Preparation
Nitrogen
In industry nitrogen is prepared|received| by fractional distillation of liquid|rare,thin| air. Nitrogen (b.p. = -195.8оС) is the most volatile|flying| air component, therefore nitrogen and noble gases evaporate from liquid air first of all. The noble gases do not interfere with the use|utillizing| of nitrogen for creation|making| of inert atmosphere in chemical and other processes. To remove| the admixtures of oxygen (some few|a little| %, b.p. of O2= -183оС) nitrogen gas is treated chemically, by passing it through the system with the heated metallic copper. Thus practically all О2 admixture is chemically bound into СuO.
In laboratory:
1. heating of mixture of concentrated solutions of :
NH4Cl + NaNO2 = N2 + 2H2O + NaCl
2. thermal decomposition of ammonium nitrite
NH4NO2 = N2 + 2H2O
3. thermal decomposition of azides| of metals (the purest N2 preparation method):
2NaN3 = 2Na + 3N2
Phosphorus
In industry: in electric furnace by the reaction:
2Ca3(PO4)2 + 10C + 6SiO2 = P4 + 6CaSiO3 + 10CO
This overall process involves two stages:
Ca3(PO4)2 + 3SiO2 = P2O5 + 3CaSiO3
2P2O5 + 10C = P4 + 10CO
Phosphorus vapours that have been already formed are then condensed under the layer of water. The product of condensation is white phosphorus.
Arsenic Antimony Bismuth
To produce elemental As, Sb, and Bi their sulfide ores are annealed in air to form oxides. The next stage is usually reduction by coal.
Arsenic: thermal decomposition of arsenical pyrites
FeAsS FeS + As
or reduction of the oxide formed during burning of sulfide ore:
As2O3 + 3C = 2As + 3CO
Antimony: smelting iron sulfide:
Sb2S3 + 3Fe 2Sb + 3FeS
or consecutive process:
Sb2S3 + 5O2 Sb2O4 + 3SO2
Sb2O4 + 4C 2Sb + 4CO
Bismuth:
2Bi2S3 + 9O2 2Bi2O3 + 6SO2
Bi2O3 + 3C 2Bi + 3CO
Chemical properties
Nitrogen
Nitrogen is a non-metal, by its electronegativity (EN| = 3) and it is lower only |renounces|of F and O.
As a result of|because of,owing to| high thermal stability N2 does not burn|burning| and does not support|underprop| burning. However magnesium burns|burning| in the atmosphere of N2. It is explained by the fact|, that in the formation of nitride| at interaction of N2 with magnesium more energy is released then it is required for the break of N— N bond in the molecule of N2.
At ordinary|usual| conditions N2 directly|immediately| interacts only in a really unique reaction with lithium:
6Li + N2 = 2Li3N
Under conditions of activating of N2 molecules (at higher temperatures) it reacts with metals and non-metals, here nitrogen acts as|appear| an oxidant and only in reactions with F2 and O2 it behaves as a reductant.
Phosphorus
P is the second chief subgroup element of the fifth group. This is a typical non-metal by its EN value such as F, O, Cl, N and S.
Features of phosphorus chemistry:
1. The total of 1-5 ionisation potentials decreases sharply from N (266.8 eV) down to P (176.7 eV). This leads to the stabilisation of positive oxidation states, including the highest one (+5). Therefore, all compounds with oxidation states of P less than (+5) are reductants. At the same time, in aqueous solutions P+5 compounds are not oxidants. A reason is the larger stability of oxygencontaining compounds of phosphorus comparing with compounds of N. Instead, phosphorus compounds with hydrogen are less stable than those of N.
2. The valence capabilities of P are more diverse than of those N due to the presence of vacant 3d-orbitals of P. When excitated, P has 5 unpaired electrons that provide covalence 5 by the exchange mechanism. In addition, free 3d-orbitals can form covalent bonds with donor-acceptor mechanism. Therefore, there are new types of hybridization in case of P, e.g. sp3d (coordination number 5), sp3d2 (CN 6). These types are impossible for the atom of nitrogen.
3. P forms stable polymeric structures because single -bonds of phosphorus are stronger than -bonds of N (EN-N = 160.5; EP-P = 215; EAs-As = 134; ESb-Sb = 126; EBi-Bi = 104 kJ/mol). As a result, P polymers contain single bonds instead of monomers with multiple bonds like nitrogen.
4. Additional -bonding between atoms of phosphorus is realised. Thus, P atoms can form not only p-p- but also p-d- bonds, the latter predominate.
Phosphorus shows oxidation and reducing properties.
Examples of reducing properties are reactions with active non-metals and strong oxidants:
4P + 3O2 (lack) = 2Р2O3
4P + 5O2 (excess) = 2Р2O5
2Р + 5Сl2(excess) = 2РСl5
P + 5HNO3 = H3PO4 + 5NO2 + H2O
Oxidising properties it reveals at interaction with active metals are:
3Mg + 2P = Mg3P2
White P disproportionate in alkali solutions upon heating:
P4 + 3NaOH + 3H2O = PH3 + 3NaH2PO2 – hypophosphite
Arsenic, Antimony, Bismuth
Pure As, Sb and Bi in a compact state behave differently with regaid to oxygen. Sb and Bi are hardly oxidized under normal conditions in dry atmosphere. Arsenic darkens very quickly in the air with the formation of oxide, As2O3. It does not passivate the arsenic surface, so fine As can be oxidised completely.
When heated in the air, all these elements are oxidised to E(III):
4E + 3О2 = 2E2О3
In oxygen atmosphere under the same conditions:
As is oxidized to As(V) 4As + 3O2 = 2 As2O3
Oxidized to Sb (IV) 2Sb + 2O2 = Sb2O4
Bi is oxidized only to Bi(III) 2Bi + 3O2 = Bi2O3
These elements do not dissolve in water and organic solvents. Having a quite different structure compared with typical metals, As, Sb, and Bi do not usually form solid solutions with them. In general, the ability to form compounds with metals decreases in the series As(EN = 2.2) — Sb(EN = 1.82) — Bi(EN = 1.67) since EN decreases. Therefore, an eutectic mixture formation is more a characteristic feature of these elements.
Bi alloys are of particular interest because they have extremely low melting temperatures (for instance, Wood`s alloy: 50% Bi, Pb 25%, 12.5% Sn and 12.5% Cd, m.p. = 65-70 oC, i.e. below b.p. of water).
As, Sb, and Ві follow hydrogen in the electromotive series of metals (between Н and Cu), so they will not displace hydrogen of non-oxidant acids. However, they can be dissolved at the action of oxidants:
2As + 5Cl2 + 8H2O = 2H3AsO4 + 10HCl
or concentrated H2SO4, HNO3. The mechanism of interaction in both acids is different:
H2SO4: 2As + 3H2SO4(conc.) As2O3 + 3SO2 + 3Н2О
2Sb (Bi) + 6H2SO4(conc.) Sb2 (Bi) (SO4)3 + 3SO2 + 6Н2О
HNO3: 3As + 5HNO3(conc.) + 2Н2О 3H3AsO4 + 5 NO
(ortho-arsenic acid)
3Sb + 5HNO3(conc.) 3H3SbO4 + 5NO + Н2О
(-antimonic acid)
Bi is passivated in concentrated HNO3, and its behaviour is metallic in diluted nitric acid:
Bi + 4HNO3(dil.) Bi(NO3)3 + NO + 2Н2О
Note: Bi always forms a salt, which also confirms its metallic character.
As, Sb, and Bi do not react with strong alkali solutions. Sb and Bi are stable to alkali melts. On the other hand, arsenates are formed when melting of As with alkalis in the presence of oxidants:
2As + 5KNO3 + 6KOH = 2K3AsO4 + 5KNO2 + 3H2O (КОН or К2СО3)
With the exception of phosphorus trifluoride, these elements form their trihalides by direct combination of the elements, using an excess of the Group V element. Two series (EX3 and EX5) of As and Sb halides are known, whereas EX3 are characteristic of Bi (only BiF5 is known).