Oxidation State of Group 15 Elements

This image of the periodic table highlights the Group 15 and its members (nitrogen, phosphorus, arsenic, antimony, bismuth and moscovium)

Chemical Properties of Group 15 Elements

In chemistry, groups of elements refer to different columns of elements in the periodic table. There are in total 18 groups that are numbered in the periodic table from left to right. The f-block column of the periodic table is still not numbered as a group.

Out of the 18 numbered groups, we are going to talk about the group 15. Group 15 consists of the p-block elements (the block in the periodic table is an arrangement or set of elements on the basis of their valence electrons). The p-block is situated on the right-hand side of the table. The group 15 elements include nitrogen, phosphorus, arsenic, antimony, and bismuth.

The members of the group 15 show similar patterns in their electronic configuration, especially in their outermost shell. All these elements have 2 electrons in their subshell, and all of their outermost shells consist of 5 electrons.

The two most important elements of this group are Nitrogen and Phosphorous. Nitrogen, which occurs in a free state as a gas that is diatomic, constitutes more than 70% of the volume of air. Phosphorous is an element of life- its forms are present in our RNA and DNA. It is also present in bone marrows. 

The Trends In Chemical Reactivity of the Group 15 Elements

Here we will discuss the trends in chemical reactivity of the group 15 elements, i.e. nitrogen, phosphorus, arsenic, antimony, and bismuth. 

Elements of a group in the periodic table have similar patterns in their configuration of electrons. This similarity results in the formation of different trends in the chemical reactivity of the elements. Similarly, the elements of group 15 have a similar electron configuration- all of them have 2 electrons in their subshells and 5 electrons in their outer shells. This leads to the patterning of trends in their reactivity. Like as we go down the group (from Nitrogen to Bismuth), the metallic character of the elements increases and the ionization enthalpy (the amount of energy required to lose an electron) character of the elements decreases.

The covalent character (sharing of electrons) of the atoms decreases as we move down the group.

Group 15 elements are used in forming hydrides (compounds of hydrogen with any other element). Formation of NH3 (Ammonia), BiH3 (Bismuthine), PH3(Phosphine), AsH3 (Arsine) and SbH3 (Stibine) occurs.

Group 15 elements also form Halides (compounds formed with halogen atoms and any element). The halide is usually trihalides and pentahalides, for e.g. Phosphorus trichloride (PCl3) and Phosphorous pentachloride (PCl5).

Group 15 elements form oxides like Nitric Oxide, Bismuth Oxychloride, etc. The oxides are formed by the oxidation process (loss of electrons during a reaction) under different oxidation states of p block elements. H2

Since the atomic size increases as we move down, the melting point also gradually increases. Nitrogen has the least melting point in the group, and as we move to Arsenic and Phosphorus, the melting point starts to increase. There is a decrease in the trend from antimony onwards. This occurs because of the loose structure of atoms in the bonding. 

The boiling point of the elements regularly increases as we move down, and so does the density of the elements. 

Oxidation States of Group 15 Members 

The number of electrons in the outermost shell of the group 15 members is 5. In order to make it an octet configuration, it requires 3 more electrons. Therefore, it needs to gain 3 more electrons or share 3 electrons with the help of the covalent bonds. Therefore, the more common oxidation for these elements is the -3 oxidation which means adding 3 more electrons. The tendency to produce the -3 oxidation decreases as we move down the group. This happens because of the increase in metallic character and the atomic size of the elements. -3 oxidation state is used by reacting the group 15 members with hydrogen to produce ammonia, phosphane, arsane, stibane, and bismuthine. As we go down the group, these hydrides become more toxic and less stable. 

The +3 oxidation and +5 oxidation state occur by sharing electrons. In +3 oxidation, this sharing can occur through covalent bonds, in case of- nitrogen, arsenic and phosphorus. E.g. Nitrogen trichloride, phosphorus trichloride, arsenic trichloride or ionic bonds, in case of antimony and bismuth. E.g. Antimony trifluoride and Bismuth trifluoride. As we move down the group, the covalency character of the elements decreases.

The +5 oxidation state for nitrogen forms the N2O5. The true +5 oxidation occurs in phosphorus, arsenic, and antimony. Phosphorus even produces oxyhalides. 

Other Oxidation States for Group 15 Elements

Nitrogen can form various oxides under oxidation states +2, +4 and very unstable +6.

Antimony can produce a compound under the oxidation state of +2.

Phosphorus in phosphoric acid has the +1 oxidation state, and in hypo phosphoric acid, it has an oxidation state of +4.

FAQ (Frequently Asked Questions)

1. Is Nitrogen Fluoride a true example of +5 oxidation state for group 15 members?

When compared with the rest of the Group 15, due to the highest electronegativity it possesses, NItrogen is regarded as the most non-metallic of the group. The most common oxides of NItrogen are +5, +3, and -3. The oxyacids and oxides of Nitrogen comprise of nitrogen oxide, nitrogen dioxide, and nitrous oxide, all of which have different practical applications. As far as Nitrogen Fluoride is concerned, it is indeed an example of +5 oxidation state for group 15 members. But this example is only theoretical as the compound has not been synthesized yet. You can use the example of N2O5 also.

2. Are pnictogens and the elements of group 15 one and the same thing?

The greek word for suffocation or choking is “Pnico,” now as all the elements of Group 15 produce suffocating effects, they are also known as pnictogens. Group 15 is also known as Nitrogen family. The elements of this group exhibit similar patterns in the configuration of the electrons. All the components of this group have 5 electrons in the outermost shell, 2 electrons in the s subshell and 3 unpaired electrons in the p subshell. Yes, any element of the group 15 of the periodic table is also called a pnictogen because the elements belong to the nitrogen family or nitrogen group of elements (nitrogen, phosphorus, arsenic, antimony, bismuth and moscovium).