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General properties and structures of the elements

The first element nitrogen differs from the rest. Nitrogen is a colorless, odorless, tasteless gas, which is diamagnetic and exists as N2. The other elements are solids and exist as several allotropic forms. The N2 molecule contains a triple bond N ≡ N. This bond is very stable, and the dissociation energy is consequently very high. Thus, N2 is inert at room temperature, though it does react with Li, forming the nitride Li3N. Other isoelectronic species such as CO, CN, and NO+ are much more reactive than N2, and this is because the bonds are partly polar, while in N2 they are not.
The majority of compounds formed by this group are covalent. A coordination number of 4 is obtained if the lone pair is donated to another atom or ion. An example is the ammonium ion, Description: 51282.png.
It requires too much energy to remove all five outer electrons, so M5+ ions are not formed. However, Sb and Bi can lose just three electrons, forming M3+ ions, but the ionization energy is too high for the other elements to do so. Both SbF3 and BiF3 exist as ionic solids.
The M3+ ions are not very stable in solution. They can exist in fairly strong acid solutions but are rapidly hydrolyzed in water to give the antimony oxide ion (SbO+) or bismuth oxide ion (BiO+). This change is reversed by adding 5 M HCl.
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Strength of oxyacids of group VB elements

For an oxidation state of +5, the strengths of various acids of group 15 elements follow the order: HNO3 > H3PO4 > H3AsO4 > H3SbO4.
For the oxyacids involving the same element in different oxidation states, the strength of an acid depends on the number of unhydrogenated oxygen atoms attached to the central atom. For example, for the oxyacids of the type (OH)mZOn, the acid strength varies directly with the value of n. Thus, nitric acid (HNO3) is stronger than nitrous acid (HNO2).
The acids H3PO2, H3PO3, and H3PO4 are approximately of equal strength, because all these acids contain only one unhydrogenated oxygen atom each. The order of acid strength is H3PO2 > H3PO3 > H3PO4.

Oxides of nitrogen

Oxides of nitrogen provide a fascinating picture from the point of view of their varied structures and diverse chemical behavior. They range from N2O (oxidation state of nitrogen +1) through NO, N2O3, NO2, N2O4 to N2O5 in which the oxidation state of nitrogen is +5. Nitric oxide (NO) is colorless, neutral, and paramagnetic in which nitrogen has +2 oxidation states.
Structures: The structures of oxides of nitrogen differ from those formed by P, As, Sb, and Bi. The structures of nitrogen oxides are dictated by the tendency of nitrogen to form pπ–pπ multiple bonds. The structures of nitrogen oxides are given in the adjacent figure.
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Oxoacids of nitrogen

Oxidation state of N
Molecular formula
Hyponitrous acid
Description: 51311.png
2 (dibasic)
Very weak
Highly explosive
Nitrous acid
Description: 51318.png
1 (monobasic)
Unstable, weak acid
Nitric acid
Description: 51329.png
1 (monobasic)
Stable, strong acid


  1. Extraction of phosphorus: Phosphorus is obtained by heating bone ash or phosphorite rock [Ca3(PO4)2] with sand (SiO2) and coke (C) in an electric furnace at about 1770 K. The reactions are as follows:
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    Description: 51350.png
  2. Allotropes of phosphorus: Phosphorus exists in the five different allotropic forms: white, red, violet, black, and gaseous phosphorus. The most common of which are white and red solids. Solid violet and black allotropes are also known. Gaseous phosphorus exists as diphosphorus and atomic phosphorus.
    • White (yellow) phosphorus is extremely reactive.
    • Below 800°C, its vapor density corresponds to the formula P4. Above 1700°C, it exists as P2.
    • Due to its low ignition temperature (~30°C), it undergoes oxidation in the presence of air which slowly raises its temperature, and after a few moments it catches fire spontaneously. Due to this reason, it is stored in water.
      Description: 52267.png
Red phosphorus: Red phosphorus is stable allotrope at room temperature. Red phosphorus is formed by heating white phosphorus in the absence of air at about 250°C. It is not poisonous. It is safe to handle, because it does not burn spontaneously at room temperature.
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  • Ignition temperature of red phosphorus is high (~ 265°C).
  • It sublimes on heating. It melts at 610°C under pressure giving yellow liquid, which on cooling gives white phosphorus.
  • It is insoluble in carbon disulphide.
  • Red phosphorus has a polymeric structure.
  1. Oxides of phosphorous
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  2. Oxoacids of phosphorus: Phosphorus forms a large number of oxoacids. All these acids are based on tetrahedral four coordinated phosphorus atom containing at least one P = O unit and one P – OH group. Condensed systems are formed by P–O–P linkage or P–P linkage. Some of the common oxoacids of phosphorus are as follows:
Oxidation state of P
Molecular formula
Hypophosphorus acid
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Orthophosphorus acid
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Hypophosphoric acid
Description: 51391.png
Orthophosphoric acid
Description: 51402.png
Pyrophosphoric acid
Description: 51410.png
Metaphosphoric acid
Description: 52746.png

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