Chapter 22 Chemistry of the Nonmetals
-
Upload
cally-allison -
Category
Documents
-
view
56 -
download
8
description
Transcript of Chapter 22 Chemistry of the Nonmetals
Nonmetals
Chapter 22Chemistry of the
Nonmetals
Chemistry, The Central Science, 10th editionTheodore L. Brown, H. Eugene LeMay, Jr.,
and Bruce E. Bursten
John D. BookstaverSt. Charles Community College
St. Peters, MO 2006, Prentice-Hall, Inc.
Nonmetals
Nonmetals
Except for hydrogen, the nonmetals are found in the upper right-hand corner of the periodic chart.
Nonmetals
Periodic Trends
Within a group, smaller atoms are more likely to form -bonds because they can get closer to other atoms.
Nonmetals
Periodic Trends
As a result, CO2 contains two -bonds, and SiO2 is a network solid with only -bonds.
Nonmetals
Hydrogen
• Discovered by Henry Cavendish (1731-1810)
• Three isotopesProtium (1H) 99.98% of
all hydrogenDeuterium (2H) 0.016%Tritium (3H) Radioactive
Nonmetals
Properties of Hydrogen
• UniqueDoes not belong to any group
• Very low melting (-259C) and boiling (-253C) points
• Very large bond enthalpiesReacts slowlyReactions are generally quite exothermic
Nonmetals
Hydrogen Production• Commercially produced from reaction of methane
(CH4) with steam at 1100C or carbon and steam above 1000C
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
Nonmetals
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)
Nonmetals
Uses of Hydrogen
• Using hydrogen as a fuel would have many advantages:Highly exothermic reactionWater is only product
• Problem: How will we make the H2?
2 H2 (g) + O2 (g) 2 H2O (g) H = -483.6 kJ
Nonmetals
Hydrides
• Three typesIonicMetallicMolecular
Nonmetals
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
Nonmetals
Metallic Hydrides
• Formed between hydrogen and transition metals, often in unusual ratiose.g., TiH1.8
• Retain electrical conductivity and other metallic properties
Nonmetals
Molecular Hydrides
• Formed between hydrogen and nonmetals or metalloids
• Usually gases or liquids at room temperature and normal atmospheric pressure
Nonmetals
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.
Nonmetals
Xenon Compounds
• Of all noble gases, Xe can be forced to form compounds most easily
• KrF2 also known, but decomposes at -10C
Nonmetals
Halogens
• Have outer electron configurations of ns2np5
• Large electron affinities and ionization energies
• Tend to accept one electron to form anion
Nonmetals
Halogens
• All have -1 oxidation state
• All but fluorine also have positive oxidation states up to +7 when bonded to more electronegative atoms
Nonmetals
Properties of Halogens
• Tend to be good oxidizers, due to their electronegativity
• Can oxidize anions of halides below them on periodic chart
Nonmetals
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
Nonmetals
Uses of Halogens
• Fluorine reacts to form fluorocarbon compounds used as lubricants, refrigerants and plastics.
• Teflon is a polymer of fluorocarbons.
Nonmetals
Uses of Halogens
• Chlorine is the most-used halogen.HClPlasticsBleachesWater purification
Nonmetals
Uses of Halogens
• Bromine is the anion for silver in photographic film.
• KI is added to table salt as a dietary supplement.
Nonmetals
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.
Nonmetals
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.
Nonmetals
Oxyacids and Oxyanions
• Oxyacid strength increases with increasing oxidation number of central halogen
• Oxyacids are strong oxidizers.• Oxyanions generally more stable than
corresponding acids
Nonmetals
Perchlorates
While generally quite stable, perchlorates become exceedingly strong oxidizers when heated, and are used as rocket fuel.
Nonmetals
Oxygen
• Joseph Priestley discovered oxygen in 1774.
• Lavoisier give it its name, which means “acid former.”
• Most commercial oxygen is obtained from air.
Nonmetals
Oxygen
• Exists as one of two allotropes, O2 and O3 (ozone)
• Forms very strong bondsReactions of oxygen-containing
compounds have high activation energiesReactions can be very exothermic, even to
point of being explosive
Nonmetals
Uses of Oxygen
• Oxidizing agentBleach pulp and
paperMedical usesWelding (with
acetylene)
Nonmetals
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
Nonmetals
Oxides• Oxygen is second-most
electronegative elementAlways 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.
Nonmetals
Peroxides
• Oxygen has oxidation state of -1
• O-O bond very weakDecomposition of
peroxides can be dangerously exothermic
Nonmetals
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
Nonmetals
Other Group 6A Elements
• Have oxidation states of -2 as well as several positive oxidation states
• Can have expanded octets
Nonmetals
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 lightUsed in light meters,
photosensors, and photocopiers
Nonmetals
Sulfur
• Solid, yellow compound found in 8-membered ring
• As heated to melting, ring breaks and sulfur becomes viscous, reddish-brown liquid
Nonmetals
Sulfur
• Most sulfur used for H2SO4 and for vulcanization of rubber
Nonmetals
Pyrites
• Contain disulfide ion, S2
2-, the sulfur analog of peroxide
• Found in minerals like iron pyrite (fool’s gold)
Nonmetals
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.
Nonmetals
Sulfur Oxides, Oxyacids, and Oxyanions
• SO2 is a poison, particularly to lower organisms.Used to sterilize dried fruit and wineDissolves in H2O to form H2SO3
• Sulfites and bisulfites added to foods and wines to kill bacteria
Nonmetals
Sulfur Oxides, Oxyacids, and Oxyanions
• Sulfuric acidStrong acidGood dehydrating agentDecent oxidizer
Nonmetals
Sulfur Oxides, Oxyacids, and Oxyanions
• Thiosulfate ion resembles sulfate ion (a S replaces one of the O’s in sulfate)
• Sodium thiosulfate pentahydrate (Na2S2O35 H2O) used in photography to remove unexposed AgBr from film as soluble complex of thiosulfate
Sulfate
Thiosulfate
Nonmetals
Nitrogen
• Discovered in 1772 by Daniel Rutherford
• Makes up 78% of Earth’s atmosphere
• Can exist in oxidation states from -3 to +5
Nonmetals
Nitrogen• Many nitrogen-
containing compounds strong oxidizers
• N2 made into NH3 in Haber processNH3 is
precursor to many other compounds
Nonmetals
Ammonia
• Hydrazines made from ammoniaOne 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
Nonmetals
Oxides and Oxyacids
• Nitrous oxide (N2O; laughing gas) was the first general anesthetic.
• It is also used in aerosol products like whipped cream.
Nonmetals
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
Nonmetals
Oxides and Oxyacids• Nitric acid
Strong acid and oxidizer
Used in fertilizer and explosive production (TNT, nitrocellulose, nitroglycerine)
• Nitrous acidLess stable, yet
weaker acid than HNO3
Nonmetals
Other Group 5A Elements
This group contains nonmetals (N and P), a metal (Bi), and metalloids (As and Sb).
Nonmetals
Phosphorus
• Two allotropesWhite phosphorus
(P4)• Highly strained• Bursts into flames if
exposed to O2 in air
Red phosphorus• Very stable
Nonmetals
Oxyphosphorus Compounds
Phosphorus(III) oxide (P4O6) and phosphorus(V) oxide (P4O10) are anhydride forms of phosphorous (H3PO3) and phosphoric (H3PO4) acids
Nonmetals
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.
Nonmetals
Carbon
• Exists as four allotropes:GraphiteDiamondFullerenesCarbon nanotubules
• Graphite converted to diamond (at 100,000 atm and 3000C) for industrial uses
Nonmetals
Carbon Oxides• Carbon monoxide (CO)
Odorless, colorless gasBinds 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)
Nonmetals
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
Nonmetals
Silicon
• Second most abundant element in Earth’s crust
• Semiconductor used in making transistors and solar cells
• Purified by zone-refining
Nonmetals
Silicates
• Have a central silicon surrounded by 4 oxygens
• In disilicate, two tetrahedral structures share one oxygen
Silicate
Disilicate
Nonmetals
Silicates
• These units can further connect into sheets or strands.
• Talc and asbestos are two examples of molecules containing these structures.
Nonmetals
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.
Nonmetals
Boron
Borane anions, such as borohydride, BH4
-, are good reducing agents and sources of hydride ion.