Microsoft Word - WaterChemistry

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Metalloids

Element Allotropes

Boron:

 Amorphous boron - brown powder - B 12 regular icosahedra

 α-rhombohedral boron

 β-rhombohedral boron

 γ-orthorhombic boron

 α-tetragonal boron

 β-tetragonal boron

 High-pressure superconducting phase

Silicon:

 Amorphous silicon

 crystalline silicon, Diamond cubic structure

Arsenic:

 Yellow arsenic - molecular non-metallic As 4 , with the same

structure of white phosphorus

 Gray arsenic, polymeric As (metalloid)

 Black arsenic - molecular and non-metallic, with the same structure

of red phosphorus

Germanium: ^ α-germanium – semi-metallic, with the same structure of diamond^

 β-germanium - metallic, with the same structure of beta-tin

Antimony:

 blue-white antimony - the stable form (metalloid)

 yellow antimony (non-metallic)

 black antimony (non-metallic)

 explosive antimony

Polonium: ^ α-polonium - simple cubic (metallic) β-polonium - rhombohedral (metallic)

Metals
Among the metallic elements that occur in nature in significant quantities (up to U,
without Tc and Pm), 27 are allotropic at ambient pressure: Li, Be, Na, Ca, Ti, Mn, Fe,
Co, Sr, Y, Zr, Sn, La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Yb, Hf, Tl, Th, Pa and U. Some phase
transitions between allotropic forms of technologically-relevant metals are those of Ti at
882 ̊C, Fe at 912 ̊C and 1394 ̊C, Co at 422 ̊C, Zr at 863 ̊C, Sn at 13 ̊C and U at 668 ̊C
and 776 ̊C.