Why the chemical reactivity of nitrogen is much less than phosphorus?
Answers
The chemistry of nitrogen is dominated by the ease with which nitrogen atoms form double and triple bonds. A neutral nitrogen atom contains five valence electrons: 2s2 2p3. A nitrogen atom can therefore achieve an octet of valence electrons by sharing three pairs of electrons with another nitrogen atom.
Because the covalent radius of a nitrogen atom is relatively small (only 0.070 nm), nitrogen atoms come close enough together to form very strong bonds. The bond-dissociation enthalpy for the nitrogen-nitrogen triple bond is 946 kJ/mol, almost twice as large as that for an O=O double bond.
The strength of the nitrogen-nitrogen triple bond makes the N2 molecule very unreactive. N2 is so inert that lithium is one of the few elements with which it reacts at room temperature.
6 Li(s)+N2(g)2 Li3N(s)In spite of the fact that the N2 molecule is unreactive, compounds containing nitrogen exist for virtually every element in the periodic table except those in Group VIIIA (He, Ne, Ar, and so on). This can be explained in two ways. First, N2 becomes significantly more reactive as the temperature increases. At high temperatures, nitrogen reacts with hydrogen to form ammonia and with oxygen to form nitrogen oxide.
N2(g)+3 H2(g)2 NH3(g)N2(g)+O2(g)2 NO(g)Second, a number of catalysts found in nature overcome the inertness of N2 at low temperature.
The Synthesis of Ammonia
It is difficult to imagine a living system that does not contain nitrogen, which is an essential component of the proteins, nucleic acids, vitamins, and hormones that make life possible. Animals pick up the nitrogen they need from the plants or other animals in their diet. Plants have to pick up their nitrogen from the soil, or absorb it as N2 from the atmosphere. The concentration of nitrogen in the soil is fairly small, so the process by which plants reduce N2 to NH3 or "fix" N2 is extremely important
Phosphorus is the first element whose discovery can be traced to a single individual. In 1669, while searching for a way to convert silver into gold, Hennig Brand obtained a white, waxy solid that glowed in the dark and burst spontaneously into flame when exposed to air. Brand made this substance by evaporating the water from urine and allowing the black residue to putrefy for several months. He then mixed this residue with sand, heated this mixture in the presence of a minimum of air, and collected under water the volatile products that distilled out of the reaction flask.
Phosphorus forms a number of compounds that are direct analogs of nitrogen-containing compounds. However, the fact that elemental nitrogen is virtually inert at room temperature, whereas elemental phosphorus can burst spontaneously into flame when exposed to air, shows that there are differences between these elements as well. Phosphorus often forms compounds with the same oxidation numbers as the analogous nitrogen compounds, but with different formulas, as shown in the table below.
Nitrogen and Phosphorus Compounds with the Same Oxidation Numbers but Different Formulas