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Elements on Planet Earth

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					Elements on Planet Earth


   In the Air , In the Crust,
         In the Water.
               Background
• Our understanding of the elements has
  progressed from the Fire, Air, Earth, Water
  stage to the current theory that everything is
  composed of atoms.
  Elements In the Atmosphere
• In the atmosphere there are a number of
  elements.
• These are
  –   Nitrogen   78.03 %
  –   Oxygen     20.99 %
  –   Argon      0.94 %
  –   CO2        0.04 %

  Surprised?
  Elements In the Atmosphere
• Oxygen is so reactive it cannot exist for
  more than a moment as an uncombined
  atom. It combines to form O2
• This is called a diatomic molecule
• Nitrogen is essential to all life. It is also a
  diatomic molecule.
• Let’s look at Nitrogen…
  Nitrogen In the Atmosphere
• Nitrogen is an element
• It’s symbol is N
• The smallest particle of nitrogen is the
  nitrogen atom - N
• Nitrogen exists in the atmosphere as a diatomic
  molecule - N2

• There are other elements in the atmosphere
  – H2O , H2S
     CO2 In the Atmosphere
• In the 17th century people began to burn coal
  to heat houses and provide energy for
  commercial use.
• In the 19th century we began to burn
  petroleum fro cars and industry.
• The result has been an increase in the amount
  of CO2 in the atmosphere.
• Increased CO2 is predicted to cause global
  warming.
  – How will warming affect the earth?
          The Hydrosphere
• Many elements are locked in compounds.
• One of the most important compounds is
  H20.
• Water is essential for life and is a solvent
  for many other substances.
• Most compounds are soluble in water.
• All of the water in the hydrosphere contains
  dissolved compounds.
          The Hydrosphere
• Animals living in water depend on
  dissolved O2 to breathe
• Plants that live in water depend on
  dissolved CO2 to breathe
• Sea water contains NaCl , KCl and CaCl2
• These compounds come from rocks and soil
  that have been washed into solution by rain.
               The Crust
• There are many elements in the Earth’s
  crust
• Some - Au, Ag, C - are found as elements.
  Others are found combined as compounds.
• Elements that are stable can be found as
  atoms of pure substance.
• Atoms that are very reactive are found as
  parts of compounds.
        Cycling The Elements
• Elements and compounds cycle through the
  atmosphere, hydrosphere and crust.
• This prevents a buildup of elements in a particular
  part of the Earth.
• Life on Earth needs this cycling
   – CO2 to O2 + C
   – Nitrogen
• Photosynthesis and respiration make use of the
  elements hydrogen, oxygen and carbon, cycling
  them through the atmosphere.
 Photosynthesis and Respiration
• Respiration: what animals do
   Glucose + oxygen --> carbon dioxide + water + energy
   Or
   C6H1206 + 6 O2 -----------> 6 CO + 6 H2O + ENERGY

• Photosynthesis: what plants do
   Sunlight + carbon dioxide + water --> glucose + oxygen
   Or
   6 CO + 6 H2O + ENERGY -----> C6H1206 + 6 O2
Metals
                   Metals
• All elements can be classified as metals ,
  non-metals or metalloids.
• Metals comprise the majority of the
  elements.
• Metals have a characteristic set of
  properties.
                        Metals
• Metals …
  –   can be moulded into shapes (malleable)
  –   can be formed into thin wires (ductile)
  –   conductors or heat and electricity (conductivity)
  –   have characteristic lustre or sheen
  –   High melting and boiling point (except mercury)
                    Non-metals
• Non-metals …
  –   Are usually brittle.
  –   Are poor conductors of heat and electricity.
  –   Have a dull surface (solids)
  –   Have lower melting and boiling points - often gaseous
      at room temperature.
                       Metalloids
• Metalloids have some metal and some non-metal
  properties. They are usually
  –   Solid at room temperature with high boiling temps
  –   Good thermal insulators
  –   Brittle and non-ductile
  –   May or may not be good conductors of electricity.
          In the Periodic Table
• Metals are found on the left side of the table with
  the most active metal in the lower left corner.
• Nonmetals are found on the right side with the
  most active nonmetal in the upper right hand
  corner of the chart.
• Since the most active metals react with water to
  form bases, the Group I metals are called alkali
  metals.
• Elements found along the dark line in the periodic
  table are called metalloids. They are the elements
  which have certain characteristics of metals and
  other characteristics of nonmetals.
• Some examples of metalloids are boron, silicon,
  arsenic, and tellurium.

				
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