Transcript student_chap19

Chapter 19
The Representative
Elements: Groups 5A
Through 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
Nitroglycerine is prepared by very
carefully nitrating glycerine in a mixed
H 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)
H
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
Trinitrotoluene is a relatively stable
explosive made nitrating toluene in
the 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.
NO2
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
Phosphorous
Red
Figure 19.13: Structures of P4O6 and P4O10
Lewis structure and Molecular model of
Phosphoric acid (H3PO4)
..
..
O
..
..
H—O—P—O—H
..
..
..
..
O
H
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 Halides
The 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:
N2 (g) + 3 H2 (g)
_______________
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:
Ca3P2 (s) + 6 H2O(l)
____________________________
2. Halides are formed by direct combination of the elements:
2 M(s) + 3X2 (-)
2 MX3 (-)
(M = all except N)
MX3 (-) + X2 (-)
MX5 (-)
(M = all except N and Bi)
3.Oxoacids are formed from the halide with a reaction in water that is
common to many nonmetal halides:
MX3 (-) + 3 H2O(l)
______________________
( M = all except N)
Important Reactions of the Nitrogen Family - II
3. continued:
MX5 (-) + 4 H2O(l)
____________________________
M = all except N and Bi)
Note that the oxidation number of element does not change.
4. Phosphate ions are dehydrated to form polyphosphates:
3 NaH2PO4 (s)
___________________________
5. When P4 reacts in basic solution, its oxidation state both decreases
and increases:
P4 (s) + 3 OH-(aq) + 3 H2O(l)
PH3 (g) + 3 H2PO2-(aq)
Analogous reactions are typical of many nonmetals, such as S8 and X2.
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.
Crystals of rhombic
sulfur
Source: Color-Pic, Inc.
Crystals of monoclinic 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
In both cases the sulfur atoms
are surrounded by a tetrahedral
arrangement of oxygen atoms.
(SO3)x chains
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
SF6
S2F10
S2Cl2
Important Reactions of the Oxygen Family - I
1. Halides are formed by direct combination:
M(s) + X2 (g)
various halides
(M = S, Se, Te ; X = F, Cl)
2. The other elements in the group are oxidized by O2:
M(s) + O2 (g)
MO2 (-)
(M = S, Se, Te, Po)
SO2 is oxidized further, and the product is used in the final step of
H2SO4 manufacture.
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:
8 H2S(g) + 4 O2 (g)
_____________________
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”:
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
Chlorine
Liquid
Bromine
Solid
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.
X2 (-) + H2 (g)
______________
2. The halogens disproportionate in water:
X2 (-) + H2O(l)
___________________
X = Cl, Br, I
In aqueous base, the reaction goes to completion to form hypohalites
and, at higher temperatures, halates; for example:
3 Cl2 (g) + 6 OH-(aq)
_________________________
Important Reactions of the Halogens - II
3. Molecular Fluorine, F2 is produced electrolytically at moderate
temperature:
2HF (as KHF2, a solution of KF in HF)
H2 (g) + F2 (g)
A major use of F2 is in the preparation of UF6 for nuclear fuel.
4. Glass (amorphous silica) is etched with HF:
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 of
Xenon
tetrafluoride
(XeF4)
The Periodic Table of the Elements
H
Elements that are polyatomic
Li Be
B C N
in their natural state
NaM
Al Si P
K gCa Sc Ti V CrMn Fe Co Ni Cu Zn Ga Ge As
Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb
He
O F Ne
S Cl Ar
Se Br Kr
Te I Xe
Cs Ba La H Ta W Re O Ir Pt Au Hg Tl Pb Bi Po At Rn
Fr R Ac fRf Du Sg Bo sHaMe
a
Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu
Th Pa U Np PuAmC Bk Cf Es FmMd No Lr
m
Diatomic
Octatomic ( 8 atoms
per molecule)
Tetratomic ( 4 atoms
per molecule)