Thursday, October 21, 2010
Periodic Properties
Atomic radius: 135 pm
1st ionization energy: 906.4 kJ mol-1 2nd ionization energy: 1733.2 kJ mol-1
3rd ionization energy: 3832.6 kJ mol-1
Electron affinity: kJ mol-1
Electronegativity Value in Pauling units
Pauling electronegativity 1.65
Sanderson electronegativity 2.23
Allred Rochow electronegativity 1.66
Mullikan-Jaffe electronegativity 1.65 (sp orbital)
Subatomic Particles
Zn-62
Zn-63
Zn-64
Zn-65
Zn-66
Zn-67
Zn-68
Zn-69m
Zn-70
Zn-72
Chemical Properties of Zinc
Chemical Properties
Zinc dissolves in both acids and alkalis. An alkali is a chemical with properties opposite those of an acid. Sodium hydroxide ("common lye") and limewater are examples of alkalis. Zinc does not react with oxygen in dry air. In moist air, however, it reacts to form zinc carbonate. The zinc carbonate forms a thin white crust on the surface, which prevents further reaction. Zinc burns in air with a bluish flame.
Reactions of Zinc: with air, water, halogens, acids, and bases
Highly flammable
Physical Properties
Zinc is a bluish-white metal. It is brittle at surrounding temperatures but is malleable at 100 to 150°C. It is a good conductor of electricity, and burns in air at high red heat that then evolves into white clouds of the oxide.
Density 7.11 g.cm-3 at 20°C
Melting point 420 °C
Boiling point 907 °C
History and Discovery of Zinc!
Centuries before zinc was recognized as a distinct element, zinc ores were used for making brass (a mixture of copper and zinc). A brass dating from between 1400-1000 BC has been found in Palestine. An alloy containing 87% zinc was found in prehistoric ruins in Romania. Zinc ores with copper was apparently discovered in Cyprus and was used later by the Romans. The metal was rediscovered later in Europe. William Champion set up a zinc industry in Bristol (England) in the 1740s. The symbol was written by many chemist.