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How to solve?
A substance is 20 wt% Sn and 80 wt% Au.
What are the atomic percentages of each? |
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Definition
-recall that atomic % = (atoms of X)/(total # atoms)
-assume basis of 100 g
-convert grams to moles to # atoms for each
-add to get total # atoms
-calculate atomic % |
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| Aufbau Principle of electron configuration |
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Definition
1s
2s 2p
3s 3p 3d
4s 4p 4d 4f
etc. |
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| Hund's Rules of electron configuration |
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Definition
1. Electron pairs with opposing spins are low energy
2. Electrons orbiting in the same direction are low energy
3. Make half-filled subshells when applicable |
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| Most pure elements exist as ___ |
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Definition
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| atoms with same number of protons but different numbers of neutrons |
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Definition
called: principle quantum number
symbol: n
defines: shell
related to: energy level; distance from nucleus
ex: 1, 2, 3 |
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called: angular momentum number
symbol: l
defines: subshell
related to: orbital shapes
ex: 0, 1, 2, 3 (s, p, d, f) |
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called: magnetic number
symbol: ml
defines: orbitals for e pairs within subshells
ex: 0, +1, -1, +2, -2 |
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called: spin number
symbol: ms
defines: spin
ex: + or - |
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| In transition metal ions, the relative energy levels of subshells can shift such that electrons from the ___ subshell are usually given up first. |
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describe bond types
graphite |
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Definition
strong covalent within a sheet
weak secondary bonds between sheets |
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describe bond types
Al + Si + Mg alloy |
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Definition
| it's a metal alloy, so the bonding is metallic |
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describe bond types
polyethelene |
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Definition
| it's a hydrocarbon polymer, so it has strong covelent bonding |
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describe bond types
ice (frozen water) |
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Definition
covalent intra-atomic bonds
secondary (hydrogen) inter-atomic bonds |
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| Covalent bonds are highly ___ and are characterized by sharing of electrons and relatively ___ coordination numbers. |
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Definition
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Definition
describes shape of unit cell
can completely fill space with translational symmetry
there are 7 (cubic, tetragonal, hexagonal, etc.) |
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lattice parameters
(aka lattice constants) |
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Definition
| lengths of sides a, b, c of a unit cell for a crystal system |
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arrangement of atoms in 3D
points in space that are equivalent thru translational symmetry
each may consist of more than one atom (the basis) |
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Primitive cell vs.
non-primitive cell |
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Definition
| primitive cell has only one lattice point per unit cell |
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Definition
possible arrangements of lattice points in the 7 crystal systems
there are 14 (simple cubic, fcc, bcc, etc.) |
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Definition
Bravais lattice + basis
(unit cell) (atom complex)
ex, simple cubic + atom pair = crystal structure |
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Definition
| just a location in the unit cell |
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Definition
[ ]
[(a displacement) (b disp.) (c disp.)]
use lowest whole numbers |
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family of lattice directions
(aka general direction) |
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Definition
< >
set of directions that are equivalent through symmetry |
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Definition
( )
((a intercept)-1 (b intcpt.)-1 (c intcpt.)-1)
note: of the plane inter cepts the origin,
translate it before you give the indeces |
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number of atoms per unit length/area
in a given crystal direction/plane |
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Definition
sc: a = 2r
fcc: a = 4r/rt(2)
bcc: a = 4r/rt(3)
hcp: a = 2r |
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calculate density
from unit cell |
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Definition
| density = [(# atoms)/(volume)]*[(atomic wt)/(NA)] |
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Definition
APF = (V of atoms in cell)/(V of cell)
APF = [(# atoms/cell)(4πr3/3)]/(a2)
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diffraction rules
simple cubic |
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Definition
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| h k l all odd or all even |
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applications of
X-ray diffraction |
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Definition
1. determination of crystal structure (computer-aided)
ex, DNA structure
2. determination of glassy-to-crystalline phase transitions in glassy materials
ex, take XRD at different temperatures and compare them
3. determination of crystal quality
ex, impurities make for wider peaks; the skinnier the peaks, the higher the crystal quality
4. amounts and phases present in multiphase systems |
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Definition
| number of immediate neighbors surrounding an atom |
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| Pauli exclusion principle |
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Definition
| no two electrons in an atom can have the same four quantum numbers |
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Bohr model of atom
assumptions?
limitations? |
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Definition
1. e move about nucleus in defined orbits
2. each e has quantized energy
3. transition form one state to another requires a quantized amount of energy to be absorbed or released
1. works correctly only for hydrogen |
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Definition
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ionic bond properties
bond strength?
directional bonds?
electrons?
conducting?
CNs?
ductile? |
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Definition
relatively high bond energy
(high melting points, high stiffness, low thermal expansion)
low electrical conductivity
hard + brittle
high CNs |
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covalent bond properties
bond strength?
directional bonds?
electrons?
conducting?
CNs?
ductile? |
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Definition
high directionality
relatively strong bonds (but less than ionic)
tend to be brittle
electric insulating or semi-conducting
low CNs |
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metallic bond properties
bond strength?
directional bonds?
electrons?
conducting?
CNs?
ductile?
appearance? |
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Definition
can be weak or strong bonds
non-directional bonds
delocalized electrons
good conductors
high CNs
ductile at room temp
opaque and shiny |
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Definition
amorphous or glassy
no long-range order
no periodic packing--non-dense, random packing |
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Definition
long-range order
dense, ordered packing
periodic, 3D arrays
lower energy than amorphous |
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Zachariasen Rules
glass formers |
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Definition
1. each O should be linked to no more than 2 cations
2. CN of oxygen about each cation must be small (4 or less)
3. oxygen polyhedra share corners (not edges nor faces)
4. at least 3 corners of polyhedra should be shared
cation-O bond are strong
usually cation is relatively electronegative -> less ionic character |
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| some typical glass formers |
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