Elemental abundances O 62 5 atomic Si 21 2 Al 6 5 Fe 1 9 Ca 1 9 Na 2 6 K 1 42 Mg 1 84 Nuclear reactions determine element abundance Is the earth homogeneous though Is the solar system Is the universe OK which elements shall we stick together How are they different from each other Earth anion balls with cations in the spaces View of the earth as a system of anions packed together By size and abundance Si and O are the most important If we consider anions as balls then their arrangement is one of efficient packing with smaller cations in the interstices Closest packed structures are ones in which this idea describes atomic arrangement OK for metals sulfides halides some oxides Packing Spheres and how they are put together HCP and CCP models are geometrical constructs of how tightly we can assemble spheres in a space Insertion of smaller cations into closest packed arrays yield different C N s based on how big a void is created depending on arrangement Closest Packing Coordination number C N of anions bonded to a cation larger cation higher C N Anions are much larger than most cations anion arrangements in 3 dimensions packing Hexagonal Closest Packed HCP spheres lie atop each other vertical sequence ABABAB Cubic closest packed CCP spheres fill in gaps of layer below vertical sequence ABCABC Exceptions to closest packing Body centered cubic BCC polyhedra and others Packing Coordination and C N Principle difference between hexagonal and cubic closest packing is repeat sequence ABABAB for hexagonal ABCABCABC for cubic To classify there are different types of hexagonal and cubic packed possibilities A close packed plane can yield either 3D structure depending on how it is layered and a single type of structure does not yield a single type of site more than one site with different C N is possible Which is this Bonding Atoms come together in one of 3 principle types of bond Ionic and ions charged atoms joined by an electrostatic interaction Covalent Sharing of electrons equally between ions Metallic sharing of electrons between many atoms O2 NaCl Ionic vs Covalent Elements on the right and top of the periodic table draw electrons strongly Bonds between atoms from opposite ends more covalent diatomics are 100 covalent Bond strength Covalent Ionic metallic Affects hardness melting T solubility Bond type affects geometry of how ions are arranged More ionic vs covalent higher symmetry Metallic Bonds Electron sharing can go in any direction results in more malleable material Also affects electronic properties metallic materials conduct electricity better Affects redox reactions where there is a transfer of electrons as a part of dissolution In M O electrons are nonbonding or delocalized This also makes materials less polar and thus less soluble is water Bond Character Other types of bonding Van der Waals Interaction between molecular units which assemble a mineral from weak electrostatic interactions Hydrogen H bonds molecular subunits together Dative special type of covalent bond all bonding electrons donated by one ion Ionic bonding Most common minerals on earth are composed of ionic bonds Covalently bonded anionic subunits are often ionically bonded to cations to form these minerals SiO44 CO32 PO43 SO42 Mineral properties are more often compared by the anionic component thus most classification schemes focus on this
View Full Document
Unlocking...