Group 15: the nitrogen group (pnictogens)
Group 15 contains nitrogen, phosphorus, arsenic, antimony, bismuth and the synthetic element moscovium. Every atom has five outer electrons, three of them unpaired, so the lighter members typically form three bonds, as in ammonia (NH₃). Like group 14, the column runs from nonmetals at the top to a metal at the bottom.
Position in the periodic table
Elements in this group
Five outer electrons: ns² np³
Each configuration ends in ns² np³, from nitrogen ([He] 2s² 2p³) to bismuth ([Xe] 4f¹⁴ 5d¹⁰ 6s² 6p³). Three electrons short of an octet, these atoms can gain three to form ions such as the nitride ion N³⁻, or share three in covalent bonds, as in ammonia and phosphine (PH₃).
They also show the positive oxidation states +3 and +5. Nitrogen covers the widest range, from −3 in ammonia to +5 in nitric acid (HNO₃), while bismuth, at the bottom, is mainly +3.
From gas to metal
Nitrogen is a gas of N₂ molecules that melts at 63.15 K, while white phosphorus is a waxy solid that melts at 317.3 K. Arsenic and antimony are gray metalloids, and bismuth is a brittle metal. Electronegativity drops from 3.04 for nitrogen to 2.19 for phosphorus and 2.02 for bismuth, and first ionization energy falls by half, from 14.534 eV to 7.289 eV. Density climbs from 1.823 g/cm³ for phosphorus to 9.78 g/cm³ for bismuth.
Where you meet group 15
Nitrogen makes up about 78% of the air, and nitrogen and phosphorus are the N and P on fertilizer bags. Phosphorus links the units of DNA and stores energy in ATP, and red phosphorus is in the striking strip of a matchbox. Arsenic compounds are notorious poisons, yet gallium arsenide is used in fast electronics. Antimony helps plastics resist fire, and bismuth turns up in pink stomach remedies and fire sprinkler alloys.
Names and a slow surprise
The name pnictogen comes from a Greek word meaning to choke, because pure nitrogen gas suffocates. Bismuth was long thought to be the heaviest stable element, but in 2003 scientists found that bismuth-209 is very slightly radioactive, with a half-life more than a billion times the age of the universe. Moscovium (115) has been made only a few atoms at a time, so its properties are predicted, not measured.
Group 15: properties down the group
Click a column heading to sort.
| 7 | Nitrogen | N | 5 | −3 | 3.04 | 155 | 63.15 K (-210 °C) | 1.251 g/L |
| 15 | Phosphorus | P | 5 | −3 | 2.19 | 180 | 317.3 K (44.2 °C) | 1.823 g/cm³ |
| 33 | Arsenic | As | 5 | −3 | 2.18 | 185 | 1,090 K (816.8 °C) | 5.727 g/cm³ |
| 51 | Antimony | Sb | 5 | −3 | 2.05 | 206 | 903.78 K (630.6 °C) | 6.697 g/cm³ |
| 83 | Bismuth | Bi | 5 | +3, +5 | 2.02 | 207 | 544.7 K (271.6 °C) | 9.78 g/cm³ |
| 115 | Moscovium | Mc | 5 | — | — | — | — | — |