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

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• 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?