MATSE 201: Exam 1 Review – Flashcards
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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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| -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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| 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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| 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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| E = h? |
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| c = ?? |
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| Most pure elements exist as ___ |
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| metals |
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| isotopes |
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| atoms with same number of protons but different numbers of neutrons |
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| quantum number 1 |
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| called: principle quantum number symbol: n defines: shell related to: energy level; distance from nucleus ex: 1, 2, 3 |
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| quantum number 2 |
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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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| quantum number 3 |
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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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| quantum number 4 |
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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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| s |
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| describe bond types graphite |
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| 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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| it's a metal alloy, so the bonding is metallic |
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| describe bond types polyethelene |
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| 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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| 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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| directional low |
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| crystal system |
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| 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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| lengths of sides a, b, c of a unit cell for a crystal system |
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| lattice points |
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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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| primitive cell has only one lattice point per unit cell |
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| Bravais Lattices |
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| possible arrangements of lattice points in the 7 crystal systems there are 14 (simple cubic, fcc, bcc, etc.) |
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| crystal structure |
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| Bravais lattice + basis (unit cell) (atom complex) ex, simple cubic + atom pair = crystal structure |
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| lattice position |
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| just a location in the unit cell |
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| lattice direction |
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| [ ] [(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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set of directions that are equivalent through symmetry |
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| lattice planes |
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( ) ((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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| family of lattice planes |
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| { } |
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| linear/planar density |
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| number of atoms per unit length/area in a given crystal direction/plane |
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| a vs. r |
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| 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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| density = [(# atoms)/(volume)]*[(atomic wt)/(NA)] |
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| APF atomic packing factor |
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APF = (V of atoms in cell)/(V of cell)
APF = [(# atoms/cell)(4?r3/3)]/(a2)
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| diffraction rules simple cubic |
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| any h k l |
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| diffraction rules fcc |
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| h k l all odd or all even |
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| Bragg's Law |
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| ? = 2dhklsin? |
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| lattice plane distance |
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| dhkl= a/rt(h2+k2+l2) |
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| applications of X-ray diffraction |
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| 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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| coordination number |
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| number of immediate neighbors surrounding an atom |
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| Pauli exclusion principle |
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| 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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| 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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| bond energy vs. distance |
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| [image] |
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| ionic bond properties bond strength? directional bonds? electrons? conducting? CNs? ductile? |
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| 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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| 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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| 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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| non-crystallinity |
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| amorphous or glassy no long-range order no periodic packing--non-dense, random packing |
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| crystallinity |
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| 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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| 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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| SiO2 B2O3 GeO P2O5 As2O3 |
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| diffraction rules bcc |
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| h+k+l = even |
