11 topics with brief reviews: definitions, key facts, and class questions.
In this chapter, we analyze the chemistry of group VA elements—the pnictogens. The main focus is on two macroelements of utmost importance for biochemistry and medicine: nitrogen and phosphorus. You will study their general characteristics, physicochemical properties, and key classes of inorganic derivatives.
The section consistently covers oxidized nitrogen compounds (including nitrous acid and nitrites, which are of immense toxicological significance), as well as phosphorus chemistry. For the latter, phosphine, phosphides, halides, oxides, and the full spectrum of acids are discussed in detail. Special attention is paid to phosphates—the basis of bone tissue and a critical component of intracellular buffer systems.
During colloquia and exams, professors most frequently ask about the redox duality of nitrites, the hydrolysis of phosphorus halides, and the disproportionation reactions of nitrogen oxides. Be sure to master the structure of phosphorus acids—failing to know their basicity is the most common reason for losing points.
The nitrogen atom lacks a vacant d-sublevel in its outer energy level, making the unpairing of s-electrons and the formation of five covalent bonds impossible. The maximum covalency of nitrogen is four.
Why does nitrogen never exhibit a valence of V?
The nitrogen atom lacks a d-sublevel in its outer electron shell. Because of this, it cannot enter an excited state and unpair its s-electrons to form five bonds.
Why does an ammonia solution exhibit basic properties?
In the ammonia molecule, a lone electron pair is present on the nitrogen atom, capable of acting as a donor for a water proton, releasing hydroxide ions.
Why are oxidation states in nitrogen oxides called average values?
In complex oxides, such as N₂O or N₂O₃, the nitrogen atoms within a single molecule are in different electronic states and have different environments. Therefore, the oxidation state assigned to them is a mathematical average.
Strong sulfuric acid will displace weak nitrous acid, which will immediately decompose into water and nitrogen(III) oxide.
Strong sulfuric acid will displace weak nitrous acid, which will immediately decompose into water and nitrogen(III) oxide.
Why is hydrogen not evolved during the reaction of nitric acid with metals?
In an acidic medium, the nitrate ion is a much stronger oxidizing agent than the hydrogen ion. Therefore, electrons from the metal are accepted by nitrogen, forming various oxides or ammonium salts, while hydrogen is bound into water.
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