Term
| 2 principal reasons that the types of bonds that occur in minerals are important |
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Definition
1: the physical and chemical properties of all materials depend on the character of the bonds that hold them together
2: weathering rxns and the stability of soil minerals are functions of the nature of the crystal chemical bonds |
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Term
| the physical and chemical properties of all materials depend on... |
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Definition
| the character of the bonds that hold them together |
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Term
| weathering rxns and the stability of soil minerals are functions of... |
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Definition
| the nature of the crystal chemical bonds |
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Term
| the importance of the weakest bond type in a mineral |
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Definition
| to a large extent, this dictates the mineral's physical and chemical properties |
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Term
| the strongest bonds in soil minerals |
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Definition
| the ones that are predominantly covalent in character |
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Term
| the relative stability of a mineral in a weathering environment is determined by... |
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Definition
| the ionic bonds that are inherent to the mineral |
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Term
| the ion that dominates in soil minerals |
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Definition
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Term
| some factors that must be considered when predicting the arrangement of atoms in a mineral |
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Definition
-geometric packing constraints
-electrostatic interactions between atoms |
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Term
| the rules that describe the likely geometric arrangement of atoms in an ionic structure |
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Definition
| Pauling's rules of crystal configuration |
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Term
| Pauling's 1st rule of crystal configuration |
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Definition
| a coordinated polyhedron of anions is formed about each cation, the cation-anion distance being determined by the radius sum and the coordination number of the cation by the radius ratio |
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Term
| this determines the cation-anion distance |
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Definition
| the sum of the radius of the cation and the radius of the anion (this is the radius sum) |
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Term
| this determines the coordination number of the cation |
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Definition
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Term
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Definition
| the number of anions that can pack around a single anion |
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Term
| the coordination number of a cation is a function of... |
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Definition
| cation size and anion size (radius) |
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Term
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Definition
| (cation radius)/(anion radius) |
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Term
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Definition
| the radius ratio at which the coordinating anions just touch; if the cation was any smaller, the anions would overlap and repel each other, making the structure unstable and making a lower coordination number necessary |
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Term
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Definition
| if the central cation has room to move inside a given polyhedron, the configuration is unstable |
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Term
| polyhedron type with coordination number of 2 |
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Definition
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Term
| polyhedron type with coordination number of 3 |
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Definition
| planar triangular or trigonal pyramidal |
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Term
| polyhedron type with coordination number of 4 |
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Definition
| tetrahedral or planar square |
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Term
| polyhedron type with coordination number of 6 |
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Definition
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Term
| polyhedron type with coordination number of 8 |
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Definition
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Term
| polyhedron type with coordination number of 12 |
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Definition
| dodecahedral or cubooctahedral |
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Term
| size of central metal atom vs. coordination number |
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Definition
| as the size of the central metal atom increases, the coordination number increases |
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Term
| Pauling's 2nd rule of crystal configuration (aka the electrostatic valence principle) |
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Definition
| in a stable structure, the valence of each anion, with changed sign, is equal or nearly equal to the sum of the strengths of the electrostatic bonds to it from adjacent cations |
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Term
| how to calculate bond strength |
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Definition
| bond strength = (cation valence) / (coordination number) |
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Term
| coordination number for linear polyhedron |
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Definition
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Term
| coordination number for planar triangular or trigonal pyramidal polyhedron |
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Definition
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Term
| coordination number for tetrahedral or planar square polyhedron |
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Definition
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Term
| coordination number for octahedral polyhedron |
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Definition
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Term
| coordination number for cubic polyhedron |
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Definition
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Term
| coordination number for dodecahedral or cubooctahedral polyhedron |
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Definition
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Term
| Pauling's 3rd rule of crystal configuration |
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Definition
| the presence of shared edges and especially shared faces in a coordinated structure decreases its stability; the effect is larger for cations with large valence and small coordination number (lignancy) |
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Term
| distance between cations vs. stability of the mineral structure |
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Definition
| the greater the distance between the cations, the more stable the structure becomes; direct relationship |
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Term
| out ofg anions that are shared by polyhedrons at the face, corner, and edge, which is the most stable and which is the least stable? |
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Definition
most stable: corner
least stable: face |
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Term
| Pauling's 4th rule of crystal configuration |
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Definition
| in a crystal containing different cations, those with large valence and small coordination number tend not to share polyhedron elements with each other |
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Term
| how the electrostatic interaction of high valence cations is minimized in stable structures |
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Definition
| thru the shielding provided by the coordinating anions |
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Term
| size of cation vs. stability of structure |
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Definition
| the larger the cation, the more stable the structure, pending everything else is equal; direct relationship |
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Term
| charge density vs. stability of structure |
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Definition
| the higher the charge density, the less stable the structure, pendine everything else is equal; inverse relationship |
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Term
| Pauling's 5th rule of crystal configuration (the principal of parsimony) |
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Definition
| the number of essentially different kinds of atoms or coordinated polyhedron in a crystal tends to be small; this is a natural consequence of the other 4 rules |
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Term
| this dictates the presence of a cation in a given polyhedral configuration |
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Definition
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Term
| the principal of parsimony |
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Definition
| states that a stable structure will contain only a small number of essentially different kinds of atoms |
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Term
| 2 readily apparent reasons that support the validity of the principal of parsimony |
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Definition
1: although several different cations can reside in a particular coordination, generally only 1 particular cation fits best in the structure (is best suited for the location); other cations, which are not as well suited for that location, cause stress and instability
2: a +4 or +6 cation residing in a location normally occupied by a +2 cation will result in electrostatic imbalances, destabilizing the structure |
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