MOLECULES AND MATERIALS Flashcards
three forms of the element carbon
Graphite, diamond, and fullerenes
___________ was named buckminsterfullerene due to its resemblance to geodesic domes
popularized by the architect ___________
C60, Buckminster Fuller
Fullerenes were discovered in _______ in the form of C60
1985
Carbon has long been used as a material in important applications
- Diamond is used in drill bits and jewelry
- Graphite is used in pencils, as a lubricant, and as a composite material
- Applications of fullerenes and nanotubes are still being explored
are maps showing which state or phase of a compound or an element will be most stable at a given combination of pressure and temperature
Phase Diagrams
The state or phase of a compound can be manipulated by changing
the temperature and pressure of the compound
Note that pressure is shown on a
______ scale
logarithmic
are a type of fullerene that have remarkable properties
Nanotubes
What property of carbon nanotubes might lead to interesting engineering
applications?
* Resistance to reactions
* Tensile strength
* Elasticity
- Tensile strength
Atoms or molecules arrange themselves into two types of solids
Crystalline solids
Amorphous solids
Atoms or molecules that assume a regular, repeating geometric arrangement
Crystalline solids
Atoms or molecules that assume a random arrangement
Amorphous solids
in crystalline solids, it is the percentage of space occupied in a given arrangement
Packing efficiency
- The less empty space in the packing of atoms or molecules in a solid, the higher the packing efficiency
- The higher the packing efficiency, the higher the density of a solid
Two ways to maximize packing efficiency
hexagonal close-packing or hcp
cubic close-packing or ccp
the third layer can be stacked directly above the atoms in the first layer
hexagonal close-packing or hcp
if the third layer can be stacked directly above the hollows in the first layer
cubic close-packing or ccp
is the smallest collection of atoms that displays all the features of a crystal structure
unit cell
Three types of cubic unit cells
simple cubic or sc
body-centered cubic or bcc
face-centered cubic or fcc
1/8 each of eight corner atoms
simple cubic
containing one additional atom within
body-centered cubic
with an additional ½ each of six atoms along the faces
face-centered cubic
How much does each atom at the corner of a cubic unit cell contribute to that
unit cell?
* 1 atom
* 1/4 atom
* 1/8 atom
* 1/12 atom
1/8 atom
Calculation of Packing Efficiency
fcc = 1/2 (# of fc) + 1/8 (# of corner) = 4
bcc = (# of bcc) - 1/8 (# of corner) = 2
sc = 1/8 (# of corner) = 1
is the number of atoms immediately adjacent to any given atom
Coordination number
Condensed Phases—Solids
- Simple cubic structure has a coordination number of __
- Body-centered cubic structure has a coordination number of __
- Close-packed structures, ccp and hcp, have coordination numbers of __
6, 8, 12
are the attractive and repulsive forces between molecules
Intermolecular forces
responsible for determining the structure and properties of condensed phases
Intermolecular forces
are common to all molecules
Dispersion forces
Dispersion forces are also called
London Forces
Dispersion forces are also referred as
instantaneous dipole–induced dipole forces
exist for two oppositely charged points separated by some distance
Dipoles
occurs when a fluctuation in electron density for an atom or molecule produces a dipole
instantaneous dipole
are short-lived and constantly forming and disappearing
Instantaneous dipoles
is created when an external electric field forces a dipole to exist
induced dipole
the source of the external electric field
permanent dipole
is a measure of how susceptible a molecule’s electron density is to perturbation by external electric fields
Polarizability
strength of a dispersion force can be estimated from
polarizability of a molecule
are the attractive and repulsive forces for molecules with a permanent dipole
Dipole–dipole forces
Molecules with larger dipoles have ________ dipole–dipole forces
stronger
Dipole–dipole forces are typically ________ than dispersion forces
stronger
are a special case of dipole–dipole forces
Hydrogen bonds
occur only in compounds containing hydrogen, which is covalently bonded to the highly electronegative elements F, O, or N
Hydrogen bonds
Intermolecular forces are ______ compared to the average covalent bond
weak
Polyethylene forms by addition polymerization. How many C-C single bonds are likely to form n C=C double bonds that undergo the reaction?
* n
* 2n
* 3n
2n
is the gas phase pressure of a substance in dynamic equilibrium with the pure liquid in a pure substance
Vapor Pressure
Liquids with high vapor pressures are described as
volatile
To measure the vapor pressure of a solid or a liquid, the system must reach
equilibrium
the temperature of a liquid at which its vapor pressure equals one atmospheric pressure (1 atm)
Normal boiling point
is a liquid’s response to the imbalance in attractive forces and the tendency to minimize energy
Surface Tension
have the greatest volumes with the least amount of surface area
Spherical shapes
is the result of molecules at the surface of a liquid experiencing fewer intermolecular forces than liquid molecules inside the bulk liquid
Surface tension
The interaction between a liquid and the surface of a solid depends on two
types of attractive forces
Cohesion forces
Adhesion forces
are liquid–liquid interactions
Cohesion forces
are liquid–solid interactions
Adhesion forces
The relative strengths of the two forces dictate the shape of a liquid’s
meniscus
Strong adhesion forces and weaker cohesion forces result in a
concave meniscus
Weak adhesion forces and stronger cohesion forces result in a
convex meniscus
A substance that has a low boiling point will also have a low value for which
property?
* Surface tension
* Vapor pressure
* Volatility
- Vapor pressure
are giant molecules constructed by sequentially stringing together
smaller molecules called monomers
Polymers
Monomers containing one or more double bonds undergo free radical
addition reactions to form
addition polymers
Monomers containing one or more double bonds undergo ____________ to form addition polymers
free radical addition reactions
Addition polymerization occurs through
initiation, propagation, and termination
A free radical, species with an unpaired electron, is produced
Initiation
The free radical attacks the double bond of the monomer to break the double bond, leaving a single bond
Propagation
A free radical reacts with another free radical
Termination
is a random event, not all polymer chains will have the same length
Termination
All methyl groups are arranged on the same side of the polymer chain
Isotactic
Methyl groups alternate systematically from one side of the polymer chain to the other
Syndiotactic
Methyl groups are arranged randomly along the polymer chain
Atactic
are formed when functional groups on the monomers react, linking the monomers together and producing water or another small molecule
Condensation polymers
Which engineering application is most likely to use thermoplastic polymers?
* Automobile engine
* Asphalt road construction
* Heating exhaust system
* Consumer product packaging
- Consumer product packaging
are made up of more than one type of monomer
Copolymers
are monomers arranged in a regular, alternating series
Alternating copolymers
are regions where a single monomer is repeated, interspersed with other regions where a different monomer is repeated
Block copolymers
are those where monomers are arranged randomly
Random copolymers
are those where monomers of different polymers are branched from a backbone of a different polymer
Graft copolymers
polymers melt or deform on heating
Thermoplastic
polymers maintain their shape and strength when heated
Thermosetting
are added to polymers to modify polymer properties
Additives
Conducting polymers are the subject of new materials research. What
fundamental concept is being used to help understand the prospects for
conducting polymers?
* Electronegativity
* Ionic bonding
* Resonance
* Thermosetting
- Resonance
