Nature of Arsenic
Classification
Arsenic is classified as a metalloid. This means it possesses characteristics that are intermediate between those of metals and non-metals. For example, it can conduct electricity, but not as efficiently as a typical metal.
Physical Attributes of Arsenic
Allotropic Forms and Appearance
Arsenic can exist in several allotropic forms, meaning it can have different structural arrangements of its atoms, leading to varied physical properties. The most stable and common allotrope is grey arsenic, also referred to as metallic arsenic.
- Color: Grey arsenic exhibits a steel-grey color, which may appear duller or darker grey due to tarnishing when exposed to air. Another allotrope, yellow arsenic, is soft and waxy with a distinct bright yellow color, but it is highly unstable and converts to grey arsenic at room temperature. Black arsenic is also a known, less common allotrope.
- Texture: Grey arsenic is typically brittle and crystalline. Its texture can be described as resembling a metal but without the malleability or ductility of true metals.
- State of Matter: At standard room temperature (approximately 25°C), arsenic is a solid.
Thermal Properties
- Melting Point: Under standard atmospheric pressure, arsenic does not melt but undergoes sublimation. However, under increased pressure (specifically, above 3.86 MPa or 38.1 atmospheres), grey arsenic has a melting point of approximately 817 °C.
- Boiling Point: Under standard atmospheric pressure, arsenic sublimes at approximately 614 °C. This means it transitions directly from a solid state to a gaseous state without first becoming a liquid.