Group 15 is referred to as the Pnictogen family. Group 15 includes Nitrogen (N), Phosphorus (P), Arsenic (As), Antimony (Sb), Bismuth (Bi) and Moscovium (Mc). All elements in Group 15 share the same arrangement of p-orbitals, a half-filled s-orbital, and five valence electrons. These elements are often obtained from minerals. They are also present in the earth’s crust in elemental form (Tokitoh, 2000).
1. Electronic configuration of Group 15 elements
The valence shell of group 15 elements is ns2 np3, which is a symmetrical configuration of the p-subshell with three electrons. General electronic configuration of group 15 is ns2 np3 while the electronic configuration of group 15 members is as follows (Ellis & Macdonald, 2007).
N  1s2 2s2 2p3 or [He] 2s2 2p3
P  1s2 2s2 2p6 3s2 3p3 or [Ne] 3s2 3p3
As  1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p3 or [Ar] 3d10 4s2 4p3
Sb  1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p3 or [Kr] 5s2 4d10 5p3
Bi  1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f14 5d10 6p3 or [Xe] 6s2 4f14 5d10 6p3
Mc  1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f14 5d10 6p6 7s2 5f14 6d10 7p3 or [Rn] 7s2 5f14 6d10 7p3
2. Characteristics of Group 15 elements
2.1. Oxidation state of Group 15 elements
• The nitrogen family shows a wide range of oxidation states .Generally, all elements in group 15 have five valence electrons. However, some elements in the group have variable oxidation states. The most common oxidation states of group 15 elements are +5, +3, and -3. The +3 oxidation state is more common than the +5 oxidation state.
• The +5 oxidation state is a rare state, and it only forms with certain highly electronegative atoms. However, the oxidation state of group 15 elements is not very different from the oxidation state of other elements.
• The group 15 elements can form binary compounds with metals. Trivalent pnicogens are Lewis * bases. The oxidation state of the metal in group 15 compounds is -3. However, the covalent character of group 15 elements reduces as we move down the group.
2.1. Inert pair effect
• Among the heavier elements of Group 15, the inert pair effect is one of the major factors that influence their oxidation states. Inert pair effect is dominant in lead
• The atoms of Group 15 are polyatomic and the oxidation states range from +3 to +5. The pnictogens, or nitrogen family, are also known as nitrogen elements. The lighter elements of the group, such as nitrogen, are non-metals. However, as the group progresses, the metallic aspect becomes more apparent.
3. Anomalous behavior of Nitrogen
• Among the elements of the periodic table, Nitrogen is known for its anomalous behavior. It has a high electronegativity, has no d-orbitals in its outermost shell and a high ionization enthalpy. It may take on many different oxidation states and participate in many chemical bonds. It can form triple bonds and pp-p multiple bonds with high electronegative elements (Schulz, 2015).
• Nitrogen possesses a weak N-N bond because of strong inter electronic repulsions. It also exhibits a high electronegativity difference. This difference makes it polar. It can form an As-As single bond, but it is weaker than a P-P bond.
• Nitrogen also exhibits an anomalous behavior when it comes to hydrogen bonding. It can form hydrogen bonds with itself in hydride compounds. However, other elements in this group cannot form hydrogen bonds. They also show a low polar character.
• Nitrogen forms a variety of oxides. These oxides are dimeric and have a wave function sign. Nitrogen also forms a tri negative ion N3-, but it is not present in other elements.
• Nitrogen has an anomalous behaviour in that it has high electronegativity and is an electron-pair donor. It also forms a high number of oxides, but it lacks a penta halide.
4. Trend in the physical properties of Group 15 Elements
Compared to group 14, the physical properties of Group 15 elements are generally more favorable. They show a wider range of allotropic structure, have a more stable valence shell and exhibit a higher ionization enthalpy. As the group goes down, the basic character of the oxides decreases, and the reducing character increases. This is due to the d-orbitals of the trihalides being vacant. The hydrides also exhibit a regular gradation in properties (Tokitoh, 2000).
4.1. Atomic and ionic radii
Atomic radii of group 15 elements increase from nitrogen to bismuth gradually similarly ionic radii also increase from N3- to Bi5+ only difference is in their ions due to change in non-metallic to metallic character. These data are unknown for Moscovium, at the moment.
Figure 1: Atomic radius of Group 15 elements
Figure 2: Ionic radius of Group 15 elements
4.2. Ionization energy
Ionization energy of Group 15 elements decrease from Nitrogen to Bismuth.
Ionization energy of group 14 elements in kilo joule per mole
Figure 3: First Ionization Energy of the Group 15 elements
Electronegativity of group 15 elements decrease nitrogen to antimony while antimony and bismuth has same electronegativity. Similarly, electronegativity of Moscovium is unknown.
4.4. Melting and boiling point
Melting point of group 15 elements show irregular behavior while boiling point increase from nitrogen to bismuth with the exception of Moscovium
Figure 4: Melting and Boiling Points of the Group 15 elements
5. Chemical properties
Among the polyatomic elements, the chemical properties of group 15 elements are relatively diverse. The elements also share three electrons that can be used for covalent bonds. This arrangement allows group 15 elements to form simple hydride molecules. Most of their chemical properties are determined by their outermost electron shell (Ellis & Macdonald, 2007).
5.1. Reaction with oxygen
Group 15 elements react with oxygen and form different oxides such as:
Scheme 1: Reaction of Group 15 elements with Oxygen
5.2. Reaction with Metals
Metals reacts with group15 elements and form different compounds such as nitride and phosphide
Scheme 2: Reaction of Group 15 elements with water
5.3. Reaction with halogens
Elements of group 15 reacts with halogen and form trihalides
Scheme 3: Reaction of Group 15 elements with halogens
You want to know about all the Groups of the Periodic Table?
1. Ellis, B. D., & Macdonald, C. L. (2007). Stable compounds containing heavier group 15 elements in the+ 1 oxidation state. Coordination chemistry reviews, 251(7-8), 936-973.
2. Schulz, S. (2015). Covalently bonded compounds of heavy group 15/16 elements–Synthesis, structure and potential application in material sciences. Coordination Chemistry Reviews, 297, 49-76.
3. Tokitoh, N. (2000). New aspects in the chemistry of low-coordinated inter-element compounds of heavier Group 15 elements. Journal of Organometallic Chemistry, 611(1-2), 217-227.