Polonium electrical resistivity

In the vapor phase, arsenic, like phosphorus, exists as tetrahedral AS4. Antimony and bis-mnth also have similar a forms. These three elements have a somewhat metallic appearance bnt are only moderately good conductors. Arsenic is the best conductor in this group but has an electrical resistivity nearly 20 times as great as copper. Bismuth is the heaviest element to have a nonradioactive nucleus polonium and all heavier elements are radioactive. 

Basic physical properties of sulfur, selenium, and tellurium are indicated in Table 1.3. Downward the sulfur sub-group, the metallic character increases from sulfur to polonium, so that whereas there exist various non-metallic allotropic states of elementary sulfur, only one allotropic form of selenium is (semi)metallic, and the (semi)metallic form of tellurium is the most common for this element. Polonium is a typical metal. Physically, this trend is reflected in the electrical properties of the elements oxygen and sulfur are insulators, selenium and tellurium behave as semiconductors, and polonium is a typical metallic conductor. The temperature coefficient of resistivity for S, Se, and Te is negative, which is usually considered... 

The trend towards greater metallic character in the elements is complete at polonium. Whereas sulfur is a true insulator (specific resistivity in fiQ-cm = 2 x 1023), selenium (2X1011) and tellurium (2 x10s) are intermediate in their electrical conductivities, and the temperature coefficient of resistivity in all three cases is negative, which is usually considered characteristic of non-metals. Polonium in each of its two allotropes has a resistivity typical of true metals ( 43 juQ-cm) and a positive temperature coefficient. The low-temperature allotrope, which is stable up to about 100°, has a cubic structure, and the high temperature form is rhombohedral. In both forms the coordination number is six. 

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