Hydrogen compounds

Nitrogen

Ammonia. It is a colourless gas with a suffocating smell. Toxic: irritates the mucous membrane, and|but| a sharp poisoning causes|call| the damage of eyes and lungs.

Structure. According to the hybridization theory the atom of nitrogen in NH₃ is in a state of sp³-hybridization.

The molecule of NH₃ is a three-cornered pyramid with the atom of nitrogen at the top| and three atoms of hydrogen at the base. Reason|cause| of such spatial arrangements|distributing| of bonds is|appear| a presence of unshared pair|couple| of electrons, which|what| makes a strong repulsive action|act| on the bonds|truss|:

(length of bond – 0.101 nm|, angle - 107^о).

Interestingly|curiously|, that stoichiometrically similar |molecule of BF₃ is|appear| flat. Boron|it| does not have a lone electronic pair|couple|, which|what| would cause|call| repulsion ||it|on the three two-electronic bonds and break the plane| location|disposition| of BF₃.

A remarkable property|virtue| of molecules of NH₃ is|appear| their ability|solvency| to|by| the structure inversion, i.e. «turning inside-outside» by passing the atom of nitrogen through a temporary plane formed by atoms of hydrogen located at the base of pyramid.

A potential barrier of this inversion is equal to 25 kJ/mol. Some molecules, which have attained sufficient energy, can realize this process|it| at every instant moment of time. As a result such inversion is related|tied| to the emission of strict certain|definite| frequency (=2.387^.10¹⁰ s^‑1|), based on that phenomena an apparatus was created for a very precise measuring of time. Such «molecular clock» allowed, in particular|including|, to discover that duration of the Earth days annually grows by 0.00043 secs.

Molecule of NH₃ is a strong donor of electronic pair|couple| and is characterized by|described| high polarity ( = 1.46 D), as electrons of bonds of N—H are strongly displaced from| H to|by| N. Polarity of the bond N—H explains |condition,cause| hydrogen bond formation between the molecules of NH₃. The presence of hydrogen bonds in liquid|rare,thin| and solid ammonia explains many of its|its| extraordinary properties|virtue| in compared to other hydrogen compounds|halving,compound,junction,joint,coupling| of V group elements. For this reason m.p. (-77.75 ⁰С) and b.p. (-33.42⁰) of NH₃ are comparatively high, it is characterized|described| by considerable enthalpy of evaporation and ammonia is liquefied| easily. That property of ammonia is thereon us|utillizing|ed in the machines|vehicle| of refrigerations.

Preparation.

In industry (synthesis process by Fritz Haber). The process involves direct combination of N₂ and H₂ under special conditions:

N₂ + 3H₂ 2NH₃  = -92.4 kJ/mol

(catalyst - Fe, 400-500⁰, pressure 1000 atm).

In a laboratory:

NH₄Cl + Ca(OH)₂  CaCl₂ + NH₃ + H₂O

Chemical properties|virtue|. By solubility in water NH₃ exceeds any|some| other gas: at 0^оС one 1 volume of water absorbs 1200 volumes of gaseous NH₃ and|but| 700 more volumes at 20⁰С. Wonderful solubility is based on the formation of intermolecular hydrogen bonds. Two mechanisms of the formation of hydrogen bonds are thus possible between the molecules of NH₃ and water. Since donor| property|solvency| of a molecule of NH₃ is expressed stronger than in water, and|but| the bond О—Н| is more polar in compared with the polarity of bond of N—H in NH₃, and the intermolecular| hydrogen bond forms according thethe first mechanism.

Thus|on this grow|, physical and chemical processes in water|aquatic| solution of NH₃ can be presented in such form|appearance|:

The formation of ОН-| ions creates an alkaline reaction in the solution of NH₃ in water. The constant of ionization is low (К = 2^.10^-5), preving that the equilibrium of this reaction is strongly displaced to the left (in 1М solution ammonia hydroxide is ionized only 0.4% NH₃ and Н₂О). The commercial|corrupt| concentrated solution of NH₃ usually has density|closeness,thickness| of 0.91 g/cm³ and contains|maintain| 25 mass| % NH₃ (that approached the composition of NH₃^.3Н₂О). At cooling of solutions of NH₃ can be isolated crystalhydrates| of NH₃^.H₂O, m.p. = -77^оС), 2NH₃^.H₂O (m.p. = -78^оС), NH₃^.2H₂O (m.p. = -97^оС), which|what| consist of chains of molecules of NH₃ and H₂O, bound together by hydrogen bonds|truss| in which molecules of NH₄OН are absent|what|. That is why|that is why| although solution of NH₃ in water is named|called| “ammonium hydroxide” this name is conditional, and a molecule of NH₄OH as an individual chemical does not exist. Thus|on this grow|, aqueous solutions of NH₃ have basic|main| characteristics not due to the formation of mythical compound|halving,compound,junction,joint,coupling| of NH₄OH, but because of|because of,owing to| the extraordinarily expressed donor| activity of atom of nitrogen in NH₃.

For NH₃ are characteristic|character,typical| reactions of three types|appearance|:

1. reactions of addition. An interaction of NH₃ with acids gives salts of ammonium:

NH₃ + H⁺ = NH₄⁺

NH₃ + HCl = NH₄Cl

(interestingly|curiously|, that reaction does not proceed|leaves| at complete absence of water!!!)

The ion of NH₄⁺ is and| most of its|its| salts are colourless. In the solid state|figure,camp,mill| the salts of ammonium form structures, characteristic|character,typical| of compounds with the considerable part|stake,share| of ionic bond. That is why|that is why| they are well dissolved in water and dissociate| almost completely. The structure of NH₄⁺ is tetrahedral|, in which|what| the peaks| of tetrahedron are occupied by the atoms of hydrogen, and|but| an atom of nitrogen is in the center.

A positive|staid| charge is evenly distributed between all atoms of hydrogen.

Ammonium salts at hydrolysis give acidic medium|Wednesday|

NH₄⁺ + H₂O = NH₄OH + H⁺

as NH₄OH is a weak base|foundation|.

Salts of ammonium are stable|firm| under ordinary|usual| conditions, but at heating are decomposed. Nature of the final|end| products product of thermal decomposition of ammonium salts is mainly determined by the properties|virtue| of anion|.

If an acid residue is a strong oxidant |remainder|, ammonium nitrogen is oxidized: in such reaction ammonium nitrogen gives|return| 4 electrons to nitrate anion nitrogen which|what| is|appear| an oxidant. On the other hand|on other hand|, this reaction is an example of intramolecular disproportionation|.

Other examples are:

NH₄NO₂ = N₂ + 2H₂O

(NH₄)₂Cr₂O₇ = Cr₂O₃ + N₂ + 4H₂O

3(NH₄)₂SO₄ = N₂ + 3SO₂ + 6H₂O + 4NH₃

If an acid is|appear| not an oxidant, the type|nature| of decomposition depends on its volatility at temperature of decomposition:

1. From the salts of non-volatile acids is eliminated only NH₃:

(NH₄)₃РO₄ = 3NH₃ + H₃РO₄

2. If an acid is volatile|flying| (for example HCl)

NH₄Cl = NH₃ + HCl

at cooling it again forms an initial|output| salt and process of decomposition looks like sublimation of salt.

In liquid|rare,thin| ammonia exist dimers (NH₃)₂ which|what| are able to|by| selfdissociate. However, this process is |it|extraordinarily moved to the left (at -50^оС):

(NH₃)₂ = NH₄⁺ + NH₂^- К = 2^.10^-33

2. reactions of substitution. The reactions of hydrogen substitution of ammonia are less characteristic|character,typical|, than the reactions of addition. They proceed at high temperatures. At substitution of one hydrogen in NH₃ it forms amides of metals MeNH₂, at substituting of two atoms of hydrogen –imides of | metals Me₂NH, at substituting of three atoms of hydrogen – nitrides of| metals.

Amides. Dry ammonia interacts with metals (in fusions):

2 + 2Na = 2NaNH₂ +  = -145 kJmol NaNH₂- amide|

Thus, here hydrogen of NH₃ lowers its oxidation state while NH₃ acts as an oxidant. On the other hand|on other hand|, this reveals| the acidic nature of NH₃|virtue|. Amides of metals are|appear| typical|model| salts of NH₃, which|what| correspond to its|its| acidic function. Acid nature of NH₃ is expressed very poorly, the constant of acid ionization extraordinary low (рК_а 35), that is why|that is why| salts of NH₃ as acids in water hydrolyse| completely:

NaNH₂ + H₂O = NaOH + NH₃

Imides. Dry ammonia interacts with metals (at fusion):

NH₃ + 2Li = Li₂NH + H₂; Li₂NH- lithium imide

Imides also can be prepared|received| by careful heating of amides|:

2LiNH₂ = LiNH + NH₃

Imides also correspond to the acidic function of ammonia.

Nitrides. At annealing| of solid Al in the atmosphere of NH₃ occurs a reaction:

2Al + 2NH₃ = 2AlN + 3H₂

this process of preparation of nitride| coating films is called nitridation|.

Nitrides of metals, unlike halides or| sulfides, are|appear| not salts, as they do not correspond to any|some,any| acids. They are formed at high temperatures:

3Mg + N₂ = Mg₃N₂

2B + N₂ = 2BN

Properties|virtue| of nitrides| more or less appropriately change according periods and groups of the periodic system. For example, in small periods there is observed a transition from| basic|main| nitrides |to|by| acidic ones:

Na₃N Mg₃N₂ AlN Si₃N₄ P₃N₅ S₄N₄ Cl₃N

basic|main| amphoteric| acidic

Nitrides are classified so: ionic (Li₃N), covalent| (NH₃) and “inclusion”|inclusion| (Fe₄N, Fe₃N). Nitrides of| s-elements have mostly ionic type of bonds|truss|, oxidation state of nitrogen there is -3. These nitrides| are crystalline compounds. They are chemically active, easily react with water:

Mg₃N₂ + 6H₂O = 3Mg(OH)₂ + 2NH₃

Nitrides BN, AlN, Si₃N₄ are polymeric compounds with high temperatures of melting (2000-3000^оС), they are dielectrics or semiconductors.

Nitrides of d-metals (Fe₄N, Fe₃N, Ni₃N) are compounds|halving,compound,junction,joint,coupling| with metallic bond, they have metallic (electronic) conductivity. They are products of squeezing of atoms of nitrogen into the holes of crystalline grate of metals. Filling of these empty space account for material strengthening, those nitrides are remarkably hard |, refractory|that is why|, chemically inactive, not reacting with water, only slowly|sluggishly| reacting with acids. The oxidation state of elements in them is accepted as equal to|equal| zero.

It is obvious, that from the covalent| nitrides| a greatest practical value|importance,meaning| has nitride| of hydrogen of NH₃- ammonia. Next to derivatives of metals are known the products of substituting of hydrogens of ammonia on a halogen, for example chlorous nitrogen of NСl₃, which|what| forms as yellow oily drops obtained at|receive|action act|act| action of Cl₂ on the concentrated solution of NH₄Cl:

NH₄Cl + 3Cl₂ = NCl₃ + 4HCl (1HCl + 3HCl)

NСl₃ is very unstable, at heating to|by| 90^оС or at slight blow|kick| it decomposes with an explosion on elements. In water NСl₃ is not dissolved, but slowly|sluggishly| hydrolysed|it|:

NCl₃ + 3H₂O = NH₃ + 3HOCl

3. Reactions of oxidation. The oxidation state of nitrogen (-3) in NH₃ is|appear| lowest, however |virtue| its reduction |its| activity is expressed very poorly: NH₃ does not burn|burning| in air, it does not react in solutions with most oxidants, for example with compounds|halving,compound,junction,joint,coupling| of Cr(VI). It is explained with the fact that NH₃ and ion of NH₄⁺ are comparatively stable molecules|firm|.

However NH₃ normally burns|burning| in the atmosphere of oxygen:

4NH₃ + 3O₂ = 2N₂ + 6H₂O

and|but| in the presence of catalysts in the air:

4NH₃ + 5O₂ = 4NO + 6H₂O (basic|main| process of HNO₃production)

Cl₂ and Br₂ oxidize ammonia vigorously:

2NH₃ + 3Cl₂ = N₂ + 6HCl

(this reaction proceeds also in solutions).

Ammonia interestingly|curiously| reacts with J₂.Thus forms extraordinarily unstable compound NI₃, which|what| |appear|, when it is dried up, violently explodes from| a least touch («chemical inviolability»).

NH₃ can reduce oxides|oxide|:

2NH₃ + 3CuO = 3Cu + N₂ + 3H₂O

On the whole|all in all| the properties|virtue| of NH₃ can be presented in such a chart:

Hydrazine, N₂H₄. It is a colourless toxic liquid which|what| easily evaporates (t_boiling = 113,5⁰С), it has high dielectric permeability ( = 52 at 25^оС), it is polar (=1.85 D).

The structure|building| of N₂H₄ is similar|like| to|by| H₂O₂ (the so-called|so called| goch-configuration|shape|):

Trans- goch-

More symmetric trans-form|shape| does not answer reality, as N₂H₄ has high dipole moment (1.85D), greater than in water, which|what| can not be demonstrated|shown,turned,displayed| at the symmetric trans form|shape|.

Preparation. In laboratory:

2NH₃ + NaClO = N₂H₄ + NaCl + H₂O

Chemical properties|virtue|. Chemical properties|virtue| of N₂H₄ look a great deal similar to those of ammonia. In its|its| aqueous|aquatic,water| solutions also exist hydrogen bonds|truss|. Basic|main| properties|virtue| of N₂H₄ are related|tied| to the mobility of electronic pair|couple| on the atom of nitrogen. Being a donor of two electronic pair|couple|, in an acidic medium|Wednesday| hydrazine adds protons:

NH₂NH₂ + H⁺ = NH₃⁺NH₂ К₁ = 8.5^.10^-7

NH₃⁺NH₂ + H⁺ = NH₃⁺NH₃⁺ К₂ = 8.5^.10^-15

As a result salts of |hydrazine are known as follows |that is why|:

N₂H₄ + HCl = [N₂H₅]Cl = N₂H₄^.HСl

N₂H₄ + 2HCl = [N₂H₆]²⁺Cl₂

Cation [N₂H₆]²⁺ is stable|firm| only at large|great,big| excess|overabundance| of strong acid, in other case it is|its| completely hydrolysed:

NH₃NH₃²⁺ + H₂O  NH₃NH₂⁺ + H₃O⁺

The atom of nitrogen in N₂H₄ is characterized|described| by Red-Ox duality:

demonstrates |virtue| reductive properties;

N₂H₄ + O₂ = N₂ + 2H₂O

3N₂H₄ = N₂ + 4NH₃

N₂H₄ + 2I₂ = N₂ + 4HI

N₂H₄ + 2Cl₂ = N₂ + 4HCl

5N₂H₄ + 4KMnO₄ + 6H₂SO₄ = 5N₂ + 4MnSO₄ + 2K₂SO₄ + 16H₂O

much weaker are expressed its oxidizing properties|virtue|

N₂H₄ + 2H⁺ = 2NH₃

(Zn+HCl)

Hydroxylamine, NH₂OH. It is a solid white compound, m.p. = 33 ^oС. Thermally unstable; at higher than 100^оС it explodes. Its|its| aqueous solutions are more stable|firm|.

Preparation. Electrolysis on cathode at reduction of HNO₃ solution by atomic hydrogen gives NH₂OH

HNO₃ + 6H⁺ + 6е = NH₂OH + 2H₂O

An atom of nitrogen in NH₂OH is a donor of electronic pair|couple|, that is why|that is why| NH₂OH forms a drogen bond. Like NH₃ and N₂H₄ in water of NH₂OH is a weak base|foundation|. In the series NH₃ (К = 10^-5)  N₂H₄ (К = 10^-6)  NH₂OH (К = 10^-8) basic|main| properties|virtue| diminish.

With acids NH₂OH forms salts according to reaction of addition type:

NH₂OH + HCl = [NH₃OH]Cl

Chemical properties|virtue| are similar to the properties|virtue| of NH₃ and N₂H₄.

NH₂OH is easily decomposed as a result of reaction of disproportioning|:

3NH₂OH = NH₃ + N₂ + 3H₂O

The atom of nitrogen in NH₂OH has an oxidation state (-1), that is why|that is why| it is simultaneously a reductant and oxidant.

Hydroxylamine demonstrates reductive properties|virtue|:

NH₂OH + K₂Cr₂O₇ + 4H₂SO₃ = 3N₂ + Cr₂(SO₄)₃ + K₂SO₄ + 13H₂O

2NH₂OH + I₂ + 2KOH = N₂ + 2KI + 4H₂O

4NH₂OH + O₂ = 2N₂ + 6H₂O

As well as oxidizing properties|virtue|:

2NH₂OH + 4FeSO₄ + 3H₂SO₄ = 2Fe₂(SO₄)₃ + (NH₄)₂SO₄ + 13H₂O

NH₂OH + 3HI = I₂ + NH₄I + H₂O

Hydrogen azide, HN₃. It is a colourless volatile|flying| liquid, t_boiling = 37⁰С, with a strong smell.

The least negative oxidation state of nitrogen (-1/3) is realised in HN₃ among the other hydrogen compounds|halving,compound,junction,joint,coupling| of nitrogen. This unusual oxidation state is determined by structural unequivalence of atoms of nitrogen. From a position of the Valence bond method | this unequivalence can be given by a chart:

The major point |head,leading| in this chart is delocalisation of | - bonds along the line which|what| connect the atoms of nitrogen. A correctness of the scheme is|proved,argued| confirmed by the value of distances between the atoms of nitrogen 1—2 and 2—3, which|what| are|appear| intermediate between the lengths of bonds -N=N- and NN. Atoms of nitrogen in the molecule of HN₃ are in the state|figure,camp,mill| of sp-hybridization, that is why|that is why| the ion of N₃^- has a linear structure.

Preparation. Water|aquatic| solution of HN₃ has name| hydroazoic| acid. It is prepared according to the reaction: N₂H₄ + HNO₂ = HN₃ + 2H₂O

Chemical properties|virtue|. It is weak acid (~ CH₃COOH)

HN₃ = H⁺ + N^-₃ К = 2^.10^-5

At heating of vapor|couple| of HN₃ higher to 300^оС it|it| is decomposed with an explosion|decomposed|:

2HN₃ = H₂ + 3N₂

In the waterless state|figure,camp,mill| HN₃ explodes even at shaking of a vessel, in the diluted state|figure,camp,mill| it is stable, as the reaction of its decomposition

HN₃ + H₂O = N₂ + NH₂OH (disproportioning|)

proceeds|leaves| extraordinarily slow|sluggishly|.

Reductive properties of HN₃ are not known|character,typical|, however there is a single reaction:

HN₃ + HNO₂ = N₂ + N₂O + H₂O

Oxidizing properties|virtue| of HN₃are characteristic|character,typical| (strong oxidant!!):

HN₃ + 3HCl = Cl₂ + N₂ + NH₄Cl

(N^.N₂)

The mixture of HN₃ with concentrated HСl dissolves|opens| Au and Pt, that similar aquafortis. According the oxidizing reactions HN₃ is similar to those of HNO₃ as a result of|because of,owing to| presence of four-covalent| nitrogen in their molecules:

Cu + 3HN₃ = Cu(N₃)₂ + NH₃ + N₂

Salts of HN₃ have name|called| azides|. An initial|output| product for the preparation of azides| is|appear| NaN₃, which|what| can be prepared|received|:

NaNH₂ + NO₂ = NaN₃ + H₂O

Azide| of lead Pb(N₃)₂ is used in detonators.

Phosphorus

Phosphorus compounds with H. Phosphorus practically does not react with H₂. The process:

2P + 3H₂  2PH₃ Н^о = -12.6 kJ / mol

p roceeds very slowly. At 350 ^oC and 200 atm PH₃ yield is close to 2% and the equilibrium under these conditions is established only in 6 days. Therefore, hydrogen compounds of phosphorus are usually obtained indirectly.

There are a few hydrogen compounds of P. The most studied is phosphine PH₃, and the so-called “liquid” P₂H₄ and “solid” P₄H₂ hydrogen phosphides.

Phosphine. This is a gas with a characteristic unpleasant smell. Pure phosphine is odourless, but technical grade phosphine has a highly unpleasant smell like garlic or rotten fish, due to the presence of substituted phosphine and diphosphine, P₂H₄. It is a very strong poison, which is a major obstacle to its practical application. Poisoning PH₃ damages nervous system. MAC PH₃ in air is 0.00001 mg / l.

Preparation. The most frequently used is the heating white P with concentrated aqueous solution of alkali:

Р₄ + 3NaОН + 3Н₂О = РН₃ + 3NаН₂РО₂