Phosphorus

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

2P + 3H₂  2PH₃ Н^о = -12.6 kJ / mol

proceeds 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.

P hosphine. 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

In addition:

Ca₃P₂ + 6HCl = 2РН₃ + 3 CaCl₂

Properties. Let us compare its physical properties with NH₃:

PH₃ molecule can be treated as an NH₃ analogue. Difference in the properties of PH₃ and NH₃ is associated with the following peculiarities of their structure:

• the length of bond N—H (0.1014 nm) is much shorter than the length of P—H bond (0.142 nm)

• NH₃ polarity (dipole moment is 1.47 D) significantly exceeds the polarity of PH₃ (0.55 D).

This is attributed to the absence of sp³-hybridization of valence orbitals in PH₃, which is typical of NH₃. Indeed, PH₃ molecule is pyramidal,  H-P-H = 93.5^o ( 90^o) (in NH₃ – 107.3^o). It indicates the decrease of contribution of s-orbital in the hybrid bonds of PH₃ formation, i.e. unshared electron pair of P is s-orbital (in case of NH₃ at the sp³-orbitals).

This PH₃ structure considerably complicates formation of donor-acceptor bonds with electron donors. Therefore, PH₃ has very weak basic properties.

The bond P—H is less strong (322 kJ / mol) than N—N (390 kJ / mol), PH₃ practically does not form H-bonds.

As, Sb, Bi Compounds E (-3)

The oxidation state –3 of these elements is found in arsenides, antimonides bismutides of s-elements of I and II groups. Metal-like compounds are formed in most of other cases (s-elements form salt-like compounds).

In the series of nitrides, phosphides, arsenides, antimonides, and bismutides of the same type gap width decreases, indicating an increase of contribution of delocalised bond (unlike covalent bonding that is localised along the bond axis of molecular structure compounds):

AlN AlP AlAs AlSb

 E, eV 3.8 3.0 2.16 1.6

Most of these compounds decompose under the action of acids.

HYDROGEN compounds.

As, Sb, Bi do not interact with hydrogen, so EH₃ is available only indirectly:

Mg₃Е₂ + 6HCl = 3MgCl₂ + 2H₃Е

or under the action of Zn on compounds of arsenic in acidic medium:

As₂O₃ + 6Zn + 12HCl = 2AsH₃ + 6ZnCl₂ + 3H₂O

This is known as the Marsh reaction (test for arcenic).

Arsine, AsH₃, stibine, SbH₃, bismuthine, BiH₃, are gases with a sharp smell. They, especially AsH₃, are one of the strongest inorganic poisons (generally, all volatile compounds and soluble compounds of arsenic are extremely poisonous). These compounds are also strongly endothermic, and therefore very unstable. Generally, in the series AsH₃—SbH₃—BiH₃ stability decreases. BiH₃ decomposes at the moment of liberation and its properties are not well studied.

	dE-H, nm	ЕЕ-Н, kJ/mol	Ноf, kJ/mol	НЕН	 ЕН3, D
NH3	0.101	390.4	-46.4	107.3o (sp3)	1.47
PH3	0.142	328.5	5.4	93.3 o ( - )	0.58
AsH3	0.152	279.2	66.5	92 o	0.22
SbH3	0.171	254.6	145	91 o	0.12
BiH3			230 (evaluation)

In the series of nonmetallic elements As—Sb—Bi is revealed the nonmetallicity weakening of EH₃ compounds. The structure of these molecules is similar to NH₃ and PH₃, (i.e., pyramidal structure with the atom of an element at the top and hydrogen atoms below). However, R_a is increased in the series N—P—As ... Bi and E-H polarity, the strength of bond is reduced; nonbonding orbital occupied by two electrons becomes less directed and the valence angle  HEH is decreased either.

The important property of EH₃ is their high reducing ability. For instance, arsine, AsH₃, can even reduce phosphorous acid H₃PO₃ to hypophosphorous H₃PO₂, although phosphorous acid itself is a very active reducing agent:

2 AsH₃ + 3 Н₃РО₃ = 3 Н₃РО₂ + 2 As + 3 Н₂О ( G^o = -60 kJ / mol)

EН₃ decomposes easily: 2EН₃ = 2E + 3H₂O

All hydrides EН₃ are dissolved well in water, but do not interact chemically. They burn in the air:

2EН₃ + 3О₂ = E₂О₃ + 3Н₂О

In the series NH₃—PH₃—AsH₃—SbH₃—BiH₃ donor properties of molecules are weakened, so the typical of NH₃ synthesis reaction is not observed in case of AsH₃ and SbH₃.

Properties of hydrides can be generalized as follows:

OXYGEN CONTAINING COMPOUNDS OF NITROGEN

Dinitrogen monoxide, N₂O. It is a gas colorless and any smell known as “exhilarant gas(laughing?!)”, as it has a narcotic action b.p. = -89⁰С, it is well dissolved in water: 0.6 volume in 1 volume of H₂O.

The chemical structure|building| of molecule of N₂O can be presented by the chart:

In accordance with sp-hybridization the molecule of N₂O has a linear structure|building|:

N^-=N⁺=O  NN⁺—O^-  N^-=N⁺—O^-

Preparation. In laboratory:

1. Thermal decomposition of ammonium nitrate (or hydroxylamine nitrite|):

2. Weak heating of sulfaminic| acid with HNO₃:

HNO₃ + NH₂SO₂OH = N₂O + H₂SO₄ + H₂O

By chemical properties N₂O is a nonsaltforming oxide.

At the weak heating it is decomposed:

2N₂O = 2N₂ + O₂

that is why|that is why| N₂O is a strong oxidant:

N₂O + H₂ = N₂ + H₂O

3N₂O + 2NH₃ = 4N₂ + 3H₂O

N₂O + H₂SO₃ = N₂ + H₂SO₄

Cu + N₂O = N₂ + CuO

N₂O does not interact with water, thou hyponitrous, | acid H₂N₂O₂, in which|what| nitrogen has an oxidation state (+1) is known. Its structure has two equivalent atoms of nitrogen.

Free H₂N₂O₂ is isolated|receive|:

It|it| is well dissolved in water, but as an acid it is very weak (К₁ = 10^-8, К₂ = 10^-12). H₂N₂O₂ is very unstable, at even slight heating it explodes:

H₂N₂O₂ = N₂O + H₂O

Nitrogen mooxide, NO. It is a gas without color and smell (b.p. = -152 ^oС), not soluble in water. A candle does not burn|burning| in NO, red phosphorus however burns|burning| [explanation - like burning of magnesium in N₂].

In nature it forms at thunderstorm discharges|discharge,rank|:

O₂ + hv O^o + O^o;

O^o + N₂  NO + N^o;

N^o + O₂  NO + O^o and others

NO is unique|single,sole,only,common| compound as it is the only oxide of nitrogen which|what| can be prepared|received| by direct|immediate| interaction of elements.

Preparation. In a laboratory:

3Cu + 8HNO_3(dilut) = 2NO + 3Cu(NO₃)₂ + 4H₂O

In industry:

4NH₃ + 5O₂ = 4NO + 6H₂O

Properties|virtue|. For nitrogen mathematically even oxidation states (+2, +4) are comparatively little characteristic|character,typical|. NO belongs|behave| to|by| the number of such compounds|halving,compound,junction,joint,coupling|. The molecule of NO is paramagnetic, that is deduced out of МО method|. The molecule of NO contains|maintain| the odd number of electrons. Compared with N₂ molecule (according to МО| method N₂ [KK 2s²^*2s²2p²_y2p²_z2p²_x]) an additional electron is contained|maintained| on antibonding orbitals|, that is why|that is why| the order of bond in the molecule of NO (according the method of МО| NO[KK 2s²^*2s²2p²_y2p_z2p²_x^*2p_y])is equal 2,5:

.

For this reason the molecule of NO is not decomposed back to the elements, although it|it| endothermic and has a positive|staid| G of formation|formation| from elements.

Without regard to|in spite of,regardless of| the enormous amount|quantity| of researches, devoted to the structure|building| of NO, it is still an «enigmatic» molecule: it|it| is|appear| odd numbered, as it contains|maintain| 11 valency electrons, but it is little inclined|liable,predisposed,located| to|by| dimerization|. Only at low temperatures it|it| is dimerized| onto (NO)₂ - a compound of dark blue color, but not completly (even at -163^оС only at 95%), and only the solid NO is dimerized| by 100%. Other properties|virtue| of NO are also unusual: through|from,because of| a unpaired| electron it is paramagnetic, but this compound is for some reason uncolorless as compared to other even molecules it is sufficiently|enough| stable (thermally) and relatively|in relation to| low reactive|clever|.

NO is a paramagnetic molecule, that is why|that is why| tries|attempt,endeavour| to give|return| or to add an electron:

1) NO -e^-  NO⁺ -9,3 В nitrosyl|

This ion it forms on such conditions:

N₂O₃ + 3H₂SO₄ = 2NO⁺ + 3HSO₄^- + H₃O⁺

Nitrosonium| hydogen sulfate, NO⁺HSO₄^- (nitrosylsulfuric| acid) is an intermediate| in the tower method of preparation of H₂SO₄. Other salts of nitrosonium are known: NO⁺ClO₄^- NO⁺BF₄^-. Salts of nitrosonium |are| easily hydrolysed:

NO⁺ + H₂O = H⁺ + HNO₂

2) NO + e^-  NO^-

Such salts are formed at interaction of Na and NO in liquid|rare,thin| ammonia:

Na + NO Na + NO^-