Ahad, 16 November 2008


The Periodic Number Of Element
#The number of shells occupied with electros in its atom

Group 18 Element

# insoluble in water # low density

# cannot conduct electricity # colourless & unreactive

# poor conductor of heat # exist in monoatomic gases

Uses Of Group 18 Elements
  • Helium # to cool the coils in body scanners in medical field
  • Neon # advertising light on billboard and television tubes
  • Argon # used in filament bulb & provide an inert atmosphere for welding at high temperature.
  • Krypton # used in laser to repair retina & to fill photographic flash lamps.
  • Radon # used to treat cancer patients
  • Xenon # used in bubble chamber in atomic and making rlrctrin tubes and stroboscopic


Going Down Group 1

  • atomic radius increase
  • density increase
  • melting and boiling points decrease


Physical properties

  • poor conductor of heat # poor electric conductor
  • low melting & boiling points # called as halogen (salt former).
  1. Fluorine # pale yellow gas
  2. Chlorine # greenish-yellow gas
  3. Bromine # reddish-brown liquid
  4. Iodine # purplish-black solid

Going Down Group 17

  • increase in size # higher density
  • less reactive # increase the atomic radius
  • Increase melting & boiling points # decrease the force of attraction

Elements In A Period

Across Period 3

  • the proton number increasesby one unit from one element to the next element,
  • all atoms of the elements have three shells occupied xith electron.
  • the number of valemce electrons each atom increases from 1 to 8.
  • all the elements exist as solid except chlorine and argon which are gases.
  • the atomic radius of elementsdecreases.
  • the electronegativity of element decrease.

Uses Of Semi-metal In Industries

  • Silicon and germanium are used in semiconductors

- enable to surf internet and watch television.

  • Semiconductors are used to make diods and transistors.


  • Transition elements show different oxidation numbers in their compounds.
  • Transition elements form coloured ions or compounds.
  • Their compounds are useful catalysts.

Uses In Industries

  • Iron is used as a catalysts in the manufacture of ammonia in Haber Process.
  • Platinum is used as a catalyst in the Ostwald a process of manufacturing of nitric acid.
  • Nickel is used as a catalyst in the manufacture of margerine.
  • Vanadium(V) oxide is used as a catalyst in the Contact Process for the manufacturing of sulphuric acid.

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