15_Chemistry_of_Elements

15_Chemistry_of_Elements - Chemistry of the Elements -...

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Unformatted text preview: Chemistry of the Elements - NonMetals Chapter 22 Chemistry of the Elements 1 Chemistry of the Main Group elements Occurrence of elements Abundance Where in nature State of elements Isola?on and purifica?on Nonmetals Metals (metallurgy) Periodic Trends Size Ioniza?on energy and Electron affinity electronega?vity Trends in Acid/base proper?es Trends in oxida?on states Period II vs. Period III Effects of Bonding: Hydrides For Groups I, II, II, IV and V Metallic Character Trends in bonding Summary of Periodic Trends Chemistry of the Elements 2 Abundance of elements Cosmic abundance Element Atomic No. Rel. Abundance H 1 3.5 x 108 He 2 3.5 x 107 C 6 80,000 N 7 160,000 O 8 210,000 F 9 90 Ne 10 10,000 Na 11 462 Mg 12 8,870 Al 13 882 Si 14 10,000 Cr 24 95 Mn 25 77 Fe 26 18,300 Chemistry of the Elements 3 The periodic table Chemistry of the Elements 4 Abundance of elements Terrestrial abundance Element Atomic No. PPM Rank H 1 8,700 9 He 2 0.003 C 6 800 N 7 300 O 8 495,000 1 F 9 270 Na 11 26,000 6 Mg 12 19,000 8 Al 13 75,000 3 Si 14 257,000 2 K 19 24,000 7 Ca 20 34,000 5 Ti 22 5,800 10 Fe 26 47,000 4 Chemistry of the Elements 5 Standard states of the elements The most stable form of an element at 298 K and 1 atm ("STP") Metals All solids except one (which one?) Nonmetals Atomic gases Noble gases He, Ne, Ar, Kr, Xe, Rn Diatomics halogens and H2, N2, O2 H2, N2, O2 (gas) F2 (gas) Cl2 (gas) Br2 (liquid) I2 (solid) Metalloids All solids Halogens (group 7) Other nonmetals solids C (graphite), S, P, Se Chemistry of the Elements 6 IsolaBon of the Elements From their Natural state Sources of Gas-Phase Nonmetals: 1) HEAVY Noble Gases, O2, N2 - found in atm - obtained via fracBonal disBllaBon 2) Helium volcanoes and geological sites from -decay of radioacBve minerals 3) Halogens a) F2 and Cl2 electrolysis of molten salts b) Br2 and I2 displacement reac?ons (using Cl2) 4) Hydrogen a) Steam Reforming CH4(g) + H2O(g) CO(g) + 3 H2(g) CO(g) + H2O(g) CO2(g) + H2(g) b) Electrolysis of H2O c) ReacBon with acBve metals Chemistry of the Elements 7 IsolaBon of the Elements From their Natural state Sources of Other Nonmetals: 1) Carbon Coal Carbonate ores (CaCO3, MgCO3) 2) Sulfur S8 (yellow solid) mined in Texas 3) P phosphate rock e.g. Ca3(PO4)2 4) Se, Te found in sulfide deposits 5) Boron is rare, found in one mineral: Borax, Na2B4O7(OH2)10 6) Metalloids: found as oxides, sulfides, silicates, aluminosilcates HARD TO EXTRACT Chemistry of the Elements 8 Trends in Bonding Nonmetals: covalent bonding; Oxides and hydroxides = acidic Metals: metallic bonding Metal/nonmetals: ionic; Metal oxides and hydroxides = basic 9 Chemistry of the Elements Effect of Bonding: Periodic II vs. Period III 2s 3s Li Be Na Mg 2p 3p B C N O F Al Si P S Cl Valence: # of covalent bonds an atom prefers 2nd period Only s and p orbitals are possible (n = 2) What is the maximum # of bonds possible? (single and/or double bonds) CH4, NF4+, BH4 3rd (and higher) period Can use d orbitals to make bonds PF5 P is sp3d SF6 S is sp3d2 Chemistry of the Elements 10 Effect of Bonding: Periodic II vs. Period III Double bonds common in Period II but NOT in Period III (usually only single bonds) WHY? Good sidewise overlap of p-orbitals: double and triple bond possible. Poor sidewise overlap: -no mulBple bond Chemistry of the Elements 11 Effect of Bonding: Periodic II vs. Period III O2 is molecular (O=O, has a double bond) But S forms rings with single bonds (e.g., S8) N2 has a triple bond (:NN:, very stable) But phosphorus is found in several forms (white, red, black), all of which have only single bonds. Chemistry of the Elements 12 Effect of Bonding: Periodic II vs. Period III How does valence influence structure? CO2 is molecular (2 double bonds) SiO2 is a 3-dimensional solid network (quartz, sand, glass...) Chemistry of the Elements 13 Hydrogen: It was discovered by Henry Cavendish (17311810). There are three isotopes: ProBum (1H): 99.98% of all hydrogen. Deuterium (2H): 0.016% of all hydrogen TriBum (3H): Radioac?ve Hydrides: binary hydrogen compounds Ionic Metallic Molecular Chemistry of the Elements 14 Form when __________________ react with H2 2 Li + H2 2 LiH Ca + H2 CaH2 Ionic hydrides Form when ________________ react with H2 Molecular hydrides Ionic hydrides can be used as a source of H2 Are basic CaH2 + 2 H2O Ca(OH)2 + 2 H2 Acids: HCl, HBr Recall periodic trends concerning acid strength: PH3 H2S HCl H2O H2S H2Se H2Te Bases: NH3 No acid-base properBes: CH4 Chemistry of the Elements 15 Metallic hydrides Form when __________________ react with H2 Retain ___________________________ Amount of hydrogen in metal hydrides can vary (non-stoichiometric) Hydrogen is typically absorbed by the metal, fijng between the metal atoms in the crystal (inters??al sites) Example: palladium hydride, PdHx (adapted from MRS Bulle?n (cover) Vol. 27 No. 9, Sept., 2002.). Chemistry of the Elements 16 All solids at STP Not found in nature as pure metals, always combined with other elements (e.g. salts in the ocean, minerals) Reac?ve with H2O, O2, and H2 (alkaline earth metals more stable than alkali metals higher ioniza?on energies) AcBve metals (Groups 1 and 2) Group I Group II Family Electronic Config OxidaBon State MelBng Point Bonding Oxides and Hydroxides ElectroposiBve Chemistry of the Elements Alkali Metals ns1 +1 Low Ionic Basic Most Alkaline Earths ns2 +2 Higher Ionic (except Be) Basic (except Be) Yes Harder/Stronger 17 Very ReacBve React with Air, Water TRENDS IN GROUP III OxidaBon states +1 becomes more stable than +3 (Inert pair effect) Basicity of oxides and hydroxides Oxides and hydroxides become more basic B(OH)3 weak acid Al(OH)3 and Ga(OH)3 amphoteric In(OH)3 basic Bonding Covalent (top) ionic (bomom) B is most electronega?ve, forms only covalent bonds Al, Ga, In both covalent and ionic bonds Moving down the group: Chemistry of the Elements 18 TRENDS IN GROUP IV OxidaBon states The +2 oxida?on state becomes more stable than +4 due to the "inert pair" effect. +2 is rare for C, Si, Ge. +2, +4 is common for Sn. +4 is unstable for Pb strong oxidizing agent prefers to be +2. Basicity of oxides and hydroxides Basicity of oxides and hydroxides increases CO2, SiO2, GeO2 are weakly acidic. SnO, SnO2, PbO are amphoteric. Hydrides become less stable THOUSANDS of stable hydrocarbons (compounds of C and H) SiH4 is stable but spontaneously flammable. Ge, Sn, Pb hydrides are very unstable. Chemistry of the Elements 19 Moving down the group Trends in Group V OxidaBon states +3 becomes more stable than +5 (Inert pair effect) Basicity of oxides and hydroxides Oxides and hydroxides become more basic Hydrides become less stable ElectronegaBvity decreases Switch from nonmetallic to metallic Moving down the group: Note the similariBes in trends and properBes for Group 3, 4, and 5 elements the concept of periodicity works and helps us predict and raBonalize the behavior of the elements! Chemistry of the Elements 20 Group 6A Elements Elements in this group have oxida?on states of -2 as well as several posi?ve oxida?on states. They can have expanded octets. Chemistry of the Elements 21 Halogens The halogens have outer electron configura?ons of ns2np5. They have large electron affini?es and ioniza?on energies. They tend to accept one electron to form anions. All have a -1 oxida?on state. All but fluorine also have posi?ve oxida?on states up to +7 when bonded to more electronega?ve atoms. They tend to be good oxidizers, due to their electronega?vity. Chemistry of the Elements 22 Noble Gases Noble gases are extremely stable and unreac?ve. Liquid He (boiling point 4.2 K) is used as a coolant. Ne is used in electric signs. Ar is used in light bulbs and as an insula?ng gas between panes in thermal windows. Of all noble gases, Xe can be forced to form compounds most easily. KrF2 is also known, but decomposes at -10C. Chemistry of the Elements 23 DIAGONAL RELATIONSHIPS In many compounds, Li+ resembles Mg2+ rather than Na+. Examples: Li2CO3 and MgCO3 are virtually insoluble in water, while Na2CO3 is very soluble. Ionic Radii: Li+ 0.60 Na+ 0.95 Be compounds are covalent and the hydroxide is amphoteric Be Mg2+ 0.65 Al Similar to Al (example of a diagonal relationship) Chemistry of the Elements 24 What can we do with this info? What can we actually do with all of this knowledge about the chemistry of the elements? Design new and bejer materials One example: Boron nitride, BN STRUCTURE Boron is one element to the leu of carbon, nitrogen is one to the right Boron nitride (BN) is isoelectronic to carbon (B0.5N0.5 has the same number of electrons as C) BN has similar structures as carbon (graphite and diamond forms) PROPERTIES Diamond is hard (10 on the 1-10 Moh's scale of hardness) BN is 9.8 Diamond is carbon and is not thermally stable in air, while BN is! BN is used instead of diamond as an industrial high-temperature abrasive, in cujng tools, and in drill bits Chemistry of the Elements 25 ...
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