MIDTERM Flashcards

Question

Weiss Intercepts

Answer 1

Indexing faces: mark if/where the projection of a face will intersect axis. * infinites are 0 * 2 congruent but diff sized faces intersect axis at different points (problem) --> fixed with MILLER WEISS-MILLER 1. change to reciprocal (1/x) 2. Find common denominator and multiply through 3. Reduce fraction 4. Bar over negative numbers 5. ## Footnote WEISS: 3a2b0c= 1/3:1/2:1/0. x6 = 6/3:6/2:6/0 = (230)

Answer 2

Group of faces that are parallel to a common line. 1 face can belong to more than 1 zone.

Answer 3

Collection of faces related by symmetry. 1. Open: do not completely enclose a space. A pyramdal prism. Open space between two parallel faces. 2. Closed: completely enclose. A dipyramidal prism. Closed space betweeen 6 opposing faces of a cube | List of forms in pg 172

Answer 4

* Oxygen and Si are 74% of crust * Al, K, Fe, Ca, Na, Mg are 24% * O and Si are 67% of mantle * Mg is 23% * Only 83/118 elements avail to make xerals * Isotopes: variable neutrons in atom

Answer 5

No two electrons in an atom can have the same quantum state Quantum State: * n=position of orbit, * l=total angular momentum: distinguishes subshells w/ different shapes (n-1) (spdf), * ml=magnetic momentum (2l+1), * ms=spin each orbital can contain 2 electrons that are distinguished by their spin

Answer 6

Atoms with more PROtons (cations) give electrons to atoms with more electrons (anions: groups 16-18).

Answer 7

* **Potential** to **lose** a valence. The higher, the easier it is to lose an e. Na=high, Cl=low * **Energy** necessary to remove a specific valence * **Electronegativity** measures the ability of an atom in a xtal structure to **attract** electrons to its outer shell

Answer 8

* **Ionic** donation of e- (NaCl, Fe3O4, Fe2O3) * ^ moderate to high melting point * Soluble in water/acid * low to moderate hardness * Brittle, perfect cleavage * High Symm * Transluscent * **Covalent** sharing when orbitals of 2 atoms overlap (diamonds * ^ very strong bonds * High melting point * high hardness * brittle, variable cleavage * poor solubility * low symmetry * translucent to opaque * **Metallic** many atoms share the same electrons, as such e can move freely throughout structure * ^high electrical and thermal conductivity * variable melting points * low-moderate hardness * high symm * sectile, ductile, malleable * opaque * **VanderWaals and Hydrogen Bonds** weak, electrostatic. The OH in a lattice that makes it cleave *

Answer 9

Fr is the largest. * radii only constant if bond type constant * Ionic size varies depending on CN * Some ions become polarized (elongated) in one direction and no longer act as spehres

Answer 10

Ideal close-packing of sphere for given CN can only be achieved for a specific ionic raidus ratio (RR) between cat and an ions RR=Cation Radius/Anion Radius

Answer 11

When RR is on a CN boundary, PT conditions you can create different xtals from same formula. **Xerals that have identical compositions but different arrangements of atoms and bonds** * Can be used as geobarometers or geothermometers bc of their PT dependance * **Reconstructive**: bonds are broken during the transformation. if PT conditions change, new structure will NOT revert back to original. METASTABLE condition. QUENCHABLE: the reaction is stopped, cannot go backwards. Energy needs to be supplied * **Displacive** bonds are BENT * **Order-Dissorder** distribution of cat and an in lattice affects structure. T plays the most important role * **Polytypism**: the stacking pattern of lattice sheets changes

Answer 12

Hexagonal: ABAB. Cubic: ABCABC * Best describes metals, sulfides, halides, some oxides

Answer 13

1. Coordination Principle: Cat-An ion distances are equal to the sum of their effective ionic radii, cation CN determined by ratio of cation:anion * RR<0.15: CN:2, .15-.22: 3, .22-.41: 4, .41-.73: 6, .73-1: 8. 2. Electrostatic Valence (ev) Principle: **Strength** of ionic (electrostatic) bond between ions is = ionic charge/CN * Isodesmic Xtal: all bonds have same strength. High symm, simple chemical compounds (oxides, fluorides, chlorides * Anisodemic Xtal: ev> ionic charge. Anion will be more strongly bound to central coordinating cation that it can be bonded to other structures. Lower symm, complex chemical compounds (sulphates, carbonates, phosphates) * Mesodesmic: ev = 1/2 the charge on anions (silicates) the O in SiO2 can be equally bonded to central Si and other Si ions 3. Sharing of edges/faces by coordinating polyhedra is inherently unstable 4. Cations of high valence and small CN tend to not share anions w other cations. Silicate minerals, do not contain SiO4 polyhedra sharing edges/faces bc then Si cations too close together. 5. Parsimony: number of different components in a xtal tends to be small ## Footnote 1-4 Maximize the ion attractions and minimize the an-an and cat-cat repulsion

Answer 14

Mineral formula cancels out (no charge)

Answer 15

Occurs in isostructural xerals where different elements (cations) sub for each other. Mechanisms 1. Substitution * one ion replaces another in a particlar size. Ions need to be similar sizes (+-0.15) and charges need to be equal * (Na,Al)Al1-2SI2-3O8 2. Omission * in some cases, leaves sites vacant in lattice. 3. Interstital * Ions substituted into spaces that are usually vacant

Answer 16

1. Availability, and continued avail. of elements. Incompatible elements stay in solution 2. Stability of the growing mineral (ice melts at room T = unstable) 3. Energy of formation must be appropriate (heat and work)

Answer 17

* Open and Closed and Isolated Systems * System: Basalt, Parts: Phases (uniform, homogenous, physically distinct: XERALS) and Components (Smallest building blocks: ELEMENTS)

Answer 18

Number of components in a system is constrained by the number of phases. phases + freedom degrees = component + 2 (PT). f = 2 means that both P and T can vary and we will remain liquid f = 1 means only P or T can vary to be in eq f = 0 fixed point. nothing can change

Answer 19

G = SUM[u(chemical potential of phase) ][n(moles of phase)] The Free Energy can be used to predict direction of rxn deltaG = G (products) - G (reactants) if 0 = equilibrium if < 0 = rxn goes to right if > 0 = rxn goes to the left ## Footnote G(olivine) = n1u(Mg2SiO4) + n2u(Fe2SiO4)

Answer 20

Potential for substance to undergo rxn. Total Pot. = u(products) - u (reactants)

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