Chapter 22 Chemistry of the Nonmetals

Nonmetals Except for hydrogen, the nonmetals are found in the upper right-hand corner of the periodic chart.

Periodic Trends Within a group, smaller atoms are more likely to form -bonds because they can get closer to other atoms.

Periodic Trends As a result, CO2 contains two -bonds, and SiO2 is a network solid with only -bonds.

Hydrogen Discovered by Henry Cavendish (1731-1810) Three isotopes Protium (1H)  99.98% of all hydrogen Deuterium (2H)  0.016% Tritium (3H)  Radioactive

Properties of Hydrogen Unique Does not belong to any group Very low melting (-259C) and boiling (-253C) points Very large bond enthalpies Reacts slowly Reactions are generally quite exothermic

Hydrogen Production Commercially produced from reaction of methane (CH4) with steam at 1100C or carbon and steam above 1000C CH4 (g) + H2O (g)  CO (g) + 3 H2 (g) CO (g) + H2O (g)  CO2 (g) + H2 (g) C (s) + H2O (g)  H2 (g) + CO (g) Production from electrolysis of water not energy-efficient

Uses of Hydrogen Most hydrogen used to produce ammonia (NH3) in the Haber process Also used to produce methanol (CH3OH) CO (g) + 2 H2 (g)  CH3OH (g)

Uses of Hydrogen 2 H2 (g) + O2 (g)  2 H2O (g) H = -483.6 kJ Using hydrogen as a fuel would have many advantages: Highly exothermic reaction Water is only product Problem: How will we make the H2?

Hydrides Three types Ionic Metallic Molecular

Ionic Hydrides Formed between hydrogen and alkali metals or heavy alkaline earth metals (Ca, Sr, Ba) Very strong bases and reducing agents React readily with water, so must be stored free from moisture

Metallic Hydrides Formed between hydrogen and transition metals, often in unusual ratios e.g., TiH1.8 Retain electrical conductivity and other metallic properties

Molecular Hydrides Formed between hydrogen and nonmetals or metalloids Usually gases or liquids at room temperature and normal atmospheric pressure

Noble Gases Extremely stable and unreactive Liquid He (boiling point 4.2 K) used as a coolant Ne used in electric signs Ar used in light bulbs and as insulating gas between panes in thermal windows.

Xenon Compounds Of all noble gases, Xe can be forced to form compounds most easily KrF2 also known, but decomposes at -10C

Halogens Have outer electron configurations of ns2np5 Large electron affinities and ionization energies Tend to accept one electron to form anion

Halogens All have -1 oxidation state All but fluorine also have positive oxidation states up to +7 when bonded to more electronegative atoms

Properties of Halogens Tend to be good oxidizers, due to their electronegativity Can oxidize anions of halides below them on periodic chart

Properties of Halogens Fluorine has unusually high reduction potential It can easily oxidize water: F2 (aq) + H2O (l)  2 HF (aq) + 1/2 O2 (g) E = 1.80 V

Uses of Halogens Fluorine reacts to form fluorocarbon compounds used as lubricants, refrigerants and plastics. Teflon is a polymer of fluorocarbons.

Uses of Halogens Chlorine is the most-used halogen. HCl Plastics Bleaches Water purification

Uses of Halogens Bromine is the anion for silver in photographic film. KI is added to table salt as a dietary supplement.

Hydrogen Halides Aqueous solutions of HCl, HBr, and HI are, of course, strong acids. HF and HCl can be produced by reacting salts with H2SO4. Br- and I- oxidize too easily, so one must use a weaker oxidizing acid, like H3PO4.

HF Hydrofluoric acid reacts with silicates, components of most types of glass. This reaction causes glass to etch. Therefore, HF is usually stored in plastic containers.

Oxyacids and Oxyanions Oxyacid strength increases with increasing oxidation number of central halogen Oxyacids are strong oxidizers. Oxyanions generally more stable than corresponding acids

Perchlorates While generally quite stable, perchlorates become exceedingly strong oxidizers when heated, and are used as rocket fuel.

Oxygen Joseph Priestley discovered oxygen in 1774. Lavoisier give it its name, which means “acid former.” Most commercial oxygen is obtained from air.

Oxygen Exists as one of two allotropes, O2 and O3 (ozone) Forms very strong bonds Reactions of oxygen-containing compounds have high activation energies Reactions can be very exothermic, even to point of being explosive

Uses of Oxygen Oxidizing agent Bleach pulp and paper Medical uses Welding (with acetylene)

Ozone Bluish gas with sharp odor Extremely irritating to respiratory system Stronger oxidizer than O2 Used to purify water Used in organic synthesis Absorbs UV light in upper atmosphere

Oxides Oxygen is second-most electronegative element Always has negative oxidation state except when bonded to F Acidic oxides like SO2 and SO3 form acids when exposed to water. Basic oxides like BaO form hydroxide ion when they react with water.

Peroxides Oxygen has oxidation state of -1 O-O bond very weak Decomposition of peroxides can be dangerously exothermic

Superoxides Oxygen has oxidation state of -1/2 The most active metals (K, Rb, Cs) form superoxides through reaction with O2 React with H2O to form O2 Source of O2 in self-contained breathing devices

Other Group 6A Elements Have oxidation states of -2 as well as several positive oxidation states Can have expanded octets

Selenium and Tellurium Anions in minerals with Cu, Pb, Ag, and Au Found as helical chains of atoms Selenium not electrically conductive in dark, but quite so in light Used in light meters, photosensors, and photocopiers

Sulfur Solid, yellow compound found in 8-membered ring As heated to melting, ring breaks and sulfur becomes viscous, reddish-brown liquid

Sulfur Most sulfur used for H2SO4 and for vulcanization of rubber

Pyrites Contain disulfide ion, S22-, the sulfur analog of peroxide Found in minerals like iron pyrite (fool’s gold)

Sulfides To say that many sulfides have rather unpleasant odors is a gross understatement. H2S is emitted by rotten eggs. Many minerals like galena (PbS) and cinnabar (HgS) are sulfides.

Sulfur Oxides, Oxyacids, and Oxyanions SO2 is a poison, particularly to lower organisms. Used to sterilize dried fruit and wine Dissolves in H2O to form H2SO3 Sulfites and bisulfites added to foods and wines to kill bacteria

Sulfur Oxides, Oxyacids, and Oxyanions Sulfuric acid Strong acid Good dehydrating agent Decent oxidizer

Sulfur Oxides, Oxyacids, and Oxyanions Thiosulfate ion resembles sulfate ion (a S replaces one of the O’s in sulfate) Sodium thiosulfate pentahydrate (Na2S2O35 H2O) used in photography to remove unexposed AgBr from film as soluble complex of thiosulfate Sulfate Thiosulfate

Nitrogen Discovered in 1772 by Daniel Rutherford Makes up 78% of Earth’s atmosphere Can exist in oxidation states from -3 to +5

Nitrogen Many nitrogen-containing compounds strong oxidizers N2 made into NH3 in Haber process NH3 is precursor to many other compounds

Ammonia Hydrazines made from ammonia One intermediate is chloramine (NH2Cl), poisonous compound produced when household ammonia and hypochlorite ion in bleach are mixed Hydrazines are strong oxidizers used in rocket fuels

Oxides and Oxyacids Nitrous oxide (N2O; laughing gas) was the first general anesthetic. It is also used in aerosol products like whipped cream.

Oxides and Oxyacids Nitric oxide (NO) is a slightly toxic, colorless gas. Recently shown to be neurotransmitter in humans involved in vasodilation Reacts with O2 in air to produce nitrogen dioxide, NO2

Oxides and Oxyacids Nitric acid Nitrous acid Strong acid and oxidizer Used in fertilizer and explosive production (TNT, nitrocellulose, nitroglycerine) Nitrous acid Less stable, yet weaker acid than HNO3

Other Group 5A Elements This group contains nonmetals (N and P), a metal (Bi), and metalloids (As and Sb).

Phosphorus Two allotropes White phosphorus (P4) Red phosphorus Highly strained Bursts into flames if exposed to O2 in air Red phosphorus Very stable

Oxyphosphorus Compounds Phosphorus(III) oxide (P4O6) and phosphorus(V) oxide (P4O10) are anhydride forms of phosphorous (H3PO3) and phosphoric (H3PO4) acids

Oxyphosphorus Compounds These acids condense to form polymeric forms. Phosphoric acid and phosphates are found in detergents, fertilizers, and important biomolecules like DNA, RNA, and ATP.

Carbon Exists as four allotropes: Graphite Diamond Fullerenes Carbon nanotubules Graphite converted to diamond (at 100,000 atm and 3000C) for industrial uses

Carbon Oxides Carbon monoxide (CO) Carbon dioxide (CO2) Odorless, colorless gas Binds preferentially to iron in hemoglobin, inhibiting O2 transport Used as fuel, reducing agent in metallurgy, and precursor to organic compounds Carbon dioxide (CO2) Used to carbonate beverages, decaffeinate products (in its supercritical form) and as a refrigerant (as Dry IceTM)

Carbonic Acid and Carbonates Dissolved CO2 in water is in equilibrium with carbonic acid, H2CO3 Carbonates found as minerals like calcite, CaCO3, the primary constituent of limestone

Silicon Second most abundant element in Earth’s crust Semiconductor used in making transistors and solar cells Purified by zone-refining

Silicates Have a central silicon surrounded by 4 oxygens In disilicate, two tetrahedral structures share one oxygen Silicate Disilicate

Silicates These units can further connect into sheets or strands. Talc and asbestos are two examples of molecules containing these structures.

Boron The only nonmetallic Group 3A element Compounds of boron and hydrogen are called boranes. Because boron does not have a filled octet, structures such as diborane, in which two borons share one hydrogen are possible.

Boron Borane anions, such as borohydride, BH4-, are good reducing agents and sources of hydride ion.