What are elements of Group 15?

The 3rd group of the elements of p-block is group 15. The elements are otherwise called as nitrogen family/pnictogen. The elements which are components of the nitrogen family are nitrogen, phosphorus, arsenic, antimony, and bismuth. The elements of the nitrogen family are named as representative elements as they are kept on right region of the main periodic table. The nature of elements found in the nitrogen family is metal, metalloids, and non-metals. The reason why this group is called as nitrogen family as first element present in this group is nitrogen.

Where do Group 15 elements occur?

The elements of group 15 are phosphorus, nitrogen, bismuth antimony, and arsenic. The most abundant element which is present in the air is nitrogen and the percentage of nitrogen present in the air is 78%. In the free state, the elemental nitrogen is present as diatomic gas (N₂). In the organic matter obtained from plants and animals, phosphorus is the dominant element present. In nucleic acids, phosphate groups are present. Phosphates are also found in teeth and bones. The other elements arsenic, bismuth, and antimony are found as sulfides. Arsenopyrite, bismuth glance, and stibnite are examples of sulfides of arsenic, bismuth, and antimony respectively.

Elements of Group 15 in periodic table

Nitrogen

The first element is nitrogen. Its atomic number is seven and appears as gas, which has no taste, no color, or no odor. It appears non-metal and occupies 78% of the atmosphere on basis of volume. 1s²2s²2p³  is the electron structure of this element and no d-orbitals are seen. No allotropic forms are seen in diatomic nitrogen. Several nitrogen compounds are formed from unusually stable N₂(g). Among nitrogen atoms, the bond is a triple covalent bond, which cannot be broken easily. Nitrogen dioxide, nitrous oxide, and nitrogen oxide are covalent compounds. The most important nitrogen-containing compound is NaNO₃. +5,+3, and -3 are the oxidation states.

Phosphorus

In the nitrogen family, the second element is phosphorus and is a non-metal. -3  is the familiar oxidation state. The electron structure of phosphorus is [Ne]3s²3p³. The compounds of phosphorus are obtained from rocks which has phosphorus. White phosphorus and red phosphorus are the two allotropic types of phosphorus. A white solid that is waxy and could be split into pieces using a knife is white phosphorus. A tetrahedral molecule is formed by phosphorus. White phosphorus is not stable in nature. A chain, which is near to polymeric structure is red phosphorus. The latter one’s stability is higher than the former one. When the reactivity is compared, the reactivity of red phosphorus is low. Red phosphorus is not toxic but white phosphorus is toxic. Phosphoric acid is utilized as fertilizer and is a significant compound of phosphorus.

Arsenic

The third member of group 15 is arsenic. It is a metalloid, which is extremely poisonous. The electron structure is [Ar]3d¹⁰4s²4p³. Because of its metalloid property, the density is high, thermal conductivity is minimum, and has the minimum capacity for the conduction of electricity. +5,+3,+2,+1, and -3 are the oxidation states of this element. Yellow arsenic, gray arsenic, and black arsenic are allotropic forms. Among these allotropic forms, gray arsenic is the known allotrope. The uses of arsenic compounds are alloys, killers of weed, and insecticides. By heating arsenic comprising of sulfides, the element arsenic could be obtained.

Antimony

The fourth member of group 15 is antimony. This element comes under metalloid. The electron structure is [Kr]4d¹⁰5s²5p³. +5,+3, and -3 are the oxidation states. The ores of antimony sulfides are used to obtain antimony and at temperatures, which are low, they get vaporized easily. With the help of antimony and arsenic, alloys could be made. Semiconductors that are employed in electronic gadgets are made from antimony and arsenic.

Bismuth

The fifth element of group 15 is bismuth. This element is metal. [Xe]4f¹⁴5d¹⁰6s²6p³ is the electronic configuration. Similar to antimony and arsenic, bismuth exhibits poor metallic properties. Compounds of bismuth are employed in medicine and cosmetic products. Because of low ionization energy and the least electronegativity, an electron is lost readily than other groups 15 elements. This states the reason for the metallic nature of bismuth.

Periodic trends of Group 15 elements

The periodic trends of group 15 elements found in the p-block are given as:

Atomic Radii

On moving downwards to the group, there would be an increment in atomic radius and ionic radius which is owing to the addition of new orbitals. But from arsenic to bismuth, the increment in ionic radius is very small, owing to d orbitals or f orbitals which are completely filled.

Electronic configuration

The behavior of an element could be predicted by the outer shell electronic structure. For group 15 elements, the outer shell electronic structure is ns²np³. The arrangement is the same for all elements and due to the same arrangement, they exhibit similar properties. In group 15, the s-orbitals are completely filled, and the extra stability is by virtue of p-orbitals, which are half-filled.

Ionization enthalpy

The quantity of energy essential to eliminate an electron from the valence orbit of an atom is ionization energy. When the electron is nearby to the nucleus, the hold is stronger, and the energy essential would be higher. On moving towards the bottom of the group, there would be a rise in atomic radius; and ionization energy reduces.

Electronegativity

When there is an increase in the size of an atom, the electronegativity reduces on moving bottom of the group.

Melting points and Boiling points

Due to a steady increment in the size of the nucleus, the melting point begins to rise from nitrogen to arsenic. Due to discrete diatomic molecules of nitrogen, the nitrogen’s melting point is low. There is a reduction in melting point from arsenic to antimony. The presence of free pressing of particles accounts for the lesser melting point of antimony when compared to arsenic. As the atoms are loosely packed by metallic bonding in bismuth, the melting point of bismuth is less when compared to antimony.

The boiling point rises from nitrogen to bismuth. Also, the density rises ongoing downwards the group.

Properties of Group 15 elements

In this group, the five elements are polyatomic in nature. Nitrogen exists as gas, ongoing downwards the group; there will be increment in metallic nature. The non-metallic elements are phosphorus and nitrogen, the metallic element is bismuth, and metalloids are arsenic and antimony. Other than nitrogen, the balance elements exist in allotropic forms. On moving to the bottom of the group, the stability of +5 oxidation state is reduced whereas there is a rise in the +3 oxidation state stability because of the inert pair effect.

Context and Applications

This topic is important for undergraduate courses particularly for bachelors in chemistry and other competitive exams like olympiad exams.

Practice Problems

Question 1: Which of the element listed is seen in a mono-atomic state?

1. Nitrogen
2. Arsenic
3. Bismuth
4. Phosphorus

Answer: Option (3) is correct.

Explanation: Bismuth is seen in a monoatomic state because its catenation tendency is weak.

Question 2: Name the element, which is a member of the group 15 element.

1. Uranium
2. Xenon
3. Moscovium
4. Radon

Answer: Option (3) is correct.

Explanation: Moscovium is a member of group 15 in addition to nitrogen, antimony, bismuth, phosphorus, and arsenic.

Question 3: Give the maximum covalency of the atom N.

1. Two
2. Three
3. Four
4. One

Answer: Option (3) is correct.

Explanation: Nitrogen could give up to 4 electrons, three electrons in p subshell and one from s-subshell. As d-orbitals are restricted, the covalency is four. Option (3) is correct.

Question 4: Which of the following is the chemical name of chile saltpetre?

1. Sodium nitrate
2. Sodium nitrite
3. Potassium nitrate
4. Potassium nitrite

Answer: Option (1) is correct.

Explanation: The chemical formula of chile saltpetre is NaNO₃. So, sodium nitrate is the name of chile saltpetre.

Question 5: Which of the following is pyrophosphoric acid’s chemical formula?

1. H₄P₂O₇
2. H₃PO₄
3. H₃PO₃
4. H₄P₂O₅

Answer: Option (1) is correct.

Explanation: Pyrophosphoric acid is also called diphosphoric acid. Its chemical formula is H₄P₂O₇.