Pnictogens

Pnictogens are the elements in group 15 of the periodic table. This group includes nitrogen (N), phosphorus (P), arsenic (As), antimony (Sb), and bismuth (Bi). The group also includes the synthetic superheavy element moscovium (Mc), which does not occur naturally.

What unites these elements is their outer electron configuration: each has five electrons in its outermost shell (configuration ns² np³). This affects how they bond with other elements, and they typically form either three or five bonds.

Name and origin

The term 'pnictogen' derives from the Greek word for 'choking' or 'to choke', alluding to nitrogen's inability to sustain combustion. An alternative common name is the 'nitrogen group', since nitrogen is the lightest element in the group. The International Union of Pure and Applied Chemistry (IUPAC) designates this group as 15.

Variation within the group

Moving down the group, properties transition from nonmetallic to metallic. Nitrogen and phosphorus are nonmetals; arsenic and antimony are classified as metalloids (semimetals); bismuth is distinctly metallic. Atomic radius and atomic mass increase down the group, while electronegativity decreases.

Common compounds

Nitrogen occurs naturally chiefly as diatomic nitrogen gas (N₂), comprising more than three-fourths of Earth's atmosphere. It forms ammonia (NH₃) and nitric acid. Phosphorus is found in phosphate minerals and is used in agriculture and industry. Arsenic and antimony are used in electronic devices and metal alloys. Bismuth is used in stomach medicines and in low-melting alloys.

Importance to life

Nitrogen and phosphorus are essential to living organisms: nitrogen is a component of amino acids and nucleic acids, while phosphorus is present in DNA, RNA, and ATP, which carries energy in cells. Arsenic and some of its compounds are toxic above certain threshold levels, and naturally occurring arsenic has been detected in groundwater in some parts of the world at concentrations affecting health.