Arsenic Arsenic Arsenic is a chemical element with symbol As and atomic number 33. Arsenic occurs in many minerals, usually in combination with sulfur and metals, but also as a pure elemental crystal. Arsenic is a metalloid. It has various allotropes, but only the gray form, which has a metallic appearance, is important to industry. The primary use of arsenic is in alloys of lead (for example, in car batteries and ammunition). Arsenic is a common n-type dopant in semiconductor electronic devices, and the optoelectronic compound gallium arsenide is the second most commonly used semiconductor after doped silicon. Arsenic and its
Tellurium alpha decay. The atomic mass of tellurium (127.60 g·mol) exceeds that of iodine (126.90 g·mol), the next element in the periodic table. With an abundance in the Earth's crust comparable to that of platinum (about 1 µg/kg), tellurium is one of the rarest stable solid elements. In comparison, even the rarest of the stable lanthanides have crustal abundances of 500 µg/kg (see Abundance of the chemical elements). This rarity of tellurium in the Earth's crust is not a reflection of its cosmic abundance. Tellurium is more abundant than rubidium in the cosmos, though rubidium is 10,000 times more abundant in