1) PLATINUM (Pt): CHEMICAL-PHYSICAL PROPERTIES
- Atomic number: 78
- Atomic weight: 195.09
- Electronic configuration: [Xe] 4f14 5d10
- Atomic radius (nm): 0.130
- 1st ionization potential (eV): 9.0
- Electrode standard potential (V): 1.20
- Density (g/cc): 21.45
- Melting T (C): 1772
- Boiling T (C): 3827
- Oxidation Numbers (ON): +2, +4

2) PRESENCE IN NATURE AND PRODUCTION
Pt is one of the noble metals for its very high resistance to corrosion, brightness and rarity.
It was discovered in 1735 by A. De Ulloa and its name derives from the Spanish diminutive of "plata" (silver) that is very similar metal, in its appearance.

In reality, Pt is less hard than Ag and equally very malleable and, consequently, easy to be worked in very subtle wires and sheets.

It's very rare in the earth crust, with an esteemed presence of 5*10^(-7) %.
It can be found at the elementary state dispersed in some alluvional deposits that have been already exploited, in the largest part; then, in volcanic rocks and, this time combined, in few rare ores like the SPERILLITE (PtAs2), from which more than half of Pt is extracted in the world.
Then, it's also present in metallic meteorites (about 0.003%).

In nature, Pt is always impure for the presence of other noble metals, like Au, Pd, Ir and other less noble, like Fe, Ni, Cu; the last are separated dissolving them easily with H2SO4 but, to purify Pt from the other noble metals is a hard work, with long and complex chemical processes.
At the end, Pt is obtained as (NH4)2PtCl6 (AMMONIUM HEXACHLOROPLATINATE) that, heated in absence of water, gives a residual of spongeous Pt, that can be melt and transformed in bars.

3) CHEMICAL PROPERTIES AND COMPOUNDS
- Pt has two main ON, +2 and +4 and it forms a great number of complex salts: for ex., if we dissolve the simple salt PtCl2 or PtCl4 in HCl solution, we obtain, respectively, H2PtCl4 (TETRACHLOROPLATINIC ACID) and H2PtCl6 (HEXACHLOROPLATINIC ACID), yellow-orange.
Also CN- (cyanides) form stable complexes with Pt in solution:
[Pt(CN)4]- and [Pt(CN)]- .

- Pt (II) complexes are tetra-coordinated dsp2, with a plane and square shape, while those of Pt (IV) are hexa-coordinated (d2sp3), with an octaedral shape, formed by two pyramids with a square base in common and the Pt atom in its centre.

- Pt is very difficult to dissolve and only hot aqua regia (3 parts of HCl and 1 part of HNO3) can attack it successfully, forming H2PtCl6.

3Pt + 18HCl + 4HNO3 -> 3H2PtCl6

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