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8/24/16 BASICS OUTLINE • Periodic table & electronic configurations. • Periodic properties: ionic radius, electron negativity, 1st ionization potential • Covalent & ionic bonding • Hybridization and molecular orbitals • Reactions (part 1) WHITE (CH 1) 1 8/24/16 WHY DOES IT LOOK LIKE THIS? Chemical behavior controlled by electrons Elements in same columns (periodic behavior) behave similarly due to similar electron configura:ons. Outer most electrons most important in chemistry since more readily lost and/or shared (= interac:on) In contrast, inner electrons are :ghtly bound to the nucleus by electrosta:c forces. 2 8/24/16 Electrons and orbitals • Orbital describes where electron could be. • 2 electrons “fill” an orbital “s” 3 “p”s – “s” orbitals spherical – “p” pairs of “lobes” – “d” &”f” more complex • Orbital geometry control how electrons are shared => molecular geometry 5 “d” s Note: the 14 “f”s are not shown Filling of 1s orbital – how many columns? Filling of higher “s” orbitals “d” orbitals! How many columns? “p” orbitals! Count columns? “f” orbitals! Count columns Filled orbital assignment shorthand notation: Ne = 1s2 2s2 2p6 and Ar = [Ne] 3s2 3p6. 3 8/24/16 Electron configuration – packing all those electrons Aufbau Principle Simplified ! Low energy orbital fills 1st. ! s: 2, p: 6, d: 10, f:14, (in sets of 2: 1*2, 3*2, 5*2, 7*2) ! Each set of 2 can host 2 e- with opposite spin Electron configurations w/ full or half-full orbitals are “preferred” because they are more stable. ! full = orbitals with paired spins ! half = only 1 spin direction (e.g. p with 3*1e- ) Review Periodic Properties from Introductory Chemistry 1. Atomic radius: ►Radii of the elements increase down a column decrease across a row (left to right). 2. Ion size (ionic radius) + ion smaller than the neutral atom b/c fewer e- feel the "pull" of the positively charged nucleus - ion is larger than the neutral atom Ions behave the same as atoms across the periodic table (row vs column Importance of the radius: molecules can only “fit” certain sizes 4 8/24/16 ionic radii of common ions in common ionization state Remember: many elements have more than one stable “valance”. Elements lettered in red have active “redox” chemistry in nature = important for environmental behavior. Remember: oxidation = loss of electrons; reduction = gaining electrons. Ionization and Ionization Energy (aka ionization potential): Ionization energy measures how easy or hard it is to remove an electron from an element or ion. Energies of filled electronic orbitals give rise to common oxidation states for individual elements. Electronic structure determines ionic charge and IE. 5 8/24/16 Oxidation states and the periodic table ►noble gasses have filled valence shells. They rarely ionize (except Xe), or interact ►all other elements “want to” fill their valence shells too. Examples ► the element Cl = [Ne]2s2 3s2 3p5 acquires 1 electron to become Cl- = [Ar] configuration. ► the element K = [[[Ar]4s1 loses 1 electron to attain an [Ar] electronic configuration (K+ = [Ar]). Low IP But use caution with a generalization like this, because other factors come to bear High IP Noble gas: filled shell high IP: hard to remove e- Would rather gain e- instead of losing 1: high IP Low IP to lose e- for a filled shell IP = ionization potential 6 8/24/16 Electronegativity Measures desire to gain an electron. Classification by electronegativity as: a. donors (+ ions) Low electronegativity = nearly empty valence shell= gives up electrons easily b. acceptors (- ions) high electronegativity = mostly filled valence shell c. inert (noble gases). Electronegativity ≥ 2.5 is a quasi chemical dividing line GG325 L2, F2013 7 8/24/16 Bond Character All about e- sharing, but not all bonds share e- equally. Two end members: - Pure Covalent Bond = 2 atoms bond with same electronegativity spectrum of options in between - Pure Ionic Bond = largest possible electronegativity difference Bond character affects how ionically-bonded solids ("salts") and covalently-bonded solids (quartz, octane, etc..) behave in H2O and air. Bond orbitals Atomic orbitals combine and "hybridize" to make bonding and non-bonding orbitals that define electron density between atoms. e.g. sharing between 2 s orbitals s and p orbital, 2 p orbitals But some elements have more to share… http://chemwiki.ucdavis.edu/Organic_Chemistry/Organic_Chemistry_With_a_Biological_Emphasis/… …Chapter__1%3A_Chapter_1%3A_Introduction_to_organic_structure_and_bonding_I/… …Section_1.5%3A_Valence_bond_theory%3A_sp,_sp2,_and_sp3_hybrid_orbitals 8 8/24/16 Combo example: sp3 hybridization Simplest: element with s + p valence: Tetrahedral coordination hybridize Remind you of anything? http://chemwiki.ucdavis.edu/Organic_Chemistry/ Organic_Chemistry_With_a_Biological_Emphasis/ Chapter__1%3A_Chapter_1%3A_Introduction_to_organic_structure_and_bonding_I/ Section_1.5%3A_Valence_bond_theory%3A_sp,_sp2,_and_sp3_hybrid_orbitals If there’s too many or too few electrons for this: Nitrogen Oxygen sp2 hybridization (planar geometry) Ex. Carbon double bond: Together make planar set of bonds + perpendicular 2pz planar Planar geometry makes 1 carbon bond, unhybridized p orbital makes π bond, the second (double). This locks molecule: no rotation of left vs right http://chemwiki.ucdavis.edu/Organic_Chemistry/ Organic_Chemistry_With_a_Biological_Emphasis/ Chapter__1%3A_Chapter_1%3A_Introduction_to_organic_structure_and_bonding_I/ Section_1.5%3A_Valence_bond_theory%3A_sp,_sp2,_and_sp3_hybrid_orbitals 9 8/24/16 sp2 hybridization in the carbonate anion = CO32Electron DELOCALIZATION O Ver:cal orbitals make π system C O O http://pages.swcp.com/~jmw-mcw/Parsing%20spdf%20orbital %20hybridization.html Other bonding interactions – hydrogen bonding -Average electron density around O in H2O is 10x greater than around H -Exposes the “naked” protons of H -> molecule partial positive charge -Leads to hydrogen bonding δδ+ δ- δ+ δ+ δ+ http://chemwiki.ucdavis.edu/Organic_Chemistry/ Organic_Chemistry_With_a_Biological_Emphasis/ Chapter__1%3A_Chapter_1%3A_Introduction_to_organic_structure_and_bonding_I/ Section_1.5%3A_Valence_bond_theory%3A_sp,_sp2,_and_sp3_hybrid_orbitals 10 8/24/16 Hydrogen bonding Chemical reactions 6 geochemically pertinent chemical reaction types below: Reminder: liquid, vapor, solid and aquous (dissolved) 1. Phase change H2O(s) ↔ H2O(l) ↔H2O(g) drives the hydrologic cycle. CaCO3 (s) (aragonite) ↔CaCO3 (s) (calcite) formation/preservation of carbonate sediments 11 8/24/16 Chemical reactions 2. Bond Reorganization The Redfield equation of Photosynthesis/Respiration : 106CO2 +16NO3- + HPO42- + 122H2O +18H+ ↑↓ C106H263O110N16P + 138O2 or (CH2O)106(NH3)16(H3PO4) + 138O2 the "Urey" rxn: understanding rock weathering and global controls on atmospheric CO2: CaSiO3(s) + CO2(g) ↔ CaCO3(s) + SiO2(s) Chemical reactions 3. Dissolution/precipitation & Dissolution/gas release CaSO4(s) ↔ Ca2+(aq) + SO42-(aq) NaCl(s) ↔ Na+(aq) + Cl-(aq) CO2 (g) ↔ CO2 (aq) 12 8/24/16 Chemical reactions 4. Oxidation/Reduction - "Redox": electron transfer MnO2(s) + 4H+ + 2Fe2+(aq) ↔ Mn2+(aq) + 2H2O + 2Fe3+(aq) An important reaction all over the hydrosphere/geosphere Photosynthesis/Respiration is in this category too 5. ion substitution We’ll see a number this semester. Na+ (aq) + [clay mineral]-K+ ↔ K+ (aq) + [clay mineral]-Na+ cation exchange between a clay mineral and ions in water Chemical reactions 6. Complexation/Chelation Fe2+(aq) + 6H2O ↔ Fe(H2O)62+ (aq) hydration of Fe2+ in water aqueous metal complex with dissolved organic carbon EDTA A common multidentate ligand (EDTA: ethylenediaminetetraacetic acid) 13 8/24/16 Complexation/chelation Complexes involve ligands and host ions. Ligand: ion/molecule that binds to a central metal atom; host: metal atom Hydration is type of complexation reaction; ligands are water: Fe2+ + 6H2O ↔ Fe(H2O)62+ H2O stabilizing Fe2+ ion with electron pair. The hydrate itself involves 5 other water molecules. More on ligands Unidentate: offer electrons from a single site to a complex; ex: H2O, Cl- (chloride) and :NH3 (ammonia). All of the following complexes are possible: [FeCl6]-3 [FeCl3(NH3)3]0 [FeCl2(NH3)4]+ [Fe(NH3)6]+3 Relative proportions will vary with pH since NH3 + H+ ↔ NH4+ (ammonium is not a good ligand) At low pH [FeCl6]-3 would be favored GG325 L3, F2012 14 8/24/16 More more on ligands Chelation complexation that involves multidentate ligands. A chelate is complex with multidentate ligand. A multidentate ligand more than 1 e- pair to donate to cation. Simplest is: bidentate ligand has 2 active binding sites for a cation. e.g., ethylene diamine, :NH2-CH2-CH2-H2N: and oxalic acid/oxylate anion More more more on ligands Bidendate ligands can bind in two ways: cis: next to trans: across M is a metal or other cation and B is where the donor electron pairs are in the ligand. "small" bidentate ligand such as ethylene diamine (NH2-CH2=CH2-NH2) usually bind cis for geometric reasons. 15