Melting points group 2 metal oxides

In general, for all the studied oxides there is no uniform dependence of the oxide solubility products in the given melt and the melting point of the oxide. This seems to be connected with different crystalline structures of the said oxides, and with different degrees of covalence of the oxides formed by metals belonging to the s- and d-element groups. 

Platinum is classed by tradition and commercial usefulness as a precious metal that is soft, dense, dull, and silvery-white in color, and it is both malleable and ductile and can be formed into many shapes. Platinum is considered part of the precious metals group that includes gold, silver, iridium, and palladium. It is noncorrosive at room temperature and is not soluble in any acid except aqua regia. It does not oxidize in air, which is the reason that it is found in its elemental metallic form in nature. Its melting point is 1,772°C, its boiling point is 3,827°C, and its density is 195.09g/cm. ... 

The melting points, boiling points, and heats of vaporization for the zinc group members are lower than for any other group of metals except la. By the argument presented on page 99, one would expect these metals to have abnormally high" oxidation potentials that is, they should be less noble than other metals with comparable ionization potentials. Thus zinc (ionization potential 9.39 volts) is more easily oxidized than iron (ionization potential 7.90 olts), cadmium (ionization potential 8.9S volts) is more easily oxidized than nickel (ionization potential 7.63 volts), and mercury (ionization potential 10.43 volts) more easily than platinum (ionization potential 8.88 volts). Note that the ionization potentials would favor the opposite order in each case. 

Chromium has an atomic number of 24, an atomic weight of 51.996 consisting of four stable isotopes ( Cr = 84%), and a density of 7.14 gcm (Adriano, 1986). Crystalline Cr is steel-gray in color, lustrous, hard metal that has a melting point of 1,900 °C and a boiling point of 2,642 °C. It belongs to group VIb of the transition metals and in aqueous solution Cr exists primarily in the trivalent (4-3) and hexavalent (+6) oxidation states. Chromium, as well as Zn, are the most abundant of the heavy metals with a concentration of about 69p,gg in the hthosphere (Li, 2000). 

---