The Air/ The Atmosphere

• Major Points--
  • what's in air
  • what's its role --- good, bad, both?
  • where does it come from
  • what should we do?
• Chemistry Basics (as we go-- in context)
  • Elements and Chemical Compounds
  • Symbols and Formulas
  • Naming simple compounds
  • Atoms, Molecules and Chemical Bonds
  • Gases: The model of a gas
  • Chemical reactions
    • writing chemical equations

• mostly nitrogen, oxygen (99%)
• some carbon dioxide, water vapor, argon
• Some less pleasant species
  • natural sources and man made
    • carbon monoxide
    • sulfur dioxide
    • nitrogen oxides
    • hydrocarbons
    • formaldehyde
    • ozone

• global / national / local
• air pollution, smog, respiratory illnesses
• global warming and green house effect
• ozone loss (yes, ozone is toxic but good for you)

• most industrial activity leads to air pollution
• our s fuel choice, transportation tied to air quality
• often long range problem--can it be faced now?

• reduce CO from cars -- get water pollution
• reduce hydrocarbon, increase nitrogen oxides
• nuclear waste vs. greenhouse gases

• room ventilation/ housing design
  • carbon dioxide
  • humidity levels
  • radon
  • carbon monoxide levels
  • interior air (soaps, cleaners, glues, paints, ...)

• mostly nitrogen and oxygen
  • N = symbol for the element Nitrogen
  • exists as a diatomic molecule,
    • N₂ is more descriptive
  • O = symbol for the element
    • also a diatomic molecule, O₂
  • next species is Argon
  • Ar = symbol for element
  • Ar exists as isolated atoms (no subscript = 1)

• name suggests two elements
  • Carbon (C)
  • Oxygen (O) ---> oxide
• di = 2
• CO₂
• exists as a molecule-- two oxygen
  • chemical bonds link to a carbon
• actually O - C - O straight line
  • (but name doesn't tell you that)

• chemically water is H₂O
• hydrogen dioxide
  • but universally known as water
• we are used to liquid water
  • exists as ice (solid)
  • exists as steam or vapor (gas)

• most materials (elements and compounds)
• exist in several forms or phases
• temperature usually determines which
• Nitrogen-- room temperature, a gas
  • very cold-- forms a liquid
  • (pours, boils -178 ^oC below zero)
  • on a floor or desk top, like water on red hot steel
  • cold enough to condense Ar , O₂ and CO₂
    • mostly you see frost, H₂O
  • liquid is about 1000 times as dense as gas
    • one liter (about a quart)
    • weighs about 1 kg (2 lb.)
    • similar to water, but colder

• one liter of nitrogen (or air)
  • weighs about 1 gram
  • 1/1000 kg

• density = mass/volume

• Cold Carbon Dioxide-- Solid called Dry Ice
  • -78^oC
  • turns into a gas without melting
    • (sublimation)

• homogeneous (uniform)
• well, almost
• varies (called the weather)
• small changes over 10's - 100's of miles
  • pressure changes (concentration)
  • humidity varies (composition)
• pressure and % changes with altitude
• downwind of a fire
  • less O₂, more H₂O and CO₂
• city vs. country
  • combustion products, air pollution
• following a storm
  • lightning makes NO and NO₂
• still, remarkably uniform

• relatively little chemical activity in air
• (more if you are bacteria, soybeans, termites)

• critical to life as we know it
• key to fires, rust, metabolism

• varies a lot, so we generally list dry air %
• leads to rain, fog; few reactions

• Inert gas, virtually no reactions
• (Used in welding, light bulbs because it is inert)

• plants take it in during Photosynthesis
  • cycle: CO₂ ---sun--> sugars and O₂
  • sugar + O₂ ---in people--> CO₂
  • wood/coal/ oil + O₂ --> CO₂ , energy
  • people get life / energy from the sun

• with little ventilation, CO₂ concentration grows
  • at 0.5% people get quite sleepy
  • cease to function long before no oxygen
  • later-- CO₂ is important Greenhouse gas

• 1 atm (easy)
• 1013 millibars (metric)
  • 101.3 kiloPascals on Canadian Weather)
  • about 30 inches of mercury
  • 760 torr (mm of mercury)
  • 14.7 ponds per square inch

• weather-- pressure changes by about 2-5%
• big changes = storms and winds
• usually tiny changes

....end of notes, 8/29/01

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