Intermolecular Forces, Liquids, Solids and Materials Flashcards
Solids
Ordered, particles do not change position, close together, no diffusion, incompressible.
Liquids
Some disorder, particles move, close together, slow diffusion, incompressible.
Gas
Total disorders, empty space, rapid diffusion, compressible.
Kinetic Energy
The kinetic energy of a particle is temperature depended and keeps particles separated. One of the factors that changes states of a substance. Higher kinetic energy over powers intermolecular forces, causing them to break (gases.)
Strength of attraction
The strength of attraction between particles draws particles together. Higher the attraction, the stronger the intermolecular forces.
Intermolecular forces (van der Waals)
Strength depends on polarity. More polar or highly charged = stronger the attraction. Larger molecules have more intermolecular forces
Ion-dipole forces
Attraction of a full charge to a partial charge, in soluble solids, anion and cation dipole moments cancel out the lattice energy (dissolve). Responsible for ionic substances dissolving in polar solvents.
Dipole-dipole forces
Partial neg and pos ends on polar molecules are attracted to each other. Increases with electronegativity.
Hydrogen bonding
Strongest dipole bond, occurs when a hydrogen molecule bonds to a highly electronegative molecule - F, N, O and the nucleus is consequentially exposed.
Water properites
Very strong H-bonding (2 bonds). Has stronger bonding in its liquid form because molecules can move to fill empty space. The density of ice is lower because of empty spaces in the bonding structure.
London Dispersion forces
Present in all molecules, more so in larger ones. Attraction of an instantaneous dipole to an induced dipole. Electrons are asymmetrically arranged around the nucleus, making the atom slightly polarized. Long, skinny molecules have stronger dispersion forces than short, broad ones.
Boiling point
Increases with molecular weight and electronegativity. Occurs when vapour pressure is equal to the external pressure. The normal boiling point is the temperature when the liquid’s vapour pressures is 1 atm.
Melting point
Increases with electronegativity and efficient packing of molecules.
Order of intermolecular forces
Ionic > covalent > ion-dipole > H-bonds > dipole-dipole > dispersion
Liquids
Properties depend on a balance between kinetic energy and intermolecular attractive forces.
Viscosity
Resistance to flow, increases with stronger intermolecular forces, higher molecular weights and molecules that get easily entangled.
Surface tension
Created by an imbalance of forces at the top of a liquid. Related to the work required to increase surface area by a unit amount and interfacial behavior.
Interfacial behavior
Cohesive and adhesive forces.
Cohesive forces
Binds molecules to one another
Adhesive forces
Binds molecules to the surface
Concave surface
Adhesive forces > cohesive forces. ex) water
Convex surface
Cohesive forces > adhesive forces ex) mercury
Capillary action
Strong adhesive forces draw liquid along the sides of tubes and pores, cohesive forces pull along the rest of the liquid.
Evaporation
When energetic molecules/atoms near the surface of a liquid exceed intermolecular forces to transition from liquid to gas. Ease of this dictates boiling point and vapour pressure.
Open system
Molecules evaporate and are removed
Closed system
Molecules evaporate and condense at the same rate (equillibrium)
Vapour pressure
Increases with temperature and thus increases with kinetic energy and decreases with stronger intermolecular forces.
Vapourization
When molecules escape the surface of the liquid into a gas, increases with temperature (kinetic energy, low boiling point) and surface area. Decreases with strong intermolecular forces.
Volatile liquids
Evaporate easily, have high vapour pressure at room temperature.
Phase changes
Changes in a physical state with no change in composition. Involves energy changes.
Phase diagrams
Plot changes in matter states as a function of pressure and temperature.
Deposition
Change from gas to solid
Sublimation
Change from solid to gas
Freezing
Change from liquid to solid
Melting
Change from solid to liquid
Condensing
Change from gas to liquid
Boiling
Change from liquid to gas
Supercritical fluid
Has properties between a liquid and a gas
Triple point
A point where the temperature and pressure allows all three matter states to exist in equilibrium.
Critical point
Transition to supercritical fluid
Liquid Crystals
Have some order. Exhibit one or more ordered phases at a temperature above the melting point. Long and rod-like, normal liquid phases are randomly oriented.
Nematic crystals
Ordered along the long axis
Smectic
Ordered along the long axis and in another dimension
Cholesteric
Ordered along the long axis of the molecule and twisted in layers
Solids
Intermolecular forces are strong enough to lock particles in fixed positions.
Crystalline solids
Particles arranged in a repeating pattern - metals, minerals
Amorphous solids
Randomly arranged particles - glass, wax.
Molecular solids
Atoms or molecules held together by intermolecular forces. Usually soft, low melting points, low thermal and electrical conductivity. Efficient packing of molecules is important.
Metallic solides
Metallic bonding, conduct electricity, made of metal atoms. Valence electrons are delocalized throughout the solid, vary greatly in bond strength - best described via band theory.
Ionic solids
Ions held together by ionic bonds. Larger the charges and smaller the distance on the periodic table, stronger the ionic bonds. They are hard, brittle and have high melting points. Structure depends on charges on the ions and sizes.
Covalent network solids
Atoms held together in large network of chains with strong covalent bonds. Have higher melting points and are much harder than molecular solids. 3D array of solids. Sometimes layers (ie. graphite) are held together with weak dispersion forces.
Semiconductors
Inorganic compounds that are semiconductors (silicon) have average 4 valence electrons and conductivity can be increased via doping.
Doping
Addition of controlled amounts of a second element to a semiconductor. Dopant is usually the 2nd element added.
N-type semiconductors
Addition of electrons to the conduction band. Dopant atom has more valence electrons than the host atom.
P-type semiconductors
Subtraction of electrons, which leads to holes in the valence band. Dopant atom has less valence electrons that the host atom.
Solar energy cells
Produced from semiconductors. Light (photons) shone at the appropriate wavelength promotes electrons to the conduction band and make the material more conductive - generates a current. Formed from n-type and p-type semiconductors in the same direction.
Photoconductivity
Electrons are promoted by photons to generate a current and make the material more conductive.
Light-emitting diodes (LEDs)
Opposite of solar cells, voltage is applied to electrons in the conduction band from the n-side to combine with the holes on the p-side. So n-type and p-type are facing each other. Light is emitted when the photons have energy equal to the band gap.
Polymers
Involve simple molecules (monomers) linked together to make chains, rings, networks and folded constructs. Attracted to each other by variety of covalent and intermolecular forces.
Cellulose
Polysaccharide chain made of repeating glucose molecules. Found in cotton and paper.
Chitin
Repeating glucose unit with an attached amide group. Found in insects and crustaceans.
Cyclodextrin
Ring-shaped molecule that captures odor molecules
Lignin
Polymer in wood that is resistant to rot, has a complex cross-linked structure.
Tannins
Small lignin molecules
Bakelite
First commercial plastic made of phenolic resin
Addition polymerization
The coupling of monomers through multiple bonds. Formed by breaking the double carbon pi bond and forming a new carbon sigma bond between the monomer and polymer chain. Hard to depolymerize because sigma bonds are stronger than pi bonds.
Synthetic polymers
Have a backbone of C-C bonds.
Plastics
Polymeric materials that form various shapes with heat and pressure
Themoplastics
Materials can be reshaped
Themosetting plastics
Materials are shaped by an irreversible process
Condensation polymerization
Two molecules are joined to form a larger molecule via the elimination of a small molecule. HOOC - X - COOH + H2N - Y - NH2 –> …X - CONH - Y…
Copolymers
Polymers formed by two different monomers
Proteins
Formed by amino acid monomers that contain amines and carboxylic functional groups.
Polypeptide
Chain of condensed amino acids that fold to form proteins.
Natural polymeric proteins
Collages, keratin, fibroin
Structure and physical properties of polymers
Synthetic and natural polymers commonly consist of a collection of macromolecules of different molecular weights. Intermolecular forces between chains give order to polymers.
Crystallinity
Order in polymers. Stretching or extruding a polymer can increase it. Strongly influenced by average molecular mass.
Factors that affect polymer properties
Chain length, branching, polar groups, cross-linking, double bonds, aromatic rings, substituents, stereochemistry (chirality), fabrication, additives.
Plasticizers
Decrease interactions between chains of polymers and makes them pliable.
Cross-linked polymers
Crosslinking of natural polymers makes them harder (keratin).
Vulcanized rubber
More elastic and less reactive than natural rubber due to crosslinking with an unsaturated polymer of sulfur. More rigid than straight chain polymers.
Nanomaterials
Quantum dots, some metals, carbon nanotubes, graphene
Nanoscale semiconductors
Semiconductor particles with 1-10nm diameters. Band gaps change substantially with size in this range.
Quantum dots
Nanoscale semiconductors. Colour is dependent on band gap in the semiconductor. As particles get larger, the colour moves to red. As band gap gets smaller, the colour moves to red. Vice versa is purple. (More energy and shorter wavelength = small particles big band gap. Less energy and larger wavelengths = large particles and small band gap.)
Nanoscale metals
Used in stained glass
Carbon nanotubes
Sheets of graphite rolled up and capped at one or both ends. Very long but only 1nm wide. Can be single or multi-walled. Used in nanowires and are mechanically very strong.
