TEST 1 Flashcards
Ionic bonding can be thought of as electron exchange, why?
Ionic bonding happens between two elements with high difference in electronegativity. The stronger element will take the electron from the weaker element.
What is the △EN for Ionic bonding?
> =1.7
Why is covalent bonding thought of as electron sharing?
Covalent bonding happens between two elements with low difference in electronegativity. The two particles will share electrons with each other to lower their potential energy.
What is the △EN for covalent bonding?
=< 1.7
What are dipole dipole interactions?
attraction between the polar sides of a molecule
Where are van der waals forces found?
Almost all organic liquids, solids, and gases; between chains in polymers
What is van der walls force?
attraction because of temporary dipoles between particles
Why do atoms bond?
Because it lowers energy
What happens at equilibrium separation r?
Energy (x) is a minimum and net force is 0
When is Force attractive between two atoms
when r is greater than equilibirum
When is force repulsive at equilibrium?
when r is smaller than equilibrium
what is the E at equilibrium distance r?
the atom-atom bond energy
What property can be derived from equilirbium distance r?
bond length
What property can be derived from the E at equilibrium distance R
Bond energy
What increases if E at equilibrium distance R increases?
Melting point
Do amorphous materials have higher or lower energies than crystalline materials
higher
what is a coordination number for lattice?
Number of nearest neighbors
What is a close packed plane?
Atomic planes with highest density
What is a close packed direction?
Direction where atoms touch
SC
coord#
Atom/cell
CP direction
CP plane
Lattice constant v radius
atoms in unit cell: 1
coord#: 6
Atom/cell: 1
CP direction: <100> (edge)
CP plane: {100}
Lattice constant v radius: a=2R
BCC
coord#
Atom/cell
CP direction
CP plane
Lattice constant v radius
atoms in unit cell: 1
coord#: 8
Atom/cell: 2
CP direction: <111>
CP plane: {110}
Lattice constant v radius: √3 a= 4 R
FCC
coord#
Atom/cell
CP direction
CP plane
Lattice constant v radius
atoms in unit cell: 1
coord#: 12
Atom/cell: 4
CP direction: <110>
CP plane: {111}
Lattice constant v radius: √2 a= 4 R
What is atomic packing factor?
(Volume of all atoms in unit cell)/ volume of unit cell
What is the radius ratio?
Smaller radius/ bigger radius
Zinc Blend
Neighbor config?
Lattice constant v radii
Neighbor config: tetrahedral
Lattice constant v radii: Rc +Ra = (√3/4)a
Rock Salt
Neighbor config?
Lattice constant v radii
Neighbor config: Octahedral
Lattice constant v radii: Rc +Ra = a/2
Cesium Chloride
Neighbor config?
Lattice constant v radii
Neighbor config: Cubic
Lattice constant v radii: Rc +Ra = (√3*a)/2
How to label planes with miller index
Find intercepts, take reciprocal of each intercept
what does {hkl} mean
family of pklanes
What does [hkl] mean
direction
what does hkl mean
point
what does <hkl> mean</hkl>
family of directions
What does (hkl) mean
plane
What does a system always try to do with G
minimize G
What does thermodynamics dictate
whether a certain process can happen
G driving force needs to be positive (Gscl - Gsolid= Gdriving)
What does kinetics dictate?
How fast a process can occur
Depends on kinetic barrier
Gbarrier= Gtransition-Gscl
What does it mean to be meta stable
It means for a system to not be at its lowest energy state of matter and still be stable because the kinetic barrier is so high
What is the ground state
lowest free energy state of matter
Order substances in order of volume: amorphous substance, semi amorphous substance, crystalline substance
crystalline<semi-amorphous<amorphous
What is glass transition state?
State where glass changes from rigid and glassy to soft and rubbery
What allows elastic extensions in rubber?
Large chains intertwine and entangle with each other. When the chains unravel, it allows for stretching.
Which has more energy and entropy between a random coil and extended chain
Extended chains will have lower energy and lower entropy
What is Xi in polymers?
Mole fraction of polymer having a certain mass
What is Mi in polymers
molar mass of polymer in any given section
What data can you get from PDI?
condensation polymer: PDI ~2
Addition polymer: PDI~1.5-2
Advanced methods: PDI=1.001
Can polymers be crystalline?
no, only semi crystalline
What factors affect crystallinity in polymers
slow cooling= semi crystalline
fast cooling= amorphous
difference between linear and branched polymer
linear: semi crystal
branched: amorphous
What will increase amount of amorphous regions in a material
HIgher branching
faster cooling rate
bulkier side groups
atactic chain structure (chain is random)
block copolymer with long block lengths
atactic meaning
R groups random possition
isotactic
all r groups on same side of chain
syndiotactic
r groups on alternate sides
How would you derive young’s modulus (E) from Energy vs Interatomic spacing?
E is proportional to the tangential slope at equilibrium spacing R
How would you derive CTE from E vs Interatomic spacing graph?
The width going from the minimum of E corresponds to CTE
