Group 15 Elements: Nitrogen Family | Inorganic Chemistry PDF Download

GROUP 15^TH ELEMENTS (NITROGEN FAMILY)

NITROGEN

Preparation

1. NH₄NO₂ N₂↑+ 4H₂O + Cr₂O₃

2. (NH₄)2Cr₂O₇   N₂↑ + 4H₂O + Cr₂O₃

3. 8NH₃ + 3Cl₂  6NH₄Cl + N₂

Properties

(1) N₂ is a colourless odourless gas insoluble in water.

(2) It is absorbed by heating with Mg and Al. The nitrides formed thus react with water to form NH₃.

3Mg + N₂→Mg₃N₂ (+6H₂O)→3Mg(OH)₃ + 2NH₃↑

2Al + N₂→2AlN (+6H₂O)→2Al(OH)₃ + 2NH₃↑

(3) Reaction with H₂ at 200 atm and 500 °C and in the presence of iron catalyst and molybdenum promotes N₂ combination with H₂ reversibly to form ammonia. The process in called Haber’s Process and is the industrial method of manufacturing ammonia. The reaction is exothermic. 

(4) Reaction with oxygen: When air free from CO₂ and moisture is passed over an electric are at 2000-3000°C nitric oxide is formed. This reaction its endothermic.

N2 + O2 → 2NO

AMMONIA (NH₃)

Preparation:

1. NH₄Cl + NaOH  NH₃ ↑ ­+ NaCl + H₂O

2. (NH₄)₂SO₄ + 2NaOH  2NH₃ ↑ ­+ Na₂SO₄ + 2H₂O

3. NH₄NO₃ + NaOH  NH₃ ­↑ + NaNO₃ + H₂O

Haber’s process: N₂ + 3H₂

Cyanamide Process

(i) CaO + 2C + N₂ CaCN₂ + CO ↑

(ii) CaCN₂ + 3H₂O → CaCO₃ + 2NH₃ ↑ ­

Properties

1. Na + NH3  NaNH₂ + 1/2H₂

2. 4NH₃ + 5O₂ 4NO + 6H₂O

3. CuSO₄ + 2NH₄OH  Cu(OH)₂ ↓ (blue) + (NH₄)2SO₄

4. Cu(OH)₂ + (NH₄)₂SO₄ + 3NH₄OH (excess)  [Cu(NH₃)₄]SO₄ (deep blue solution) + 4H₂O

OXIDES OF NITROGEN

Oxides of nitrogen	Structure	Physical state	Colour of gas
N2O		Gas	Colurless
NO		Gas	Colourless
N2O3			Blue liquid (–30°C)
NO2		Gas	Brown
N2O5		Colourless solid	–(no existence in gas phase)

Preparation:

1. NH₄NO₃ N₂O + 2H₂O

2. 3Cu + 8HNO₃ → 3Cu(NO₃)₂ + 2NO + 4H₂O

Properties

1. Oxides of nitrogen are all oxidizing a gents.

2. (a) N₂O is isoelectronic with CO₂ and also has linear structure. However, unlike CO ₂, N₂O has a small dipole moment.

(b) No has total of 15 electrons. This is an odd electron molecule. In the gaseous state, it is paramagnetic. However the liquid and the solid states are diamagnetic because lose dimmers are formed canceling out the magnetic effects of unpaired electrons.

The bonding in NO is best described by the molecular orbital theory. Its electronic configuration is

This gives a bound order of 2.5. If the u npaired electron occu pying he a nti bonding π*2p_y orbital is removed, nitrosonium ion NO⁺ is formed and bond order becomes 3. This is reflected in the thortning of the bond length from 115 pm in NO to 106 pm in NO⁺. Nitrosonium ion is stable and forms salts like NO⁺Cl^-. It is isoelectronic with CO and forms complexes with transition elements. The brown ring formed in the test for nitrates is due to the formation of a complex of iron [Fe(H₂O)₅NO]²⁺

(c) NO₂ with 23 electrons is aga in an odd electron molecule. In the gaseou s state it is para magnetic. On cooling, the gas condenses to a brown liquid and eventually to a colourless solid both of which are diamagnetic due to dimerisation. NO₂ molecule is angular with ONO angle of 134°. The O —N bond length is 120 pm. Intermediate between a single and double bond. The odd electron is o nitrogen. The dimer has been shown to have a linear structure. The N—N bond length is very large 174 cm making this a very weak bond liquid N₂O₄ undergoes self-ionizatin to form NO⁺ and NO₃^– ions and (therefore it has been extensively studied as a non-aqueous solvent

(d) Solid N₂O₅ exists in the ionic form NO₂⁺ NO₃^– in the gaseous form, the discreate N₂O₅ molecules have a N—O—N bond angle close to 112°

Properties:

N₂O: (a) Reduction: Cu(hot) + N₂O → CuO + N₂

(b) Oxidation: 2KMnO₄ + 2H₂SO₄ → K₂SO₄ + 2MnSO₄ + 3H₂O + 10NO

NO: (a) Oxidizing properties (Reduction of NO)

(b) Reducing properties (oxidation of NO):

6KMnO₄ + 9H₂SO₄ + 10 NO → 3K₂SO₄ + 6MnSO₄ + 4H₂O + 10HNO₃

NO₂: It behaves both like HNO₂ as a reducing agent and like HNO₃ as an oxidizing agent according to following reactions respectively.

2KMnO₄ + 3H₂SO₄ + 10NO₂ + 2H₂O → K₂SO₄ + 2MnSO₄ + 10HNO₃

SO₂ + H₂O + NO₂  → H₂SO₄ + NO

OXYACIDS OF NITROGEN

NITROUS ACID (HNO₂)

Preparation

1. Ba(NO₃) + H₂SO₄ → 2HNO₂ + BaSO₄↓

Properties

(i) Nitrous acid and nitrites are good oxidizing agents and covert iodides to iodine, ferrous salts to ferric stannous to stannic and sulphites to sulphates eg.

2KI + 2HNO₂ + 2HCl  → 2H₂O + 2NO + 2KCl + I₂

(ii) With strong oxidizing a gents like KMnO₄, nitrou s a cid a nd nitrites function a s redu cing agents a nd get oxidized to NO₃^– ions

2KMnO₄ + 5KNO₂ + 6HCl → 2MnCl₂ + 5KNO₃ + 3H₂O + 2KCl

NITRIC ACID (HNO₃)

Preparation

HNO₃ is exclu sively manu factured by the Ostwald process. In this process NH₃ is catalystically oxidized to NO over a Pt—Rh catalyst at 1200 K

  ΔH = -904 Kj

The mixture is then diluted with air NO combine s with O₂ to give NO₂ which is absorbed in water to give HNO₃ and NO which is then recycled.

(ii) 2NO + O₂ → 2NO₂

(iii) 3NO₂ + H₂O → 2HNO₃ + NO

Properties

(i) Thermal stability

(ii) Oxidizing Properties:

(a) H₂S + 2HNO₃ (conc.)→2H₂O + 2NO₂ + S ↓

(b) 3H₂O + 2HNO₃ (dilute) → 4H₂O + 2NO + 3S 

(c) SO2 + 2HNO₃ (conc.) → H₂SO₄ + 2NO₂ ­ 

(d) 3SO₂ + 2H₂O + 2HNO₃ (dilute)→ 3H₂SO₄ + 2NO 

(e) Zn + 4HNO₃(conc.) →Zn(NO₃)₂ + 2H2O + 2NO₂ 

(f) 4Zn + 10HNO₃(dil.) → 4Zn(NO₃)₂ + 5H₂O + N₂O 

(g) Cu + 4HNO₃(conc.) → Cu(NO₃)₂ + 2NO₂ + 2H₂O 

(h) 3Cu + 8HNO₃ (v. dil) → 3Cu(NO₃)₂ + NO + 4H₂O

PHOSPHORUOUS (P)

It is a very reactive non-metal. It catches fire in air. It occurs in nature in the form of stable phosphates. The important minerals are:

(i) Phosphorite, Ca₃(PO₄)₂ 

(ii) Vivianite, Fe₃(PO₄)₂8H₂O

EXTRACTION

Ca₃(PO₄)₂ + 2SiO₂ 3CaSiO₃ + P₂O₅

P₂O₅ + 5C 2P↑ ­ + 5CO↑­

ALLOTROPIC FORMS OF PHOSPHOROUS 

(i) WHITE OR YELLOW PHOSPHORUS (P₄)

Properties

(1) It is white-too-transparent and soft waxy solid 

(2) It is soluble in CS₂ but insoluble in water. 

(3) It glows in dark due to slow oxidation producing yellowish-green light. This phenomenon is called phosphorescence. 

(4) White phosphrous is poisonous. 

(5) It runs yellow after some time, it is called yellow phosphorus. 

(6) It undergoes oxidation in the presence of air which slowly rises its temperature and due to its low ignition temperature (30°C) after a few moments it catches fire spontaneously. Due to this reason it is stored under water.

(ii) RED PHOSPHORUS 

Preparation

When white phosphorus is heated in the atomosphere of CO₂ or coal gas at 250°C red phosphorus is produced. This red phosphorus may still contain some white phosphorus which is removed by boiling the mixture with NaOH where white phosphorus is converted into PH₃ gas but red phosphorus remains inert.

It is also prepared by heating white phosphorus with a few crystals of iodine catalyst at 250°C under high pressure.

Properties

It is red crystalline solid having a density of 2.2 g/cc. It is less reactive then white phosphorus and does not dissolve in liquid CS₂. It does not catch fire at room temperature because its ignition temperature is 260°C. It is a polymeric substance forming linear chains like this.

(iii) BLACK PHOSPHOROUS

Preparation

When white phosphorus is heated at about 200°C under very high pressure then black phosphorous is produced.

Properties

It is an electrical conductor resembling graphite in this respect and also in its flakiness and luster. It is often called metallic phosphorous. Its density (2.69 g/cc) is higher than of red phosphorous. It is insoluble in CS₂. It has layered structure like graphite.

(iv) BROWN PHOSPHOROUS 

Above 1600°C P₄ molecules break into P₂ molecules. Rapid cooling of this vapour gives brown phosphorus which probably contains P₂ molecules.

(v) SCARLET PBHOSPHROUS

This allotrope is obtained in the form of an amorphous scarlet powder by boiling a 10 percent solution of phosphorus in phosphorus tribromide for about 10 hours. Pure scarlet phosphorus may be prepared by heating  phosphorus tribromide with mercury at 240°C.

Scarlet phosphorus

Scarlet phosphorus resembles the red variety in its physical properties and the white phosphorus in its chemical properties. It is, however, only slowly oxidized in air.

(iv) VIOLET PHOSPHORUS

This variety is obtained by heating white phosphorus with a trace of sodium at 230°C under high pressure. It is crystalline in structure.

CHEMICAL PROEPERTIES OF PHOSPHORUS

Reactivity of the various allotropic forms of phosphorus towards other substances decreases in the order.

Brown > white > red > black, the last one being almost inert & thermodynamically most stable form of phosphorus.

(i) Action of air: White phosphorus burns in air to form phosphorus trioxide and pentoxide. 

Red and other forms of phosphorus also burn in air or oxygen but on heating.

(ii) Halide: Nitrogen is unable to form pentahalides because the second shell contains a maximum of eight electrons, i.e., four bonds. The subsequent elements have suitable d orbitals and form the following pentahalides PX₅.

PCl₅ + 4H₂O→H₃PO₄ + 5HCl

Despite the existence of pentahalides no hydrides MH₅ are k nown. To attain the five valent state, d orbitals must be used. Hydrogen is not sufficiently electronegative to make the d orbitals contract sufficiently, through PHF₄ and PH₂F₃ have been isolated.

(iii) Action with Non metals: When heated with non-metals phosphorous forms compounds PX₃, PX₅, P₂S₃ and P₂S₅

2P + 3X₂→2PX₃,

2P + 5X₂→2PX₅. (where X = Cl, Br and I)

(iv) Action with metals: Alkali metals when heated with white phosphorus in vacuum produce alkali metal phosphide, which react with water to form phosphine gas.

3M + P  M₃P

M₃P + 3H₂O3MOH + PH₃ ↑­ (where M = Na, K etc.)

(v) Action of NaOH: When white phosphorus is heated with NaOH solution, phosphine gas is evolved.

P₄ + 5HNO₃ →3NaH₂PO₂ + PH₃ ­↑

(vi) Action of conc. HNO₃/H₂SO₄: When heated with conc. HNO₃ phosphorous is oxidized to H₃PO₄.

P + 5HNO₃→H₃PO₄ + 5NO₂ ↑ + H₂O

PHOSPHORUS TRIOXIDE (P₂O₃)

It is prepared by burning phosphorus in a limited supply of oxygen when gaseous P₄O₁₀ and P₄O₆ are formed.

Properties

(i) It is colourless crystalline solid having mp 23.8 °C and bp 178 °C.

 (ii) It dissolves in cold water to form phosphorous acid, it is thus the anhydride of phosphorous acid. 

P₂O3 + 3H₂O → 2H₃PO₃

(iii) It burns in Cl₂ gas forming phosphorous oxytricholoride (POCl ₃) and phosphoryl chloride (PO₂Cl) 

P₂O₃ + 2Cl₂ →POCl₃ + PO₂Cl

PHOSPHOROUS PENTOXIDE (P₂O₅)

Preparation

It is obtained by burning phosphorous in air.

P₄ + 5O₂ →P₄O₁₀

Properties

(i) It is a white powder acidic in nature and is the anhydride of orthophosphoric acid. Its empirical formula is P₂O₅ and its molecular formula is P₄O₁₀. 

(ii) Action of water: It dehydrates in water with hissing sound forming metaphospharic acid and finally orthophosphoric acid

P₄O₁₀ + 2H₂O→4HPO₃;

HPO₃ + H₂O →H₃PO₄

(iii) Dehydrating power: It dehydrates conc. H₂SO₄ and cocnc. HNO₃ to SO₃ and N₂O₅ respectively.

OXY-ACID OF PHOSPHOROUS

PHOSPHOROUS ACID (H₃PO₃)

Preparation

(i) By dissolving P₂O₃ in water

P₂O₃ + 3H₂O→2H₃PO₃

(ii) By hydrolysis of PCl₃ with water.

PCl₃ + 3H₂O → H₃PO₃ + 3HCl

Properties

(i) It is a white crystalline solid soluble in water and having melting point of 74°C 

(ii) It is a weak acid and reducing a gent. 

(iii) 4H₃PO₃ 3H₃PO₄ + PH₃ (Disproportionation) 

(iv) H₃PO₃ + 3PCl₃ → PCl₃ + 3POCl₃ + 3HCl 

(v) It is a strong reducing agent 

2AgNO₃ + H₃PO₃ + H₂O → 2Ag + 2HNO₃ + H₃PO₄

ORTHOPHORSPHORIC ACID (H₃PO₄)

Preparation

(i) Ca₃(PO₄)₂ + 3H₂SO₄→2H₃PO₄ + 3CaSO₄

(ii) P₄O₁₀ + 6H₂O→4H₃PO₄

(iii) P₄ + 20HNO₃ →4H₃PO₄ + 20NO₂ + 4H₂O

Properties 

Reacting of H₃PO₄: The simplest phosphorous acid is H₃PO₄ (orthophosphoric acid). The acid contains three replaceable H atoms and is tribasic.

(i) Pure orthophosphoric acid is a white crystalline solid highly soluble in water having melting point of 42°C. It is a weak acid. It forms two acid salts and one normal salt. NaH₂PO₄ is sodiu m dihydrogen phosphate, Na₂HPO₄ is disodium hydrogen phosphate & Na₃PO₄ is sodium orthophosphate.

(ii) Action of Heat:

(iii) Neutralization with alkalis or bases:

Polyphosphonitrilic chlorides (PNCl₂) (n = 3 to 7)

These polymers are also called inorganic rubbers. These compounds are can be represented by the General structure,

Preparation:

(i) (NPCl)₃ and (NPCl₂)₄ can be prepared by the ammonolysis of PCl₅.

3PCl₅ + 3NH₃→(NPCl₂)₃ + 9HCl 

4PCl₅ + 4NH₃ → (NPCl₂)₄ + 12HCl

(ii) These compou nds can be prepared by the reaction between PCl₅ and NH₄Cl in presence of C₂H₄Cl₂ or C₆H₅Cl or by heating PCl₅ with solid NH₄CH at 145-160°C

nPCl₅ + nNH₄Cl (NPCl₂)_n + 4HCl

nPCl₅ + nNH₄Cl(s) (NPCl₂)_n + 4nHCl

Properties: 

Reactions involving replacement of Cl-atom of P—Cl bond:

(i) (NPCl₂)₃ + 6NaF  (NPF₂)₃ + 6NaCl

(ii) [NPCl₂)₃ + 2NaOCH₃ [ NP(OCH₃ )₂ ] 2NaCl Tri(dimethoxy) phosphazine

(iii) [NPCl₂)₃ + 6C₆H₅MgBr   [NP(C₆H₅)₂]₃ + 3MgCl₂ + 3MgBr₂

(iv)

Or

Hydrolysis:

Reaction with benzene, C₆H₆ (Friedel-Crafts reaction):

N3P3Cl₆ + 2C₆H₆  N₃P₃Cl₄ (C₆H₅)₂ + 2HCl

PbF₂ fluorinates N₃P₃Cl₆ (trimer) giving ultimately N₃P₃F₆.

N₃P₃Cl₆ + 3PbF₂ →N₃P₃F₆ + 3PbCl₂

Structure of (NPCl₂)₃ molecule: X-ray analysis has shown that (NPCl₂) molecule has a planar sixmembered ring structure (Structural) in which each N -atom is sp² hybridized and each P-atom is sp³ hybridized. The lone pair of electrons on each N -atom resides in one of the three sp² hybrid orbitals. It is this lone pair of electrons which makes (NPCl₂)₃ molecule to show basic properties. The bond angles are as shown in the structure. Resonance structure can also be drawn as in case of C₆H₆ molecule, indicating aromaticity in the ring.

Unlike benzene which involves extensive (pπ- pπ) bonding. (N₃P₃Cl₆) molecule involves (dπ-pπ) bonding. The extent (dπ-pπ) bonding appears to be quite appreciable as the N—P distance (1.6 Å) is considerably shorter than the N—P single bond distance (1.75-7.80 Å). Whether there is complete delocalization of π-electron charge cloud on all the ring a to ms as in C₆H₆ molecule or there are intensely-localized islands of the electron cloud within the PNP segments cannot be answered with certainity.

Structure of (NPCl₂)₄ molecule: This molecule has a tube-like puckered structure.

Borophosphate glasses

These are formed by heating H₃PO_4, B₂O₃ and alkali metal carbonates or oxides at 700 °C. Borophosphate glasses are of the following three types. (i) Those which contain excess of alkali over P₂O₅ in this variety all the B atoms are present a s trigonal BO₃ groups.

(ii) Those which contain excess of P₂O₅ over alkali. These borophosphate glasses are called acidic borophosphate glasses. If there is less than 10 mole percent of B₂O₃ all B-atoms are four coordinated.

(iii) Those which contain P₂O₅ and alkali in equivalent proportions. The number of coordinated B -atoms decreases steadily with the increase in the content of B₂O₃ and becomes almost zero at about 47 mole per cent of B₂O₃.

Structure of borophosphate glass having three and four coordinate B atoms are shown below in following figure.