Chapter 19Chapter 19

The Representative The Representative Elements: Groups 5A Elements: Groups 5A

Through 8AThrough 8A

Chapter 19: The Representative Elements Groups 5A Through 8A

19.1 The Group 5A Elements

19.2 The Chemistry of Nitrogen

19.3 The Chemistry of Phosphorous

19.4 The Group 6A Elements

19.5 The Chemistry of Oxygen

19.6 The Chemistry of Sulfur

19.7 The Group 7A Elements

19.8 The Group 8A Elements

Figure 19.1: Pyramidal shape of the Group 5A MX3 molecules

Figure 19.2: Trigonal bipyramidal shape of the MX5 molecules

Figure 19.3: Octahedral PF6-

Figure 19.4: Structures of the tetrahedral MX4+

and the octahedral MX6- ions

Figure 19.5: Inert atmosphere box

Source: Corbis

Many Binary Nitrogen compounds decompose exothermically to give the elements (Pg 893)

N2O(g) N2 (g) + ½ O2 (g) Ho = -82 kJ

NO(g) ½ N2 (g) + ½ O2 (g) Ho = -90 kJ

NO2 (g) ½ N2 (g) + O2 (g) Ho = -34 kJ

N2H4 (g) N2 (g) + 2 H2 (g) Ho = -95 kJ

NH3 (g) ½ N2 (g) + 3/2 H2 (g) Ho = +46 kJ

In This group of compounds only ammonia is endothermic in it’s Decomposition.

Nitroglycerine C3H5N3O9

H H H Nitroglycerine is prepared by very carefully nitrating glycerine in a mixedH C C C H nitrating acid bath consisting of concentrated nitric and sulfuric acids. O O O One must be very careful not to cause any sharp contact points or any sharp N N N blows to the compound, or it will explode. Any excess heating will cause O OO OO O immediate detonation as the reaction is very exothermic.The decomposition reaction is:

4 C3H5N3O9 (l) 6 N2 (g) + 12 CO2 (g) + 10 H2O(g) + O2 (g) + E

4 moles of nitroglycerine produces 29 moles of gaseous products

Trinitrotoluene (TNT) C7H5N3O6

CH3

NO2

NO2 NO2

Trinitrotoluene is a relatively stable explosive made nitrating toluene inthe same nitrating acids as nitroglycerine, but it is much more stable, will not detonate with out a strong shock, usually supplied with a blasting cap containing nitroglycerine.

The decomposition reaction for Trinitrotoluene is:

2 C7H5N3O6 (s) 12 CO(g) + 5 H2 (g) + 3 N2 (g) + 2 C(s) + E

2 moles of TNT produce 20 moles of gaseous products

Figure 19.6: Schematic diagram of the Haber process for the manufacture of ammonia.

Figure 19.7: Nitrogen cycle

Nodules on the roots of pea plants contain nitrogen-fixing bacteria.

Source: Photo Researchers, Inc.

Figure 19.8: Molecular structure of hydrazine (N2H4)

Blowing agents--such as hydrazine, which forms nitrogen gas on decomposition--are used to produce porous plastics like these

polystyrene products.

Copper penny reacts with nitric acid to produce NO gas, which is immediately oxidized in air to give reddish brown NO2

-.

Source: Fundamental Photographs

Figure 19.9: Molecular orbital energy-level diagram for nitric oxide (NO).

Kissing bug

Source: Photo Researchers, Inc.

Three-dimensional complex nitrohphorin-1

Source: Department of Biochemistry, University of Arizona, Tuscon

Figure 19.10: Ostwald process

Figure 19.11: (a) molecular structure of HNO3 (b) resonance structure

White phosphorous reacts vigorously with the oxygen in air and must be stored under water.

Red phosphorus is stable in air.

Source: Stock Boston

Figure 19.12: (a) P4 molecule found in white phosphorous (b) crystalline network structure of black Phosphorous (c) chain structure of

red phosphorous

White Black Red

Phosphorous

Figure 19.13: Structures of P4O6 and P4O10

Lewis structure and Molecular model of Phosphoric acid (H3PO4)

H—O—P—O—H

O

H

O

..

......

.. .... ..

Figure 19.14: Structures of (a) phosphorus acid (H3PO3), and (b) hypophosphorous acid (H3PO2)

Phosphorous in Fertilizers

Phosphorous is one of the essential elements for life, and is required in Fertilizers for plants to grow.

Super phosphate of lime: CaSO4 2 H2O and Ca(H2PO4)2 H2O

Triple phosphate: Ca(H2PO4)2

Reaction of Ammonia and Phosphoric acid gives ammonium dihydrogen phosphate: (NH4)H2PO4

This compound not only has phosphorous, but Nitrogen as well.

Phosphorous HalidesThe general formulas are PX3 and PX5

PF3 is a gas PCl3 is a liquid ( bp = 74oC) PBr3 is a liquid (bp = 175oC) PI3 is an unstable red solid (mp = 61oC)

PX3 + 3 H2O(l) H3PO3 (aq) + 3 HX(aq)

PCl5 is an ionic solid of : PCl6- and PCl4+ ions.

PBr5 is an ionic solid of : PBr4+ and Br - ions.

The PX5 compounds react with water to form Phosphoric acid.

PX5 + 4 H2O(l) H3PO4 (aq) + 5 HX(aq)

Figure 19.15: Structures of the phosphorous halides (a) PX3 compounds have

pyramidal molecules (b) the gaseous and liquid phases of PX5 compound are trigonal

bipyramidal molecules

Important Reactions of the Nitrogen Family - I

1.Nitrogen is “fixed” industrially in the Haber process:

Further reactions convert NH3 to NO, NO2, and HNO3. Some other group hydrides are formed from reaction in water (or H3O+) of metal phosphide, arsenide, and so forth:

2. Halides are formed by direct combination of the elements:

3.Oxoacids are formed from the halide with a reaction in water that is common to many nonmetal halides:

N2 (g) + 3 H2 (g) _______________

Ca3P2 (s) + 6 H2O(l) ____________________________

2 M(s) + 3X2 (-) 2 MX3 (-) (M = all except N)

MX3 (-) + X2 (-) MX5 (-) (M = all except N and Bi)

MX3 (-) + 3 H2O(l) ______________________ ( M = all except N)

Important Reactions of the Nitrogen Family - II

3. continued:

Note that the oxidation number of element does not change.

4. Phosphate ions are dehydrated to form polyphosphates:

5. When P4 reacts in basic solution, its oxidation state both decreases and increases:

Analogous reactions are typical of many nonmetals, such as S8 and X2.

MX5 (-) + 4 H2O(l) ____________________________ M = all except N and Bi)

3 NaH2PO4 (s) ___________________________

P4 (s) + 3 OH-(aq) + 3 H2O(l) PH3 (g) + 3 H2PO2

-(aq)

Important Compounds in the Nitrogen Family - I

1. Ammonia, NH3. First substance formed when atmospheric N2 is used to make N - containing compounds. Annual multimillion - ton production for use in fertilizers, explosives, rayon, and polymers such as nylon, urea-formaldehyde resins, and acrylics.2. Hydrazine, N2H4. Nitrogen’s other hydride. Used in rockets as a propellant, and as a starting point for antituberculin drugs.3. Nitric oxide (NO), nitrogen dioxide (NO2), and nitric acid (HNO3). Oxides are intermediates to HNO3. Acid used in fertilizer manufacture, nylon production, metal etching, and explosives industry.4. Amino acids, H3N+-CH(R)-COO- (R = one of 20 different organic groups). Occur in every organism, both free and linked together into proteins. Essential to growth and function of all cells. Synthetic amino acids used as dietary supplements.

Important Compounds in the Nitrogen Family-II

5. Phosphorous trichloride, PCl3. Used to form many organic phosphorous compounds, including oil and fuel additives, plasticizers, flame retardants, and insecticides. Also used to make PCl5, POCl3, and other important P-containing compounds.6. Tetraphosphorous decoxide (P4O10) and phosphoric acid (H3PO4) Many uses, and probably the most important P chemicals.7. Sodium triphosphate, Na5P3O10. As a water-softening agent (Calgon), combines with hard-water Mg2+and Ca2+ ions, preventing them from reacting with soap anions, and thus improves cleaning action. Use curtailed in the United States because it pollutes lakes and streams by causing excessive algae growth.8. Adenosine triphosphate (ATP) and other biophosphates. ATP acts to transfer chemical energy in the cell; necessary for all biological processes requiring energy. Phosphate groups occur in sugars, fats, proteins, and nucleic acids.9. Bismuth subsalicylate, BiO(C7H5O3). The material in Pepto-Bismol.

The Stepwise Ionization & Neutralization of Phosphoric Acid

H3PO4 (aq) + H2O(l) H2PO4- (aq) + H3O+

(aq)

H2PO4-(aq) + H2O(l) HPO4

-2(aq) + H3O+

(aq)

HPO4-2

(aq) + H2O(l) PO4-3

(aq) + H3O+(aq)

H3PO4 (aq) + 3 H2O(l) PO4-3

(aq) + 3 H3O+(aq)

H3PO4 (aq) + NaOH(aq) NaH2PO4 (aq) + H2O(l)

NaH2PO4 (aq) + NaOH(aq) Na2HPO4 (aq) + H2O(l)

Na2HPO4 (aq) + NaOH(aq) Na3PO4 (aq) + H2O(l)

H3PO4 (aq) + 3 NaOH(aq) Na3PO4 (aq) + 3 H2O(l)

Walnuts contain trace amounts of selenium.

Source: Alamy Images

U.S. Navy test pilot in an F-14 jet using an oxygen mask.

Source: Photo Researchers, Inc.

Sources of Sulfur on Earth

Elemental Sulfur is found on the Earth in:

Volcanic deposits – Fumaroles Underground deposits

Common Minerals containing Sulfur

PbS – Galena HgS – Cinnabar FeS2 – Pyrite CaSO4 2 H2O – Gypsum MgSO4 7 H2O – Epsomite Na2SO4 CaSO4 - Galberite

Figure 19.16: Frasch method for recovering sulfur from underground deposits.

Melted sulfur obtained from underground deposits by the Frasch process.

Source: Photo Researchers, Inc.

Figure 19.17: (a) the S8 molecule (b) chains of sulfur atoms in viscous liquid sulfur. The chains may contain as many as

10,000 sulfur atoms.

Source: Color-Pic, Inc. Crystals of monoclinic sulfur

Crystals of rhombic sulfur

Pouring liquid sulfur into water to produce plastic sulfur.

Source: American Color

Figure 19.19: (a) Two resonance structures for SO2 (b) The SO2 molecule is a bent

molecule as predicted by the VSEPR model

Figure 19.20: (a) The resonance structures most commonly given for SO3 (b) a resonance structure with three double bonds (c) SO3 is a

planar molecule with three equal bonds

Figure 19.21: Different structures for solid SO3

S3O9 rings

(SO3)x chains

In both cases the sulfur atomsare surrounded by a tetrahedralarrangement of oxygen atoms.

Oxyacids of sulfur

There are two important Oxyacids of sulfur, they are formed by The reaction of the oxides of sulfur with water.

SO2 (g) + H2O(g) H2SO3 (aq) Sulfurous acid

H2SO3 (aq) + H2O(l) H3O+(aq) + HSO3

-(aq) Ka1 = 1.5 x 10-2

HSO3-(aq) + H2O(l) H3O+

(aq) + SO3-2

(aq) Ka2 = 1.0 x 10-7

SO3 (g) + H2O(l) H2SO4 (aq) Sulfuric acid

H2SO4 (aq) + H2O(l) H3O+(aq) + HSO4

-(aq) Ka1 = Large

HSO4-(aq) + H2O(l) H3O+

(aq) + SO4-2

(aq) Ka2 = 1.2 x 10-2

Figure 19.22: Reaction of H2SO4 with sucrose to produce a blackened column of carbon.

Figure 19.23: Structures of (a) SF4 (b) SF6 (c) S2F10 (d) S2CL2

SF4 SF6S2F10 S2Cl2

Important Reactions of the Oxygen Family - I

1. Halides are formed by direct combination:

2. The other elements in the group are oxidized by O2:

SO2 is oxidized further, and the product is used in the final step of H2SO4 manufacture.

M(s) + X2 (g) various halides

(M = S, Se, Te ; X = F, Cl)

M(s) + O2 (g) MO2 (-) (M = S, Se, Te, Po)

2 SO2 (g) + O2 (g) _________

SO3 (g) + H2O(l) ___________

Important Reactions of the Oxygen Family - II

3. Sulfur is recovered when hydrogen sulfide is oxidized:

This reaction is used to obtain sulfur when natural deposits are not available.

4. The thiosulfate ion is formed when an alkali sulfite reacts with sulfur, as in the preparation of photographer’s “hypo”:

8 H2S(g) + 4 O2 (g) _____________________

S8 (s) + 8 Na2SO3 (aq) ______________________

Important Compounds of the Oxygen Family - I

1. Water, H2O. The single most important compound on earth!2. Hydrogen peroxide, H2O2. Used as an oxidizing agent, disinfectant, bleach, and in the production of peroxy compounds for polymerization.3. Hydrogen sulfide, H2S. Vile-smelling toxic gas formed during anaerobic decomposition of plant and animal matter, in volcanoes, and in deep sea thermal vents. Used as a source and in the manufacture of paper. Atmospheric traces cause silver to tarnish through formation of black Ag2S.4. Sulfur dioxide, SO2. Colorless, choking gas formed in volcanoes or whenever an S-containing compound (coal, oil, metal sulfide ores, and so on) is burned. More than 90% of SO2 produced is used to make sulfuric acid. Also used as a fumigant and preservative of fruit, syrups, and wine. As a reducing agent, removes excess Cl2 from industrial waste water, removes O2 from petroleum handling tanks, and prepares ClO2 for bleaching paper. Major atmospheric pollutant in acid rain.

Important Compounds of the Oxygen Family - II

5. Sulfur trioxide (SO3) and sulfuric acid (H2SO4). SO3 , formed from SO2 over V2O5 catalysts, is then converted to sulfuric acid. The acid is the cheapest strong acid and is so widely used in industry that its production level is an indicator of a nation’s economic strength. Strong dehydrating agent that removes water from any organic source.6. Sulfur hexafluoride, SF6. Extremely inert gas used as an electrical insulator. Also used as an atmospheric tracer of air movement over extremely great distances.

O - S - Se - Te - Po

Gaseous Liquid SolidChlorine Bromine Iodine

Candle burning in an atmosphere of Cl2(g).

Source: Phototake

Figure 19.24: Hydrogen bonding among HF molecules in liquid hydrogen fluoride.

Figure 19.25: Structures of the oxychloro anions.

Figure 19.26: Idealized structures of the interhalogens CIF3 and IF5.

Halogen Oxides, Oxoacids and Oxoanions

Production of chlorine dioxide:

2 NaClO3 (s) + SO2 (g) + H2SO4 (aq) _____________________

Preparation of dichlorine heptaoxide by the condensation of perchloric acid:

O3Cl OH + HO ClO3 H2O(l) + O3Cl O ClO3 (l)

Decomposition of chlorates to give oxygen:

2 KClO3 (s) _______________________

Ammonium perchlorate and Al used in the space shuttle boosters:

10 Al(s) + 6 NH4ClO4 (s) 4 Al2O3 (s) + 12 H2O(g) + 3 N2 (g) + 2 AlCl3 (g)

Important Reactions of the Halogens - I

1. The halogens (X2) oxidize many metals and non-metals. The reaction with hydrogen, although not used commercially for HX production (except for high-purity HCl), is characteristic of these strong oxidizing agents.

2. The halogens disproportionate in water:

In aqueous base, the reaction goes to completion to form hypohalites and, at higher temperatures, halates; for example:

X2 (-) + H2 (g) ______________

X2 (-) + H2O(l) ___________________ X = Cl, Br, I

3 Cl2 (g) + 6 OH-(aq) _________________________

Important Reactions of the Halogens - II

3. Molecular Fluorine, F2 is produced electrolytically at moderate temperature:

A major use of F2 is in the preparation of UF6 for nuclear fuel.

4. Glass (amorphous silica) is etched with HF:

2HF (as KHF2, a solution of KF in HF) H2 (g) + F2 (g)

SiO2 (s) + 6 HF(g) ______________________

F - Cl - Br - I - At

Important Compounds of the Halogens - I

1. Fluorspar (fluorite), CaF2. Widely distributed mineral used as a flux in steel making and in the production of HF.

2. Hydrogen fluoride, HF. Colorless, extremely toxic gas used to make F2, organic fluorine compounds, and polymers. Also used in aluminum manufacture and in glass etching.

3. Hydrogen chloride, HCl. Extremely water-soluble gas that forms hydrochloric acid, which occurs naturally in stomach juice of mammals (humans produce 1.5L of 0.1 M HCl daily) and in volcanic gases (from reaction of H2O on sea salt). Made by reaction of NaCl and H2SO4 and as a by-product of plastics (PVC) production. Used in the “pickling” of steel (removal of adhering oxides) and in the production of syrups, rayon, and plastic.

Important Compounds of the Halogens - II

4. Sodium hypochlorite, NaClO, and calcium hypochlorite, Ca(ClO)2. Oxidizing agents used to bleach wood pulp and textile, and disinfect swimming pools, foods, and sewage (also used to disinfect the Apollo 11 on return from the moon). Household bleach is 5.25% NaClO by mass in water.5. Ammonium perchlorate, NH4ClO4. Strong oxidizing agent used in the space shuttle program.6. Potassium iodide, KI. Most common soluble iodide. Table salt additive to prevent thyroid disease (goiter). Used in chemical analysis because it is easily oxidized to I2, which forms a colored end point.7. Polychorinated biphenyls, PCBs. Mixture of chlorinated organic compounds used as nonflammable insulating liquids in electrical transformers. Production discontinued due to persistence in the environment, where it becomes concentrated in fish, birds, and mammals, and causes reproductive disturbances and possibly cancer.

Figure 19.27: Structures of several known xenon compounds

Neon sign maker and artist Jess Baird shows off a few of the items he has made in his

Weatherford, Texas, shop.

Source: AP/Wide World Photos

Crystals ofXenontetrafluoride (XeF4)

The Periodic Table of the ElementsH

Li Be

NaMg

K Ca Sc

Rb

Cs

Fr

Sr

Ba

Ra

Ti V CrMn Fe

Y

La

Ac

Co Ni Cu Zn

Zr

Hf

Nb

Ta

Rf Du Sg

Mo

W

Tc

Re

Ru

Os

Rh

Ir

Pd

Pt

Ag

Au

Cd

Hg

B C N O F

He

Ne

ArAl Si P S Cl

Ga Ge As Se Br Kr

Xe

Rn

ITe

At

Sb

PoBi

SnIn

PbTl

Ce Pr Nd Pm

Th

SmEu Gd Tb Dy Ho Er Tm Yb Lu

Pa U Np PuAmCm Bk Cf Es FmMd No Lr

Bo HaMe

Elements that are polyatomic in their natural state

Diatomic

Tetratomic ( 4 atoms per molecule)

Octatomic ( 8 atoms per molecule)