Group 15 Elements also known as Nitrogen Group or Nitrogen Family constitute Nitrogen (N), Phosphorus(P), Arsenic(As), Antimony(Sb), Bismuth(Bi) and Moscovium(Mc).
Let us look at the history of the 6 elements in the Nitrogen family.
Nitrogen has been known since the Egyptian Era, in the form of the compound Salammoniac. In the 1760s two scientists, Henry Cavendish and Joseph Priestley conducted an experiment, in which nitrogen was isolated from air, but neither of the two scientists were aware of the result of an undiscovered element. Later, in 1772, Daniel Rutherford realised that the isolated gas was Nitrogen.
Phosphorus was first discovered by Hennig Brandt in 1669. Brandt produced the element by heating the evaporated urine and condensing the resulting phosphorus vapor in water.
Arsenic compounds have been known for at least 5000 years. Elemental arsenic was discovered in the 13th century by Albertus Magnus.
Antimony was discovered much before 5000 years ago.
Bismuth was first discovered in 1400, by an alchemist. It was originally thought to be the same as lead, but in 1753, Claude Francois Geoffroy proved it to be different than lead.
Moscovium was first synthesized in 2003 by Russian and American scientists at the Joint Institute for Nuclear Research (JIINR) in Dubna, Russia.
The Group 15 elements
The elements of this group show certain general similarities in chemical behaviour, though they are chemically differentiated from one another. These similarities reflect common features of the electronic structures of their atoms.
|Atomic Mass (amu)||14.01||30.97||74.92||121.76||209.98|
|Valence Electron Configuration||[He]2s2 2p3||[Ne]3s2 3p3||[Ar]3d10 4s24p3||[Kr]4d105s25p3||[Xe]4f14 5d106s26p3|
Boiling point (°C)
|Density (g/cm3) at 25°C||1.15(g/L)||1.8||5.7||6.68||9.79|
|Atomic Radius (pm)||56||98||114||133||143|
|First Ionization Energy (kJ/mol)||1402||1012||947||834||703|
|Common Oxidation state(s)||-3 to +5||+5, +3, -3||+5, +3||+5, +3||+3|
|Ionic Radius (pm)||146(-3)||212(-3)||58(+3)||76(+3)||103(+3)|
Trends in Group 15 Elements
Below are the trends listed with respect to the group 15 elements:
- Electronic Configuration
- The valence shell configuration of group 15 elements is ns2 np3.
- The s-orbital for each element in this group is completely filled and the p-orbitals are half-filled, which makes their configuration extra stable.
- Atomic and Ionic Radii
- Going vertically down the group, one can find that a new orbital is added to the atom.
- This addition increases both the atomic and the ionic radii of the group.
- However, from Arsenic to Bismuth shows only a small increase in ionic radius, due to the presence of completely filled d and/or f orbitals.
- Ionisation Enthalpy
- It is the amount of energy required to remove an electron from the atom.
- The closer the electron is to the nucleus, the stronger is its hold and thus more is the energy required to remove the electron.
- Going down the group, it can be observed that the radius of the atom increases and thus IE decreases.
- With an increase in atomic size, down the group, electronegativity decreases, due to the increase in distance between the nuclei and the valence shell.
- Physical Properties
- Going down the group, there is a significant increase in the metallic character of the elements, the first element nitrogen being a gas.
- Nitrogen and phosphorus are non-metals, Arsenic and Antimony are metalloids and Bismuth is a metal.
- The boiling point is also observed to increase down the group.
- All the elements, except for nitrogen, have allotropes.
- Chemical Properties
- The valence shells of the p-Block elements have a configuration of ns2 np3.
- Common oxidation states are -3, +3 and +5.
- The tendency to gain three electrons to create a -3 oxidation state, decreases down the group, due to the increase in atomic radii.
- The stability of the +5 state decreases and the +3 state increases, due to the inert pair effect.
- Liquid Nitrogen is a commonly used cryogenic liquid.
- Nitrogen is biologically found in amino acids and DNA. Nitrates occur in some plants, due to bacteria in the nodes of these plants. A typical 70kg human contains 1.5kg of nitrogen.
- Nitrogen in the form of ammonia is a nutrient critical to most plants’ survival. Synthesis of ammonia accounts for about 1–2% of the world’s energy consumption and the majority of reduced nitrogen in food.
- Phosphorus is used in matches and incendiary bombs.
- Phosphorus is found biologically in the form of phosphates in DNA and ATP. It is also found in foods such as fish, liver, turkey, eggs. A typical 70 kg human contains 480 g of phosphorus.
- Phosphate fertilizer helps feed much of the world.
- Arsenic was historically used as a Paris green pigment, but is not used this way anymore due to its extreme toxicity.
- Arsenic in the form of organoarsenic compounds is sometimes used in chicken feed.
- There is 7mg of arsenic present in a 70kg human.
- Antimony is alloyed with lead to produce some bullets.
- There is 2mg of antimony present in a 70kg human.
- Antimony currency was briefly used in the 1930s in parts of China, but this use was discontinued as antimony is both soft and toxic.
- Bismuth subsalicylate is the active ingredient in Pepto-Bismol.
- Humans ingest on average less than 20 μg of bismuth per day. There is less than 500 μg of bismuth in a typical 70 kg human.
The most abundant element in the atmosphere of the nitrogen family is Nitrogen.
As we move down in Group 15, we can see the inert pair effect. This effect impacts the penetration effect of ‘s orbitals. These orbitals penetrate and come closer to the nucleus and enjoy the greater nuclear attraction. Also, these orbitals, then, don’t participate in bonding. So, p electrons can be easily removed but not s electrons.
This is the reason why the stability of the +3 oxidation state increases in heavier elements of Group 15 in comparison with the +5 oxidation state.
More on P Block