Nonmetals

Chapter 22Chemistry of the

Nonmetals

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.

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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

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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

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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

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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)

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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

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Hydrides

• Three typesIonicMetallicMolecular

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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

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Metallic Hydrides

• Formed between hydrogen and transition metals, often in unusual ratiose.g., TiH1.8

• Retain electrical conductivity and other metallic properties

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Molecular Hydrides

• Formed between hydrogen and nonmetals or metalloids

• Usually gases or liquids at room temperature and normal atmospheric pressure

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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.

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Xenon Compounds

• Of all noble gases, Xe can be forced to form compounds most easily

• KrF2 also known, but decomposes at -10C

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Halogens

• Have outer electron configurations of ns2np5

• Large electron affinities and ionization energies

• Tend to accept one electron to form anion

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Halogens

• All have -1 oxidation state

• All but fluorine also have positive oxidation states up to +7 when bonded to more electronegative atoms

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Properties of Halogens

• Tend to be good oxidizers, due to their electronegativity

• Can oxidize anions of halides below them on periodic chart

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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

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Uses of Halogens

• Fluorine reacts to form fluorocarbon compounds used as lubricants, refrigerants and plastics.

• Teflon is a polymer of fluorocarbons.

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Uses of Halogens

• Chlorine is the most-used halogen.HClPlasticsBleachesWater purification

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Uses of Halogens

• Bromine is the anion for silver in photographic film.

• KI is added to table salt as a dietary supplement.

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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.

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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.

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Oxyacids and Oxyanions

• Oxyacid strength increases with increasing oxidation number of central halogen

• Oxyacids are strong oxidizers.• Oxyanions generally more stable than

corresponding acids

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Perchlorates

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

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Oxygen

• Joseph Priestley discovered oxygen in 1774.

• Lavoisier give it its name, which means “acid former.”

• Most commercial oxygen is obtained from air.

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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

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Uses of Oxygen

• Oxidizing agentBleach pulp and

paperMedical usesWelding (with

acetylene)

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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

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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.

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Peroxides

• Oxygen has oxidation state of -1

• O-O bond very weakDecomposition of

peroxides can be dangerously exothermic

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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

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Other Group 6A Elements

• Have oxidation states of -2 as well as several positive oxidation states

• Can have expanded octets

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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

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Sulfur

• Solid, yellow compound found in 8-membered ring

• As heated to melting, ring breaks and sulfur becomes viscous, reddish-brown liquid

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Sulfur

• Most sulfur used for H2SO4 and for vulcanization of rubber

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Pyrites

• Contain disulfide ion, S2

2-, the sulfur analog of peroxide

• Found in minerals like iron pyrite (fool’s gold)

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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.

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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

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Sulfur Oxides, Oxyacids, and Oxyanions

• Sulfuric acidStrong acidGood dehydrating agentDecent oxidizer

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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

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Nitrogen

• Discovered in 1772 by Daniel Rutherford

• Makes up 78% of Earth’s atmosphere

• Can exist in oxidation states from -3 to +5

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Nitrogen• Many nitrogen-

containing compounds strong oxidizers

• N2 made into NH3 in Haber processNH3 is

precursor to many other compounds

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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

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Oxides and Oxyacids

• Nitrous oxide (N2O; laughing gas) was the first general anesthetic.

• It is also used in aerosol products like whipped cream.

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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

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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

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Other Group 5A Elements

This group contains nonmetals (N and P), a metal (Bi), and metalloids (As and Sb).

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Phosphorus

• Two allotropesWhite phosphorus

(P4)• Highly strained• Bursts into flames if

exposed to O2 in air

Red phosphorus• Very stable

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Oxyphosphorus Compounds

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

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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.

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Carbon

• Exists as four allotropes:GraphiteDiamondFullerenesCarbon nanotubules

• Graphite converted to diamond (at 100,000 atm and 3000C) for industrial uses

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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)

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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

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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

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Silicates

• These units can further connect into sheets or strands.

• Talc and asbestos are two examples of molecules containing these structures.

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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.