Groups%205A%20

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Groups 5A 8A
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Group 5A

• Nitrogen and phosphorus are non-metals, arsenic
  is a semimetal, and antimony and bismuth tend to
  be metallic, typically forming ions with a 3
  charge.
• The oxides of nitrogen and phosphorus are
  acidic when dissolved in water. Arsenic and
  antimony oxides are amphoteric, and bismuth oxide
  is basic.

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Group 5A

• The elements of group 5A may form three, five
  or six covalent bonds, except for nitrogen which
  cannot expand its octet.
• Due to its small size, nitrogen readily forms p
  bonds. Thus elemental nitrogen, N2, has a triple
  bond. The other elements exist as larger
  molecules containing single bonds.

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Nitrogen

• Elemental nitrogen is an extremely stable
  molecule due to the triple bond. As a result,
  many nitrogen containing compounds decompose
  exothermically (and sometimes explosively) to
  form nitrogen gas.

5
Explosives

• Nitrogen based explosives such as
  nitroglycerin, will rapidly decompose when
  ignited or exposed to a sudden impact.

6
Explosives

• C3H5(NO3)3(l) ? 6 N2(g) 12CO2(g)
  12H2O(g) O2(g) energy
• Note the large number of moles of gaseous
  products. Explosives typically involve a very
  large volume change, producing many moles of
  small gaseous molecules.

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Explosives

• Trinitrotoluene, TNT, is another nitrogen based
  explosive.
• 2C7H5(NO3)3(l) ? 12 CO2(g) 5 H2(g)
  3N2(g) 2C(s) energy

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Sodium Azide

• Sodium azide, NaN3(s), is used in air bags in
  automobiles. A small amount of sodium azide
  (100g) yields 56L of nitrogen gas at 25oC and 1
  atm.

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Sodium Azide

• NaN3(s) ? 2Na(l) 3 H2(g)
• This reaction takes place in about 40ms. Other
  components are put in the air bag so that the
  molten sodium metal is deactivated into glassy
  silicates.
• 10 Na(l) 2KNO3(s) ?K2O(s) 5Na2O(s) N2(g)
• 2 K2O(s) SiO2(s) ? K4SiO4(s)
• 2 Na2O(s) SiO2(s) ? Na4SiO4(s)

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Nitrogen Fixation

• Bacteria (in the nodules on the roots of pea
  plants) can readily convert nitrogen to ammonia
  at 1 atm and soil temperature.
• The Haber process requires a temperature of
  400oC and a pressure of 250 atm.

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Uses of Nitrogen Compounds

• Ammonia, synthesized from nitrogen and hydrogen
  using the Haber process, is used to make
  fertilizers, explosives and nitric acid.
• Dinitrogen oxide, N2O, is used as laughing
  gas, a dental anesthetic. The gas is highly
  soluble in fats, and its major use is as a
  propellant in cans of whipped cream.

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Uses of Nitrogen Compounds

• Nitrogen monoxide, NO, is a biologically active
  molecule, and is crucial in controlling blood
  pressure and the dilation of blood vessels.

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Environmental Issues

• Nitrogen dioxide (NO2) and dinitrogen
  tetra-oxide (N2O4) are in equilibrium with each
  other
• N2O4(g) ? 2 NO2(g)
• colorless red-brown
• The oxides of nitrogen are the result of high
  temperature combustion in jet engines and
  automobiles.

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Environmental Issues

• The compounds cause the reddish brown smog seen
  over Los Angeles and other cities on a sunny day.
  They also react with moisture in the air to
  produce nitric acid and nitrous acid.
• This acid rain is a respiratory irritant, and
  destroys facades of buildings and statuary.

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Isolation of Phosphorus

• Phosphorus was initially isolated in an
  attempt to extract gold from urine.
• The element emits light and glows when exposed
  to oxygen.

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Phosphorus

• Elemental phosphorus exists as several
  allotropes. All differ greatly in structure from
  nitrogen due to a lack of multiple bonding
  between the larger phosphorus atoms.
  Phosphorous can also use d orbitals to expand
  its bonding.

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Elemental Phosphorus
white phosphorus
black phosphorus
red phosphorus
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Elemental Phosphorus
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White Phosphorus

• White phosphorus exists as discrete P4
  molecules. It is a waxy white solid that is very
  poisonous and reactive. It burns vigorously in
  air, and is stored under water.

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White Phosphorus

• The element gets its name from the
  phosphorescent glow emitted by white phosphorus
  when it is exposed to air in the dark.
• White phosphorus has been used in weaponry.
  The pieces of phosphorus in bombs and grenades
  get embedded in the skin, where they burn.

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Red Phosphorus

• Red Phosphorus is a polymeric chain of P4 units.
  It is stable in air to a temperature of 400oC.
  Red phosphorus is used in safety matches on the
  striking surface.

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Red Phosphorus

• Red phosphorus is used in safety matches on
  the striking surface.

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Black Phosphorus

• Black phosphorus is the most stable of the
  allotropes. It is formed from white phosphorus
  that is heated under very high pressures.

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Source of Phosphorus

• Phosphorus must be extracted from its
  compounds, as it is not found in elemental form.
  The main source is phosphate rock, or calcium
  phosphate. Large deposits are found in central
  Florida, Morocco and the Pacific island of Nauru.
• The extraction process consumes large amounts
  of electricity and coke, and produces large
  amounts of dusts, flue gases and sludge.

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Uses of Phosphorus Compounds

• Phosphates are used in fertilizers, and the
  salt of tripolyphosphoric acid is used in
  detergents that wont form insoluble scum in
  hard water.
• Phosphoric acid is added to soft drinks where
  it prevents bacterial growth and also forms inert
  compounds with any metal ions that may be leached
  from the container walls.

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Biological Aspects - Nitrogen

• All plant life requires nitrogen for growth and
  survival. Bacteria found in nodules on the roots
  of pea, bean, alder and clover plants convert
  nitrogen in the air to nitrogen compounds.

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Biological Aspects - Phosphorus

• Phosphorus is essential for life. The hydrogen
  phosphate ion and dihydrogen phosphate ions are
  involved in buffering blood. Phosphate units
  link the sugar esters of DNA and RNA, and also
  make up part of ATP, the energy storage unit in
  living things.

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Biological Aspects - Arsenic

• Arsenic, though generally considered toxic, is
  also essential to life. We only need trace
  amounts, and its role is still unknown.
• In the 19th century, before the discovery of
  antibiotics, arsenic was used as one of the first
  forms of chemotherapy to destroy the organism
  that causes syphilis.

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The group 6A Elements

• Group 6A, oxygen, sulfur, selenium , tellurium
  and polonium, are sometimes called the
  chalcogens. O, S and Se are nonmetals, Te a
  semimetal, and polonium the only metal of the
  group.
• Except for oxygen, the other members of the
  group exhibit all even-numbered oxidation states
  from -2 through zero to 6.

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Oxygen

• Oxygen contains a double bond that is much
  stronger than a single bond (494 kJ/mol vs. 142
  kJ/mol). The lower elements in the group form
  much weaker p bonds due to their larger atomic
  size and greater bond length.

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Oxygen

• Oxygen is a colorless, odorless gas that forms
  a pale blue liquid. The molecule is paramagnetic
  due to the presence of two unpaired electrons,
  and is attracted to a magnetic field.

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Ozone

• Ozone, O3, is an allotrope of oxygen. It
  occurs naturally in the upper atmosphere of
  earth. The ozone layer absorbs ultraviolet light
  and serves to help screen out harmful, cancer
  causing, radiation.

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Sulfur

• Sulfur is found in large deposits as the free
  element, or in a variety of ores. Elemental
  sulfur has a variety of forms and structures. At
  room temperature, the most stable form is rhombic
  sulfur, S8 rings.

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Sulfur

• If molten sulfur is cooled slowly, the eight-
  membered rings stack into monoclinic sulfur,
  which has a needle-like appearance.

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The Frasch Process

• The Frasch process is used to extract sulfur
  from underground deposits. Superheated water
  (under pressure) is pumped into the ground where
  the sulfur melts. The molten sulfur is then
  pumped up to the surface and into huge forms
  where it cools and solidifies. Explosives are
  used to break the huge chunks of sulfur into more
  useable sizes.

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The Frasch Process
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The Frasch Process
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Sulfur Oxides

• Sulfur dioxide and sulfur trioxide are formed
  during the combustion of sulfur-containing fuels
  (coal). They are respiratory irritants, and,
  when combined with moisture in the air, produce
  acid rain.

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Selenium

• Until the 1960s, the only major use of selenium
  was the addition of CdSe to glass to produce a
  ruby-red color. Cadmium selenide is also used as
  a semiconductor in photocells, because its
  conductivity varies with light intensity.

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Selenium

• Selenium is now used in xerox machines and
  laser printers. They use a drum coated with
  selenium that is exposed to an electric field.
  The regions on the drum that are exposed to high
  light intensity lose their charge. Toner powder
  adheres only to the charged areas of the drum
  which correspond to the printed areas on the page.

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Photocopiers
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The Halogens Group 7A
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Group 7A

• Group 7A is the first group that consists of
  all non-metals. Fluorine, chlorine, bromine and
  iodine all exist as diatomic molecules at room
  temperature. Astatine, At, is unstable, and very
  rare.
• The elements illustrate a variety of group
  trends.

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Group 7A
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Group 7A

• The halogens are typically found in ionic form.
  The elements are prepared by electrolysis of
  salts (for F2 and Cl2) or using redox reactions.

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Fluorine

• Fluorine is the most electronegative element,
  and often acts as an oxidizing agent. Fluorine
  exhibits oxidation numbers of zero and -1 only.
  The other halogens have positive oxidation
  numbers when bonded to fluorine or oxygen.

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Fluorine

• Fluorine has only one isotope, 19F. F2(g) is
  used to separate isotopes of uranium. Uranium
  exists as two isotopes, 238U and 235U.
  Uranium-235 is used in bombs and nuclear
  reactors. Both isotopes of uranium are found in
  deposits as UO2(s).

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Fluorine

• The uranium (IV) oxide is converted to the
  fluoride using HF(g).
• UO2(s) 4 HF(g) ? UF4(s) 2 H2O(g)

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Fluorine

• The ionic UF4 is reacted with fluorine gas to
  form covalent (and gaseous at 60oC) UF6.
• UF4(s) 2 F2 (g)? UF6(g)
• The gaseous mixture of 235UF6 and 238UF6 can be
  separated based on their different rates of
  effusion.

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Hydrofluoric Acid

• HF(aq), is a weak acid, whereas the binary
  acids of the other halogens are all strong acids.
  HF has another unique property. It can be used
  to etch glass, and must be stored in plastic
  bottles.

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Hydrofluoric Acid

• SiO2(s) 6 HF(aq)? SiF62-(aq) 2 H(aq)
• 2 H2O(l)

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Fluoridation of Water

• The enamel of teeth contains hydroxyapatite,
  Ca5(PO4)3(OH). The compound is somewhat soluble
  in the acidic media of the mouth. If the
  hydoxide ion is replaced with fluoride, the less
  soluble and harder fluorapetite, Ca5(PO4)3(F) is
  formed. The harder enamel resists decay.

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Chlorine

• Chlorine is a pale green poisonous gas, and was
  used as the first poison gas in warfare. In
  small doses, chlorine gas effectively kills
  harmful bacteria in drinking and swimming water.

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Chlorine

• Chlorine is a pale green poisonous gas, and was
  used as the first poison gas in warfare. In
  small doses, chlorine gas effectively kills
  harmful bacteria in drinking and swimming water.

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Bromine

• Bromine is a volatile, oily, orange-brown
  corrosive liquid at room temperature. Silver
  bromide, AgBr(s), is used in black and white
  photography. Upon exposure to light, the silver
  ion forms fine crystals of metallic silver.

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Iodine

• Iodine is a dark purple metallic looking solid.
  In the human body, it is found primarily in the
  thyroid gland where if is used in the synthesis
  of the hormones thyroxine and triiodothyronine.
  These hormones are essential for growth, the
  regulation of neuromuscular functions, and the
  maintenance of reproductive functions.

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Group 8A The Noble Gases
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Group 8A The Noble Gases

• It was believed that the noble gases, He, Ne,
  Ar, Kr, Xe and Rn, were inert, and never formed
  compounds. During the past 50 years, several
  compounds of Kr, Ze and Rn have been synthesized.
  

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The Discovery of the Noble Gases

• It had been known since at least 1785 that air
  contained something in addition to oxygen and
  nitrogen. The new elements was called argon,
  from the Greek word for lazy.
• Helium was identified in the emission spectrum
  of the sun (1868) before it was isolated on earth
  from uranium ores.

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Group Trends

• All elements are odorless, colorless monatomic
  gases at room temperature. The boiling points
  are consistent with weak london dispersion forces
  and the increase in polarizability going down the
  group.

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Group 8A The Noble Gases

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Uses of the Noble Gases

• Helium, due to its low density and chemical
  inertness, is used to provide lift for baloons
  and blimps.
• Helium is also used in breathing mixtures for
  deep sea diving. It is less soluble in the blood
  than nitrogen, and thus minimizes the bends.

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Uses of Noble Gases

• Argon is chiefly used to provide an inert
  atmosphere for chemical reactions and in welding.
  Along with Ne, Kr and Xe, argon also produces
  characteristic colors in neon lights. Argon is
  also used between panes of glass in thermal
  insulating windows.

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Compounds of Xe and Kr

• The first compound of a noble gas, XePtF6(s),
  was synthesized in the early 1960s using a very
  strong oxidizing agent, PtF6(g).
• Since then, several compounds containing Xe or
  Kr with fluorine and oxygen have been
  synthesized.

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Radon

• Radon is radioactive, and is formed in rocks
  and soil by the radioactive decay of uranium and
  thorium. 222Rn can infiltrate the air in
  basements. Since it is gaseous, it is breathed
  into the lungs where it undergoes radioactive
  decay, bombarding lung tissue with alpha and beta
  particles. These particles disrupt living cells
  and can initiate lung cancer.