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**Symbol:** As **Atomic number:** 33 **International name:** Arsenic **Relative Atomic Weight:** 74.9216 **Description:** Arsenic exists in several allotropic forms, the most common being gray arsenic. Gray arsenic is a crystalline, brittle material with a glossy, semi-gray appearance. Its compound, arsenic oxide (commonly referred to just as arsenic), is a potent poison and historically believed to have contributed to the death of French Emperor Napoleon Bonaparte. **Applications:** Gallium arsenide (GaAs), an arsenide compound, is widely used in the production of semiconductors found in the processors of modern computers. **Occurrence:** Arsenic is a relatively rare element on Earth. It is found in minerals such as arsenopyrite (FeAsS). **Structure:** Arsenic has a layered structure and crystallizes into trigonal (rhombohedral) crystals.