BASICS Start reading White (CH 1) QoD Schedule OUTLINE Periodic table & electronic configurations. Periodic properties: ionic radius, electron negativity, 1st ionization potential Covalent & ionic bonding Hybridization and molecular orbitals Reactions (part 1) 1
WHY DOES IT LOOK LIKE THIS? Note: synthetic = not fake, they are just not stable =..? Chemical behavior controlled by electrons Elements in same columns (periodic behavior) behave similarly due to similar electron configurations. Outer most electrons most important in chemistry since more readily lost and/or shared (= interaction) In contrast, inner electrons are tightly bound to the nucleus by electrostatic forces. 2
Electrons and orbitals 3 p s s Orbital describes where electron could be. 2 electrons fill an orbital 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 = 1s 2 2s 2 2p 6 and Ar = [Ne] 3s 2 3p 6. 3
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- ) Why does it matter? Atomic size matters Only certain sizes fit in any given compound/molecule 1. Atomic radius: decrease increase 4
Common ionic radii Red: active redox chemistry in nature = important for environmental behavior Cations (+), Anions (-) are smaller, bigger than the neutral atom WHY? b/c fewer e- feel the "pull" of the positively charged nucleus Ions behave the same as atoms across the periodic table (row vs column) 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
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]2s 2 3s 2 3p 5 acquires 1 electron to become Cl - = [Ar] configuration. the element K = [[[Ar]4s 1 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
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 Filling shells Lewis dot configuration Configuration graphically shows (dots) how elements can fill their outer shell (p & s blocks) through sharing/bonding. How does this explain H2O below? 7
Bond Character All about e- sharing, but not all bonds share e- equally. 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 H 2 O and air. Bond orbitals Orbitals combine and "hybridize" and 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
Combo example: sp 3 hybridization (C-4atoms) Simplest: element with s + p valence: Tetrahedral coordination hybridize Remind you of anything? If there s too many or too few electrons for this: Nitrogen http://chemwiki.ucdavis.edu/organic_chemistry/organic_chemistry_with_a_biologic al_emphasis/chapter 1%3A_Chapter_1%3A_Introduction_to_organic_structure_an d_bonding_i/section_1.5%3a_valence_bond_theory%3a_sp,_sp2,_and_sp3_hybrid _orbitals Oxygen sp 2 hybridization (planar geometry; C-3atoms) Ex. Carbon double bond: Together make planar set of bonds + perpendicular 2p z planar Planar geometry makes 1 carbon bond, unhybridized p orbital makes p bond, the second (double). This locks molecule: no rotation of left vs right http://chemwiki.ucdavis.edu/organic_chemistry/organic_chemistry_with_a_biologic al_emphasis/chapter 1%3A_Chapter_1%3A_Introduction_to_organic_structure_an d_bonding_i/section_1.5%3a_valence_bond_theory%3a_sp,_sp2,_and_sp3_hybrid _orbitals 9
sp 2 hybridization in the carbonate anion = CO 3 2- Electron DELOCALIZATION O C Vertical orbitals make p system O O http://pages.swcp.com/~jmwmcw/parsing%20spdf%20orbital%20hybridization.html Other bonding interactions hydrogen bonding -Average electron density around O in H 2 O is 10x greater than around H -Exposes the naked protons of H -> molecule partial positive charge -Leads to hydrogen bonding d+ d- d+ d- d+ d+ http://chemwiki.ucdavis.edu/organic_chemistry/organic_chemistry_with_a_biologic al_emphasis/chapter 1%3A_Chapter_1%3A_Introduction_to_organic_structure_an d_bonding_i/section_1.5%3a_valence_bond_theory%3a_sp,_sp2,_and_sp3_hybrid _orbitals 10
Hydrogen bonding Chemical reactions (shuffling bonds) 6 geochemically pertinent chemical reaction types below: Reminder: liquid, vapor, solid and aquous (dissolved) 1. Phase change H 2 O(s) H 2 O(l) H 2 O(g) drives the hydrologic cycle. CaCO 3 (s) (aragonite) CaCO 3 (s) (calcite) formation/preservation of carbonate sediments 11
Chemical reactions 2. Bond Reorganization The Redfield equation of Photosynthesis/Respiration : 106CO 2 +16NO 3- + HPO 4 2- + 122H 2 O +18H + C 106 H 263 O 110 N 16 P + 138O 2 or (CH 2 O) 106 (NH 3 ) 16 (H 3 PO 4 ) + 138O 2 the "Urey" rxn: understanding rock weathering and global controls on atmospheric CO 2 : CaSiO 3 (s) + CO 2 (g) CaCO 3 (s) + SiO 2 (s) Chemical reactions 3. Dissolution/precipitation & Dissolution/gas release CaSO 4 (s) Ca 2+ (aq) + SO 4 2- (aq) NaCl(s) Na + (aq) + Cl - (aq) CO 2 (g) CO 2 (aq) 12
Chemical reactions 4. Oxidation/Reduction - "Redox": electron transfer MnO 2 (s) + 4H + + 2Fe 2+ (aq) Mn 2+ (aq) + 2H 2 O + 2Fe 3+ (aq) Important reaction all over the hydrosphere/geosphere Photosynthesis/Respiration is in this category too How about the picture to the right? 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 Fe 2+ (aq) + 6H 2 O Fe(H 2 O) 6 2+ (aq) hydration of Fe 2+ in water aqueous metal complex with dissolved organic carbon EDTA A common multidentate ligand (EDTA: ethylenediaminetetraacetic acid) 13
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: Fe 2+ + 6H 2 O Fe(H 2 O) 6 2+ H2O stabilizing Fe 2+ 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 :NH 3 (ammonia). All of the following complexes are possible: [FeCl 6 ] -3 [FeCl 3 (NH 3 ) 3 ] 0 [FeCl 2 (NH 3 ) 4 ] + [Fe(NH 3 ) 6 ] +3 Relative proportions will vary with ph since NH 3 + H + NH 4 + (ammonium is not a good ligand) At low ph [FeCl 6 ] -3 would be favored 14
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 15