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    24sec4 24sec4 Presentation Transcript

    • 24.4 Hydrogen and Noble Gases
    • Hydrogen
      • Isotopes
      • Three isotopes of hydrogen are known:
      • Percent Alternate
      • Form Abundance Name Symbol
      • 1 H 99.985 Protium
      • 2 H 0.015 Deuterium 3 H trace Tritium
      • Note: Tritium is radioactive with a half-life of 12.3 years. It emits  - .
    • Hydrogen
      • Most abundant element in universe, but on Earth it is generally just found in compounds
      • Found in living things, coal, natural gas, petroleum and petroleum products
      • Found in Group 1A, but is not a metal, it is not a good conductor; it does react w/ halogens though and can have a 1+ charge
      • Also can act like a halogen and react w/alkali metals to for m hydrides ( H - )
    • Physical properties of H 2
      • Hydrogen is a colorless gas with an extremely low melting and boiling point.
      • This indicates that the London forces are very weak.
      • H 2 molecules actually repel each other under ordinary conditions.
      • At 25 o C and 1 atm pressure, the density of H 2 is 0.0824 g/L - the lowest density of any substance under these conditions.
    • Preparation of H 2
      • Industrially, most hydrogen is produced from hydrocarbons and steam - water-gas shift reaction .
      • (1) CH 4 (g) + H 2 O (g) 3H 2 (g) + CO (g)
      • (2) CO (g) + H 2 O (g) H 2 (g) + CO 2 (g)
      • Another way to produce Hydrogen is the Bosch process: steam is passed over red-hot iron
      • 3Fe (s) + 4H 2 O (g) --------Fe 3 O 4(s) + 4H 2(g)
      Catalyst, 900 o C Catalyst 200-400 o C
    • Uses of H 2
      • More hydrogen is used to make ammonia by the Haber process than for any other purpose.
      • Another use is hydrogenation of vegetable oils to make margarine and vegetable shortening.
      Vegetable oil + H 2 Margarine Ni Heat
    • Water
      • Most of the hydrogen on Earth is in the form of water.
      • Water is the only liquid that is common on Earth.
      • Hydrogen bonding by water accounts for many of its unique properties.
        • High melting and boiling point
        • Large temperature range for the liquid form.
        • High specific heat.
    • Noble Gases
      • Group O elements
      • Are very unreactive (inert gases)
      • Flourine will react w/ Xe to form XeF 4, and Kr and Rn have been found to form a compund
      • Occur in atmosphere in rare amounts (rare gases)
      • He is used to fill balloons; Ne and He are mixed w/ oxygen to fo rm an artificial atmosphere ( deep sea divers)
      • Used in neon signs
      • Ar,Kr,Xe used in flashbulbs