-network solids
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.
what are the arrangement of Carbon atoms in diamond and graphite
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.
what are crystalline solids
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)
what are atomic solids
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
what are insulators
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.
What are semi-conductors
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.
what are the average amounts of valence electrons in Inorganic semiconductors and what is doping
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.
what two types of semi conductor are made from doping
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
what is silicon used for
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
what are solar energy cells
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.
what are LEDs
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.
What are OLEDs
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.
what are polymers
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.
what is Polyglucose, what is Chitin
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.
how Is Febreze made
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.
What is Lignin
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
What is Bakelite
Bakelite, the first commercial plastic, is a phenolic resin.
what is addition polymerization
Many synthetic polymers have a backbone of C-C bonds.
Ex: bunch of ethenes = polyethylene.
Coupling of monomers through multiple bonds is addition polymerization.
what is HDPE
High density polyethylene (HDPE): bottles, grocery bags, milk jugs, recycling bins, playground equipment. (2)
what is PVC
Polyvinyl chloride (PVC): Pipe, window profile, siding, fencing, lawn chairs, non-food bottles. (3)
what is LDPE
Low density polyethylene (LDPE): Plastic bags, various containers, dispensing bottles, tubing. (4)
what is PP
Polypropylene (PP): Auto parts, Industrial fibres, food containers, dish ware. (5)
what is PS
Polystyrene (PS): Cafeteria trays, plastic utensils, coffee cup lids, toys, clamshell containers, packaging. (6)
How are addition polymers formed
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.
Why are polymers hard to depolymerize
Because σ bonds are stronger than π bonds, addition polymers are hard to depolymerize
what are plastics
Plastics are polymeric materials that can be formed into various shapes, usually with heat and pressure.
what are thermoplastics
Thermoplastic materials can be reshaped (e.g. polyethylene)
what are thermosetting plastics
Thermosetting plastic materials are shaped by an irreversible process (cannot be reshaped by melting and resolidifying)
what is condensation polymerization
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
what are copolymers
Polymers that are formed by two different monomers are called copolymers
what are proteins
Proteins are formed of amino acid monomers (which contain both amine and carboxylic functional groups).
how many amino acids are there
There are hundreds of amino acids known, though only 22 appear in the genetic code.
what does the structure of amino acids allow them to form
One amino acid has both functional groups needed for a condensation reaction: can build a chain
what does a chain of condensed amino acids form
A chain of condensed amino acids forms a polypeptide: that sequence will fold to form a protein
what materials are polymeric proteins
Some natural materials are polymeric proteins, such as collagen (cartilage, tendons, skin), Keratin (nails, feathers, hair, scales), and fibroin (silk, spider thread).
what can chemists make with amide linkages
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
what do most synthetic and natural polymers consist of
Synthetic and natural polymers commonly consist of a collection of macromolecules of different molecular weights.
what two regions of polymers usually have
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.
what does mass affect in polymers
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.
what do additives do
Polymeric properties may be modified by additives with lower molecular mass.
what do plasticizers do
Plasticizers decrease interactions between chains and make polymers more pliable.
what factors affect polymer properties
Factors that affect polymer properties include molecular properties, additives, and fabrication. Stretching or extruding a polymer can increase crystallinity.
what makes a polymer more rigid
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)
what is vulcanized rubber
Volcanized rubber is more elastic and less reactive than natural rubber.
how does Cross-linking affect natural polymers
Cross-linking of natural polymers make them harder, for example, the keratin in hair has less cross-linkage (disulphide bridges) than in finger nails.
what 9 factors affect polymer properties
- chain length
- branching
- polar groups
- cross-linking
- Double bonds, aromatic rings
- substituents
- Stereochemistry
- Fabrication
- Additives
what makes something a nanomaterial
Nano = 10^-^9 nanomaterials have dimensions of 1-100 nm
what are Nanoscale Semiconductors:
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.
what are Nanoscale metals
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.
what are Carbon Nanotubes
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”
What is Graphene
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.
