1 group 16- the calcogens - o, s, se, nonmetals; te, metalloid; and po metal - have multiple...
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Group 16- The Calcogens- O, S, Se, Nonmetals; Te, metalloid; and Po metal- Have multiple allotropes: Oxygen is a gas as O2 or O3; Sulfur is a
Gas as S2 S3 S4 Solid as S5 to S8 are cyclic molecules. Selenium is a solid in either Se8 or polymeric form
- Unpleasant odours- Form one monoatomic anion (-2)
Po2+ and Po4+ also exist (radio active)- Six valence electrons: [N.G.] ns2 np4
- Large negative ΔHelectronic attraction
Melting Point
Boiling Point
State (at 20 °C)
Density (at 20 °C)
Oxygen -192.5 °C -111 °C Gas 0.00143 g/cm3
Sulfur 113 °C 445 °C Solid 2.07 g/cm3
Selenium 221 °C 685 °C Solid 4.79 g/cm3
Tellurium 450 °C 1390 °C Solid 6.24 g/cm3
Polonium 254 °C 962 °C Solid 9.32 g/cm3
Oxygen
• “oxygen”, typically diatomic oxygen (O2),
• Phases of matter:• Gas: colourless, odourless,
tasteless • Liquid: pale blue explosive liquid.
Solid: pale blue and very explosive.
• Reactions
• Strong oxidizing agent.
• Reacts spontaneously with the metals of groups 1, 2 and 13; as well as some transition metals.
• Some of these reactions are quite slow unless heat or a catalyst is added. Why?
• Another way to increase the reactivity of gaseous O2 is to add water. Iron rusts much more quickly in damp air than in dry air!
Photo by the US EPA
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Ozone• - Ozone (O3) - a significant component
of “smog”; • - essential component
of the upper atmosphere.
• - Ozone is formed from O2 in an endothermic reaction:
This reaction requires a large input of energy, i.e., from an electric current
or electromagnetic radiation from the sun.
• - Ozone is unstable, decomposing to oxygen (O2). In order to maintain
• constant amount of ozone, it must
• continually be regenerated.
• - Printer and photo copiers produce ozone
• Health hazard
• - Used as in swimming pools
Photo by the US EPA
Atmospheric Ozone• - Ozone absorbs UV
protecting organisms significant
• DNA damage. • -Ozone is broken into O2
and oxygen free radical• which reacts ozone to form
O2.
• -This isan exothermic process helping to moderate
• the Earth’s temperature.• S. Rowland and M. Molina in
1974 first reported that• atmospheric ozone was
disappearing wining them• The Nobel Prize in
Chemistry in 1995.
• -The “Ozone Hole” in the Antarctic was first reported
• in 1985 by J. Farman, B. Gardiner, and J. Shanklin.
- The “hole in the ozone layer” is an area in which the ozone has thinnedsubstantially. 70% of the ozone
over the Antarctic and 30% of the ozone over the Arctic had disappeared by the early 1980s!
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Where is the ozone going?– Chlorofluorocarbons (CFCs) used as refrigerants – accelerate the– decomposition of ozone to O2.
1) the CFC absorbs UV radiation to give a free chlorine atom as a “free radical”
2) This chlorine atom reacts with ozone to form O2 and ClO.
– 3) The ClO reacts with a free oxygen atom to form more O2 and regenerate the chlorine atom.
– This cycle continues until the chlorine atom finds something to react
– with other than ozone. That means that one polluted CFC molecule
– can be responsible for the destruction of millions of ozone molecules!
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Sulfur• Sulfur exists as a wide range of
allotropes:– S2 is violet– S3 is blue– S4 is red– S5 is red-orange– S6 is yellow-orange– S7 to S15 are all shades of yellow as are S18, S20 – & S (a polymer)
• Some of these allotropes can be further divided into different forms based
• on their crystal structure (e.g. -S8 and β-S8 have different densities and
• melting points).
• Naturally occurring sulfur is -S8, eight sulfur
atoms in a puckered ring often called a crown.
This form of sulfur is insoluble in water.
• If sulfur is heated to 400 oC then rapidly cooled
(e.g. by pouring into cold water), we get “plastic sulfur” which can be pulled into
threads.
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The Frasch process• The Frasch process is an extraction
technique.
• In Texas and Louisiana, sulfur deposits of 60-100 meters thick are 400-800• meters underground.
• Superheated water (160oC liquid, 16 bar) melts the sulfur then hotcompressed
• air (20-25 bar) forces the molten sulfur • up a third pipe.
• It takes 10-15 kg of water to extract 1 kg of S8
• The sulfur produced is 98-99.5% pure and can be
• poured into moulds or distributed as a liquid.
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The Claus process– The Claus process generates S8 from H2S.
– Mandated emission limits for H2S in
– the oil and gas industry. Sour gas wells!!
– Two-step process.
1) H2S is burned in the presence of O2.
– (exothermic)– 2) SO2 is reacted with additional H2S.
– (exothermic but requires a catalyst).
– In practice, what is done is to pipe a mixture of H2S and O2
– into a combustion chamber where – most of it reacts to form S8. The
– remaining H2S and SO2 produced
– are then piped into two sequential – reaction chambers where they – complete the second step.
Oxoacids of Sulfur• Oxoacids of sulfur are strong acids.
When SO3 is dissolved in water,
• sulfuric acid is produced:
• - If SO3 is bubbled through concentrated sulfuric acid, one produces
• “fuming sulfuric acid” a.k.a Oleum:
• y SO3.H2O or H2SO4.xSO3
• - Intermediate in production of sulfuric acid. Used in the manufacturing of
• TNT.• - When power plants burn sulfur-
containing coal or oils, they release sulfur
• dioxide which reacts with another pollutant, nitrogen dioxide, to produce
• sulfur trioxide and nitrogen monoxide:
• SO3 produces dissolves in atmospheric water vapour causing acid rain!
Oxoacids of Sulfur• Sulfur oxoanions – Sulfate SO4
-2 and Sulfite SO3
-2.
• - More complicated oxoanions with bridging sulfur
• Ex) S2O4-2 S2O6
-2 S2O8-2 S4O6
-2
• Draw the Lewis structures of sulfur trioxide and sulfite.
How do are these two species similar? How do they differ?
If you dissolved 1 mole of each in a liter of water, which would give you a
Solution with a lower pH?
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