Oxygen Chapter 18
Oxygen Oxygen compounds are known of all elements Except: He,Ne and possibly Ar Oxygen Chemisrty involves Obtaining Ne configuration by one of the following means
Oxygen • 1.) Electron gain to form the Oxide O2- • 2.) Formation of 2 single bonds usually in bent systems such as water or ethers. • 3.) Formation of a double bond (org. Compounds) • 4.) Formation of a single bond, as well as electron gain such as OH- • 5.) Formation of three covalent bonds such as in H3O+ • 6.) Formation in rare cases of 4 covalent bonds
Oxygen Oxygen has the possibility of a broad range of bond types from ionic to covalent, which is seen in the binary oxides. Highly ionic ones alakli and alkaline earh metal oxides Completely covalent ones CO2 Intermediates B,Al, Si
Ionic Oxides Formation of Oxide ion from Oxygen requires 1000 kJ/mol. The stability of ionic metal oxides comes from the high lattice energies with the small and highly charged oxide ion.
Ionic oxides Wen the lattice energy is not sufficient to offset the eneries for ionisation, oxides with more covalent character are formed. Oxides with some covalent character. BeO SiO2 B2O3
Covalent or molecular Oxides Covalent oxides are compounds such as: CO2 SO2 SO3 NO2 Dominated by Covalent bonding An important aspect of bonding of molecular oxides is the use of p-orbitals in π bonding wit other atoms.
Covalent Oxides • pπ- pπ bonding is found in ketones (organic compound) • pπ- dπ bonding is found in • phosphine oxides (R3P=O) • or • linear M=O=M systems • Terminal Oxygen atoms with 3 lone pairs • (OH)- • These Oxygen atoms are sp3 hybridized
Covalent Oxides Covalent compounds with oxides with 2 lone pairs of electrons are typically angular molecules. Water (104.5˚) Alcohols Ethers Oxygen atoms are sp3 hybridized.
Covalent Oxides Atoms with d orbitals pπ –dπ is often present in the bond to oxygen. Si-O-Si in quartz 142˚ H3Si-O-SiH3 is greater than 150˚ Linear molecules are found in systems with transition metals.
Covalent Oxides The Oxonium Ion :OH3+ sp3 hybridized Oxonium Ion formation is analogous to the formation of ammonium ions. Oxygen is less basic than nitrogen, oxonium ions are less stable. OH42+ is unlikely repulsion towards proton Oxonium ions undergo rapid inversion
Acid - Base properties of Oxides Basic Oxides Dissolve in dilute acids:
Acid - Base properties of Oxides Acidic Oxides Covalent non metal oxides are acidic Unsoluble oxides will dissolve in bases
Acid - Base properties of Oxides • Amphoteric Oxides • Other Oxides • Redox than acid-base
Occurrence, Properties Oxygen has 3 isotopes 2allotropes (O2) and (O3) O2 is paramagnetic has a high dissociation energy Ozone Is diamagnetic Electrical discharge produces Ozone
Chemical Properties Ozone is an oxidizing agent. Oxidizing Potential
Hydrogen Peroxide Colorless Liquid Resembles water Igher hydrogen bound 40% denser than water High Dielectric constant Strong oxidizing agent Heavy metal traces act as catalysts in dissociation reactions
Hydrogen Peroxide In dilute aqueous solutions: More acidic than water Production of peroxide:
S,Se,Te,Po S,Se,Te,Po have lower electronegativities than oxygen Compounds less ionic Relative stabilities of bonds is different H-bonding is lower S---H--S bonds exist but are very weak Like all others S has dπ- pπ bonds SO42- has multiple dπ- pπ bonds.
S,Se,Te,Po The valence for S,Se,Te,Po is not confined to 2, and d orbitals can be used to form more than 4 bonds to other elements. SF6 S has a strong tendency to catenation It forms polysulfide ions, polythionate ions
S,Se,Te,Po Changes in properties from S to Po Size of atoms increase Electronegativity decreases 1. The decreasing stability of the hydrides . 2. The increasing tendency to form complex ions such as SeBr62-. 3. The appearance of metallic properties for Te and Po atoms. Thus the oxides M02are ionic and basic, reacting with HCI to give the chlorides.
Occurrence Sulfur occurs widely in nature as the element, as H 2S and S02, in metal sulfide ores, and as sulfates [e.g., gypsum and anhydrite (CaS04), magnesium sulfate, and so on].
Occurrence Selenium and tellurium are less abundant but frequently occur as selenide and telluride minerals in sulfide ores, particularly those of Ag and Au. Polonium occurs in U and Th minerals as a product of radioactive decay series. The most accessible isotope, 21OpO (a, 138.4 days), can be made in gram quantities by irradiation of Bi in nuclear reactors.
Occurrence On melting, Ss first gives a yellow, transparent, mobile liquid that becomes dark and increasingly viscous above about 160°C. The maximum viscosity occurs about 200 °C, but on further heating the mobility increases until the boiling point (444.6 0C), where the liquid is dark red.
Occurrence Sulfur vapor contains S8 and at higher temperatures S2 molecules. The latter, like 02 are paramagnetic with two unpaired electrons, and account for the blue color of the hot vapor. The elements S, Se, and Te burn in air on heating to form the dioxides; they also react on heating with halogens, most metals, and nonmetals. They are attacked by hot oxidizing acids like H2S04or HNO3.
Occurrence The S,Se and Te 2+ ions are square
Occurrence All reactions of S8 must involve initial ring opening to give sulfur chains or chain compounds. Many involve nucleophilic reactants, for example,
Hydrides The hydrides are extremely poisonous gases with revolting odors. The toxicity of H 2S far exceeds that of HCN. The thermal stability and bond strengths decrease down the series, whereas the acidity in water increases. Hydrogen sulfide dissolves in water to give a solution about 0.1 M at 1 atm.
SOCl2 It is a colorless fuming liquid (bp 80 degC) that is readily hydrolyzed as in Reaction Since the products are volatile it is used to prepare IronChloride
Dioxides The dioxides are obtained by burning the elements in air. Sulfur dioxide is produced when many sulfides are heated in air. Selenium and tellurium dioxides are also obtained by treating the elements with hot nitric acid to form H2Se03and 2 Te02·HN03 heating these drives off water or nitric acid.
SO2 Sulfur dioxide has lone pairs and can act as a Lewis base. However, it also acts as a Lewis acid giving complexes, for example, with amines, as in (CH3hNS02 and with electron-rich transition metal complexes.
SO2 Sulfur dioxide is quite soluble in water; such solutions, which possess acidic properties, have long been referred to as solutions of sulfurous acid, H2S03
Trioxides Sulfur trioxide is obtained by reaction of S02 with 02 reaction needs a catalyst such as platinum sponge, V205 or N0. Sulfur trioxide reacts vigorously with water to form sulfuric acid. Industrially, S03 is absorbed in concentrated H2S04 to give oleum , which is then diluted.