Elemental abundancesSlide 2OK, which elements shall we stick together? How are they different from each other?Slide 4Earth = anion balls with cations in the spaces…PackingClosest PackingPacking, Coordination, and C.N.Slide 9BondingIonic vs. CovalentMetallic BondsBond CharacterOther types of bondingIonic bondingElemental 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 oxidesPacking•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 arrangementClosest 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 atomsO2NaClIonic 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 symmetryMetallic 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 waterBond CharacterOther 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 ionIonic 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
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