Occurrence of Group 15 Elements: Melting and Boiling Points, Electronegativity

Occurrence of Group 15 Elements: Overview

The lightest component of group \(15,\) like group \(14,\) is nitrogen, which is found in nature as a element. Because they can be easily extracted from their ores, the heaviest elements have been well known for ages.

Molecular nitrogen makes up \(78-80\%\) of the atmosphere’s volume. It is found as sodium nitrate (also known as Chile saltpetre) and potassium nitrate in the earth’s crust (Indian saltpetre). Plants and animals both contain it in the form of proteins. Phosphorus is mostly obtained from phosphate rock and remains of fossil life forms. The mineral phosphorus is the \(11\)th most prevalent in the earth’s crust. Apatites contain phosphorus which is extracted using sand and coal.

At \({\rm{150}}{{\rm{0}}^{\rm{o}}}{\rm{C}}:\)
\({\rm{C}}{{\rm{a}}_3}{\left( {{\rm{P}}{{\rm{O}}_4}} \right)_2} + 6{\rm{Si}}{{\rm{O}}_2} + 10{\rm{C}} \to 6{\rm{CaSi}}{{\rm{O}}_3} + 10{\rm{CO}} + {{\rm{P}}_4}\)

Unfortunately, elemental phosphorus is exceedingly poisonous and volatile. It is absorbed by the calcium in the teeth, and it also destroys the jawbone. This causes a painful condition known as “phossy jaw,” which has been recognised as an occupational hazard of working in the match industry for many years. When \({\rm{P}}\) is heated under high pressure, it forms black phosphorus, which is the most stable form. Bone marrow, milk, and eggs all contain phosphoproteins. Other phosphates are present in fertilisers.

In the earth’s crust, arsenic, antimony, and bismuth are mostly found as sulphide minerals. Arsenic is removed on a large scale by suitable heating minerals in the absence of air. Realgar \(\left( {{\rm{A}}{{\rm{S}}_4}{{\rm{S}}_4}} \right),\) Orpiment \(\left( {{\rm{A}}{{\rm{S}}_2}{{\rm{S}}_3}} \right),\) Arsenolite \(\left( {{\rm{A}}{{\rm{S}}_2}{{\rm{O}}_3}} \right),\) arsenopyrite \(\left( {{\rm{FeAsS}}} \right),\) etc., are among these minerals \(\left( {{\rm{FeA}}{{\rm{s}}_2}} \right).\)

Bismuth is found as bismite \(\left( {{\rm{B}}{{\rm{i}}_2}{{\rm{O}}_3}} \right),\) bismuthinite \(\left( {{\rm{B}}{{\rm{i}}_2}{{\rm{S}}_3}} \right),\) and bismutite \(\left[ {{{\left( {{\rm{BiO}}} \right)}_2}{\rm{C}}{{\rm{O}}_3}} \right]\) minerals. It is, however, mostly produced as a byproduct of copper, lead, tin, silver, gold, and zinc processing plants. The third phase required utilising charcoal to reduce the oxides of bismuth and other metals in heat. This is why chemists have been perplexed by its existence for ages. Because of its somewhat pinkish white sheen, they confused it for other elements.

Because it is one of the few elements whose solid state is less dense than the liquid, bismuth is commonly employed in printing.

Trends of Some Atomic Properties

Atomic Radii

The ionic and atomic radii increase as you move down the group due to the expansion of another main energy level in each advancing element.

Ionisation Enthalpy

When compared to group \(14\) elements, these elements have higher ionisation enthalpy values. Their larger atomic charge, lower nuclear radii, and stable half-filled electronic setups account for this. The ionisation enthalpy values decrease as we travel down the group. This is due to the increasing size of the nuclear nucleus.

Electronegativity

The tendency of a particle to pull a shared pair of electrons closer to itself is known as electronegativity. Because of the rise in atomic radius as one moves down the group, the electronegativity decreases gradually.

Physical Properties

The physical state, boiling and melting points, metallic character, allotropy, and density are all examples of physical qualities. The rest of the elements are solids in nature, except for nitrogen, which is a diatomic gas. Metallic character increases as you move down the group, while the ionisation enthalpy of the elements decreases as their nuclear size grows. 

Trends in Melting and Boiling Points

Because of the continual increase in nuclear size, the melting point increases from nitrogen to arsenic. Because of its distinct diatomic particles, nitrogen has a low melting point. The high melting point of arsenic, on the other hand, is attributed to its goliath layered structure, in which the layers are strongly pushed together.

Despite the fact that the size of the nuclear nuclei increases from arsenic to antimony, their melting points decrease. Antimony, despite having a layered structure, has a lower melting point than arsenic due to the general pressing of particles. Furthermore, owing to the loose packing of atoms caused by metallic holding, bismuth has a lower melting point than antimony. The boiling point, on the other hand, gradually increases from nitrogen to bismuth.
From nitrogen to bismuth, the density of these elements increases.

Allotropy

Except for bismuth, all of the group fifteen elements show allotropy. The two allotropic structures of nitrogen are alpha nitrogen and beta nitrogen. Phosphorus can be found in a variety of allotropic forms. Red phosphorus and white phosphorus are the two most important allotropic structures.
Arsenic can be found in three allotropic forms: black, grey, and yellow. Antimony also possesses three important allotropic forms, namely yellow, metallic, and explosive.

Oxidation States

In the outermost circle of each element in group \(15,\) there are \(5\) electrons. They just need three electrons to complete their octet configuration. The octet can be formed by either picking up three electrons or sharing three electrons using a covalent bonding mechanism. As a result, these elements’ basic negative oxidation state is \(- 3.\) The likelihood of displaying a \(- 3\) oxidation state decreases as one moves along the group. This is due to the expansion of the nuclear size and the metallic character of the nucleus.

By forming covalent bonds, Group \(15\) elements also show positive oxidation states of \(+3\) and \(+5.\) Because of the inert pair effect, the stability of the \(+5\)-oxidation state decreases as one moves down the group, while the stability of the \(+3\) oxidation state increases. In its valence shell, nitrogen has only \({\rm{s}}\)- and \({\rm{p}}\)-orbitals but no d-orbitals. As a result, nitrogen has a covalency of \(4\) at its most extreme. The sharing of its lone pair of electrons with another ion or particle results in a covalency of four.

Phosphorus and the other elements have a covalency of five and a most extreme covalency of six, which is also known as extended covalency. This is possible due to the close proximity of vacant \({\rm{d}}\)-orbitals in the valence shell. Every group \(15\) element compound with a \(+5\) oxidation state is covalent.

Summary

Group \(15\) elements are also known as the nitrogen family. Nitrogen \(\left( {\rm{N}} \right),\) phosphorus \(\left( {\rm{P}} \right),\) arsenic \(\left( {{\rm{As}}} \right),\) antimony \(\left( {{\rm{Sb}}} \right),\) and bismuth are all members of the nitrogen family \(\left( {{\rm{Bi}}} \right).\) In their outer shell, all Group \(15\) elements have the electron configuration \({\rm{n}}{{\rm{s}}^2}{\rm{n}}{{\rm{p}}^3},\) where \({\rm{n}}\) is the primary quantum number. The nitrogen family is located in the \({\rm{p}}\)-block in Group \(15.\) The lightest component of group \(15,\) like group \(14,\) is nitrogen, which is found in nature as a element. Phosphorous is mostly obtained from phosphate rock and remains of fossil life forms. In the earth’s crust, arsenic, antimony, and bismuth are mostly found as sulphide minerals.

FAQs on Occurrence of Group 15 Elements

Q.1. What is the trend of atomic and ionic radii down the group in group 15 elements?
Ans: The ionic and atomic radii increase as you move down the group due to the expansion of another main energy level in each advancing element.

Q.2. What is the change in the oxidation state of group 15 elements while moving down the group and why?
Ans: Group \(15\) elements show a basic negative oxidation state of \(- 3.\) The likelihood of displaying a \(- 3\) oxidation state decreases as one moves along the group. This is due to the expansion of the nuclear size and the metallic character of the nucleus. By forming covalent bonds, Group \(15\) elements also show positive oxidation states of \(+3\) and \(+5.\) Because of the inert pair effect, the stability of the \(+5\)-oxidation state decreases as one moves down the group, while the stability of the \(+3\) oxidation state increases.

Q.3. What is the trend of the melting point of group 15 elements?
Ans: Because of the continual increase in nuclear size, the melting point increases from nitrogen to arsenic. The high melting point of arsenic, on the other hand, is attributed to its goliath layered structure. Despite the fact that the size of the nuclear nuclei increases from arsenic to antimony, their melting points decrease. Antimony, despite having a layered structure, has a lower melting point than arsenic due to the general pressing of particles. Furthermore, owing to the loose packing of atoms caused by metallic holding, bismuth has a lower melting point than antimony. 

Q.4. What is the other name of group 15 elements?
Ans: Group \(15\) elements are also known as the nitrogen family. Nitrogen \(\left( {\rm{N}} \right),\) phosphorus \(\left( {\rm{P}} \right),\) arsenic \(\left( {{\rm{As}}} \right),\) antimony \(\left( {{\rm{Sb}}} \right),\) and bismuth are all members of the nitrogen family \(\left( {{\rm{Bi}}} \right).\) In their outer shell, all Group \(15\) elements have the electron configuration \({\rm{n}}{{\rm{s}}^2}{\rm{n}}{{\rm{p}}^3},\) where \({\rm{n}}\) is the primary quantum number. The nitrogen family is located in the \({\rm{p}}\)-block in Group 15.

Q.5. Discuss the ionisation energy of group 15 elements.
Ans: When compared to group \(14\) elements, these elements have higher ionisation enthalpy values. Their larger atomic charge, lower nuclear radii, and stable half-filled electronic setups account for this. The ionisation enthalpy values decrease as we travel down the group. This is due to the increasing size of the nuclear nucleus.

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