ZINC


Physical Properties

Atomic Number: 30
Mass Number: 65.39
Electron Configuration: 1s²2s²2p⁶3s²3p⁶4s²3d¹⁰
Crystal Structure: Hexagonal Close-Packed
Density: 7.14 g/cm³
Melting Point: 420^oC
Boiling Point: 907^oC
Atomic Radius: 133 pm
Ionic Radius: 74 pm (Zn²⁺)
Important Oxidation States: +2
Standard Reduction Potential: -0.76 volts for Zn²⁺(aq) + 2e^- = Zn(s)

Zinc is the last member of the first transition series. In many ways, the properties of zinc more closely resemeble those of the alkaline earth metals than the transition metals. Whereas most transition metals form a variety of oxidation states, zinc only forms the +2, which corresponds to the removal of the two 4s electrons. Whereas most of the transition metal compounds are colored, all zinc compounds are white. The reason for this lies with the fact that the 3d orbitals are completely filled. The transfer of electrons from lower energy orbitals to higher energy orbitals, the mechanism responsible for the color of most transition metal ions, cannot take place with zinc.

As a metal zinc is hard and lustrous. It is obtained primarily from sulfide ores such as sphalertie. Zinc has a density comparable to chromium and is less dense than iron, nickel, or cobalt. Zinc is widely used as an anode in batteries. Galvanized iron and steel objects containing a coating zinc, which protects them from oxidation.

Zinc metal is fairly reactive and is readily ozidized. Zinc will readily react with hydrochloric acid, a reaction commonly used to generate hydrogen in the labortory. Zinc will replace other metals from solution. When a zinc strip is placed in a solution of copper chloride, the blue color of the solution slowly fades as zinc replaces the copper in solution, and a precipitate of reddish copper metal is formed.

Zinc forms many compounds, including the fluoride, chloride, bromide, iodide, carbonate, oxide, and sulfide. Zinc sulfide occurs naturally in two forms, sphalertie and wurtzite. Both are structural prototypes. Sphalertie (also known as zinc blende) is the more common of the two and consists of a cubic close-packed array of zinc ions with the sulfde ions filling half of the tetrahedral holes. In the sphalertie structure, thge zinc ions form a hexgonal close-packed array with the sulfide ions filling half of the tetrahedral holes.

The Reactivity of Zinc In this photo, a zinc strip has been dipped in a beaker containing copper(II) chloride. A fairly vigorous reaction has occurred in which the copper(II) ion is reduced to copper metal, which coats the zinc strip.