Group 15 of the periodic table
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Group 15 of the periodic table consists of five chemical elements: nitrogen (N), phosphorus (P), arsenic (As), antimony (Sb), and bismuth (Bi). They are also known as pnictogens. The elements of this group share five electrons in the outer shell of the atom (valence electrons), which determines how they bond with other elements.
As one moves down the group, properties shift from nonmetallic to metallic. Nitrogen and phosphorus are nonmetals; arsenic and antimony are classified as metalloids; bismuth is a metal. This transformation is a typical example of how properties change within a group of the periodic table.
Electronic structure
Each element in this group has an electron configuration ending in ns²np³. The three electrons in the p-orbital allow the atom to form three bonds, as in ammonia (NH₃) and phosphine (PH₃). Common oxidation states include −3, +3, and +5, though they vary among the elements.
Nitrogen and phosphorus
Nitrogen exists in Earth's atmosphere in diatomic molecular form (N₂) and constitutes the largest portion of the air. The triple bond in N₂ is very strong, which is why nitrogen is quite stable under normal conditions. Phosphorus does not occur naturally in free form but is found in phosphate minerals. Both elements are fundamental to life: nitrogen is present in proteins and amino acids, while phosphorus is found in DNA, ATP, and bone.
Arsenic, antimony, and bismuth
Arsenic and some of its compounds are toxic; certain groundwaters contain naturally occurring arsenic, which is a public health concern. Antimony is used in metal alloys and in materials that resist fire. Bismuth is a brittle metal with a low melting point and is used in medications for digestive upset and as a lead substitute.
Industrial applications
The Haber–Bosch process converts atmospheric nitrogen and hydrogen into ammonia, which is essential for agricultural fertilizers. Phosphate mined from ore is converted into phosphate fertilizers and phosphoric acid. Some compounds of this group, such as gallium arsenide and indium antimonide, are important in semiconductor technology.