Arsenic belongs to group 15, which is called the nitrogen family. This family of elements also includes nitrogen, phosphorus, antimony and bismuth. All elements in this family have the same electron configuration in their outermost shell (ns2np3).
Arsenic is a metalloid element that is poisonous. At room temperature, it is a yellow or gray solid. Its toxicity makes it useful in weed killers and insecticides. Arsenic's properties fall within the mid-range of its family. Its atomic number is 33, and the atomic mass is 74.92. This makes it more massive than calcium and phosphorus but less massive than antimony and bismuth. Like all elements in this family, arsenic's common oxidation state is -3.