Quantitative Analysis: Nitrogen and Halogens

Introduction

Nitrogen is an atomic element with the atomic number 7 and the symbol N. Daniel Rutherford, a Scottish physician, was the first to discover and isolate it in 1772. Halogens are a group of five or six elements in the periodic table that are chemically related: Fluorine (F), Chlorine (Cl), Bromine (Br), Iodine (I), and Astatine (At). Tennessine (Ts), a manufactured element, can be a halogen. This group is known as group 17 in modern IUPAC nomenclature.

Nitrogen and its properties

Nitrogen is the lightest element in periodic table group 15, also known as the pnictogens. It is a common element in the universe, with an estimated total abundance of about seventh in the milky way and the solar system. 

Two atoms bind to form dinitrogen, a colourless and odourless diatomic gas with the formula N2 at standard temperature and pressure. Dinitrogen is the most abundant uncombined element; hence nitrogen in the atmosphere amounts for roughly 78% of the Earth’s atmosphere. 

Nitrogen is found in all organisms, most notably amino acids (and thus proteins), nucleic acids (DNA and RNA), and the energy transfer molecule adenosine triphosphate. 

Nitrogen makes up about 3% of the human body’s mass, making it the fourth most abundant element after oxygen, carbon, and hydrogen. The nitrogen cycle describes how nitrogen moves from the atmosphere to the biosphere and organic compounds and back again.

There are seven electrons in a nitrogen atom. They are arranged in the electron configuration in the ground state 1s22s22px12py12pz1 . As a result, the 2s and 2p orbitals contain five unpaired valence electrons (the p-electrons). 

It has one of the highest electronegativities (3.04 on the Pauling scale), with only chlorine (3.16), oxygen (3.44), and fluorine (3.98). (The light noble gases, helium, neon, and argon, are also more electronegative and appear on the Allen scale.)

There are many uses of nitrogen. For example, a common cryogen is liquid nitrogen. This colourless fluid resembles water in appearance but has 80.8 percent density (the density of liquid nitrogen at its boiling point is 0.808 g/mL). 

Nitrogen can be found in many organic compounds, used in high-strength fabric, and cyanoacrylate, used in superglue. As a result, nitrogen can be found in almost every primary drug class, including antibiotics.

Halogens and their properties

The halogen group is the only periodic table group containing elements in three of the four primary states of matter at standard temperature and pressure. When halogens are bonded to hydrogen, they all react to form acids.

Majority of halogens are derived from minerals or salts. The middle halogens—chlorine, bromine, and iodine—are frequently used as disinfectants. The most common type of flame retardant is organobromine, whereas elemental halogens are hazardous and lethally toxic.

The chemical bond energy of the halogens moves from top to bottom of the periodic table column, with fluorine deviating slightly. It has the highest bond energy in other atom compounds. This means that the reactivity of elements decreases as one moves down group 17 in the periodic table due to the increasing size of the atoms.

Halogens are highly reactive and can be harmful or lethal to biological organisms in large enough quantities. The high electronegativity of atoms due to their highly effective nuclear charge causes their high reactivity. 

Because halogens have seven valence electrons in their outermost energy level, they can gain an electron by reacting with the atoms of other elements to satisfy the octet rule. 

Fluorine is the most reactive element; it has a higher electronegative potential than oxygen, attacks otherwise inert materials like glass, and forms compounds with otherwise inert noble gases. It is a toxic and highly corrosive gas. 

When used or stored in laboratory glassware, fluorine’s reactivity is such that it can react with glass in the presence of small amounts of water to form silicon tetrafluoride.

The halogen group is the only periodic table group containing elements in three of the four primary states of matter at standard temperature and pressure. All halogens react to form acids when they are bonded to hydrogen. 

The vast majority of halogens come from minerals or salts. The middle halogens—chlorine, bromine, and iodine—are frequently used as disinfectants. Organic Bromides are the most common type of flame retardants, whereas elemental halogens are hazardous and lethally toxic.

Lassaigne’s test for nitrogen and halogens

It is an all-encompassing test for detecting halogens, nitrogen, and sulphur in organic compounds. Covalent bonds exist between these elements and organic compounds. These must be converted into ionic forms to be detected. 

To accomplish this, an organic compound is combined with sodium metal. Ionic compounds produced during fusion are extracted in an aqueous solution and detected using simple chemical tests. The extract is also known as Lassaigne’s extract and sodium fusion extract.

Test for Halogens

When chlorine is present, a white curdy precipitate is formed, soluble in an ammonium hydroxide solution.

Na + Cl → NaCl

NaCl + AgNO3 → AgCl + NaNO3

Bromine produces a yellowish-white precipitate that is only sparingly soluble in ammonium hydroxide solution.

Na + Br → NaBr

NaBr + AgNO3 → AgBr + NaNO3

A yellow precipitate forms in the presence of iodine insoluble in ammonium hydroxide solution.

Na + I → NaI

NaI + AgNO3 → AgI + NaNO3

Test for Nitrogen

When the carbon and nitrogen in an organic compound react with sodium metal, sodium cyanide (NaCN), water-soluble, is formed. Enough ferrous sulphate is added to convert this to sodium ferrocyanide. When ferric ions produced during the process react with ferrocyanide, Prussian blue ferric ferrocyanide precipitate is formed.

Na + C + N → NaCN

6NaCN + FeSO4 → Na4[Fe(CN)6] + Na2SO4

Na4[Fe(CN)6] + Fe3+ → Fe4[Fe(CN)6]3

Conclusion

Nitrogen-containing compounds include ammonia, nitric acid, organic nitrates (propellants and explosives), and cyanides. The powerful triple bond dominates nitrogen chemistry in elemental nitrogen, the second strongest bond in any diatomic molecule after carbon monoxide (CO). This makes it difficult for organisms and industries to convert  into valuable compounds. Still, it also means that burning, exploding, or decomposing nitrogen compounds to form nitrogen gas releases a significant amount of energy, which is often helpful. Synthetic ammonia and nitrates are necessary industrial fertilisers, and fertiliser nitrates contribute significantly to the eutrophication of water systems.