Arsenic was known as sandarache in 4th century BCE. First clearly recognized as element in 1649 by Johann Schroeder. Found in Earth's crust at about five grams per ton. Mostly occurs in over 150 minerals as sulfides and arsenides
Density is mass per unit volume of a material. SI unit is kilogram per cubic meter (1kg/m³). Density can be calculated using formula: Density = Mass / Volume
Matter is any substance that has mass and occupies space. Matter exists in three basic states: solid, liquid, and gas. Atoms and substances are made up of tiny particles called matter
Matter exists in three states: solids, liquids, and gases. Particle arrangement determines state: solids have strong forces, liquids moderate, gases negligible. New states: plasma (electrons and ions) and Bose-Einstein condensate (atoms in single quantum state)
Solids have definite shape and volume due to tightly packed molecules. They have high density and can be either hard or soft. Solids have specific melting points and can be conductors or insulators
Physical changes are reversible, like melting ice into water. Material remains structurally same before and after change. Examples include texture changes and phase transformations. Physical changes involve only surface texture, not substance composition