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Carbon differs from rest of the members of its group due to its smaller size, higher electro negativity, higher ionization enthalpy and unavailability of d-orbital’s.

In carbon, only s and p orbital’s are available for bonding and therefore it can accommodate only four pairs of electrons around it. This limit the maximum covalence to four whereas other members can expand their covalence due to the presence of d-orbital’s.

Due to property of catenation and pπ - pπ bond formation Carbon is able to show different allotropic forms.

Carbon has the unique ability to form pπ – pπ multiple bond with itself and with other atoms of small size and high electro negativity whereas heavier elements do not from pπ – pπ bonds because their atomic orbital’s are too large and diffuse to have effective overlapping.

Mixture of CO and N₂

2B + 6NaOH → 2Na₃BO₃ + 3H₂

Nitrogen exists as a diatomic molecule (N = N). Due to the presence of a triple bond between the two nitrogen atoms the bond dissociation energy is quite large (941.1 kJ mol^-1). As a result, nitrogen is inert and unreactive in its elemental state.

In contrast phosphorus exists as a tetraatomic molecule (P₄). Since the P-P single bond is much weaker (213 kJ mol^-1) than N = N bond. Therefore, phosphorus is much reactive than nitrogen.

BF₃ < BCl₃ < BBr₃ <BI₃.

The non-metals and the metalloids exist only in the p-block of the periodic table. The non-metallic character of elements decreases down the group. In fact the heaviest element in each p-black group is the most metallic in nature.

General trends in chemical properties of group-15

(i) Reactivity towards hydrogen:
The elements of group 15 react with hydrogen to form hydrides of type EH₃, where E - N, P, As, Sb, or Bi. The stability of hydrides decreases on moving down from NH₃ to BiH₃

(ii) Reactivity towards oxygen:
The elements of group 15 form two types of oxides: E₂O₃ arid E₂O₅, where E = N, P, As, Sb or Bi. The oxide with the element in higher oxidation state is more acidic than the other. However, the acidic character decreases on moving down a group.

(iii) Reactivity towards halogens:
The group 15 element react with halogens to form two series of salts: EX₃ and EX₅. However, nitrogen does not form NX₅ as H lacks the d-orbital. All trihalides (except NX₃) are stable.

(iv) Reactivity towards metals:
The group 15 elements react with metals to form binary compounds in which these metals exhibit-3 oxidation states.

Carbon and silicon are non metals. Germanium is a metalloid and tin and lead are metals. Metallic character increases from carbon to lead. The change from non metallic to metallic character is due to the increase in atomic size from carbon to lead. Consequently the ionization potential decreases from carbon to lead.

Hence the electropositive character increases favouring ionic bonding especially with oxidation state +2. Whereas carbon and silicon show +4 oxidation state forming covalent bonding with electron sharing.

1. Small size of carbon atoms. 

2. C-C bond energy is comparable with the bond energy between carbon and other element 

3. 4 valency electrons are present in four orbitals and the tetravalency of carbon is fully saturated.

A mixture of dilute NaOH and aluminum pieces is used to open drain.

Sodium hydroxide and aluminum react to form sodium tetra hydroxy aluminate(III) and hydrogen gas. The pressure of the produced hydrogen gas is used to open blocked drains.

2Al+2NaOH+6H₂O→2Na+[Al(OH)₄]⁻+3H₂

N (unlike p) lacks d-orbital. This restricts nitrogen to expand its coordination number beyond four. Hence, R₃N = O doesnot exits.

The state of hybridization of carbon in:

(a) Graphite -- Each carbon atom in graphite is sp² hybridized and is bound to 3 other carbon atoms. 

(b) CO²⁻₃ - C is sp² hybridized and is bonded to 3 oxygen atoms. 

(c) Diamond -- Each carbon in diamond is sp³ hybridized and is bound to 4 other carbon atoms.

In diamond sp³, in graphite sp².

No free electrons in diamond due to sp³ hybridization. But there are free electrons in graphite due to sp² hybridization. 

The chemical formula of pyrophosphorous acid H₄P₂O₅.

Good conductor of electricity: In. graphite carbon atom is sp² hybridised. Out of four valancy electrons in each carbon atom only three electrons, one from 2s and two from 2p are involved in hybridisation. One spare electron in its 2p_z orbital is left free. These 2p_z orbital overlap to form delocalised π system which extends above and below each layer. In this delocalised π electrons are free to move within the layer and hence graphite is a good conductor of electricity.

The conductivity of graphite perpendicular to the plane of the layers of hexagons is low and increases with increase in temperature, signifying that graphite is a semiconductor in that direction. The electrical conductivity is much higher parallel to the plane but decreases as the temperature is raised.

Soft, flaky and slippery substance: In graphite each layers of hexagon are held together by a weak Van der Waal’s force of attraction at a large distance of 3.40 Å. Even the slight pressure causes the layers to slide over one another. Hence graphite is soft, flaky and slippery. Graphite is used as a lubricant.

The formula of inorganic benzene is B₃N₃H₆.

Borazine-  B₃N₃H₆

BH₃ exists in form of diborane (B₄H₆) because it is electron deficient. Diborane is used as reducing agent.

C₆₀ dissolves in hydrocarbon solvents such as hexane, benzene, toluene etc giving magenta solutions. Fullerenes are the least stable of the carbon allotropes and graphite is the most stable. Fullerenes react with alkali metals to produce solids having composition such as K₃ C₆₀. This compound acts as a superconductor below 18K. Fullerene C₁₁₄ has more surface area and can withstand a very high temperature. Hence it can be used as a lubricant in satellites. Fullerenes are used as industrial catalyst and as lubricant in the treatment of cancer.

1. Colourless fuming liquid.
2. Melting point is 231.4k.
3. Boiling point is 355.6k.

The structural unit of silicates is SiO₄^4- in which silicon atom is bonded to four oxygen atoms in tetrahedron fashion.

Boron, carbon, Nitrogen

Boron:

(i) W, forms acuhc. oxides -whereas owners item. am-phofork and.bask, oxide. 

(ii) It cannot form [BFe]³⁺ whereas others can form such type of complexes.

Carbon: 

(i) It shows property of catenation to maximum extent. 

Nitrogen:

(i) N₂ is gas others are solid 

(ii) NH₂ is liquid, other hydrides are gases.

Since the O.N. of C is CO₂ is +4 which is the maximum for C, therefore, it cannot act as a reducing agent. In contrast the O.N. of S is SO₂ is also +4 but its maximum. O.N. +6, therefore, it can act as reducing agent. This reducing gas can be removed by passing the mixture of these gases through acidified K₂Cr₂O₇ solution when orange solution turns green due to reduction of Cr₂O₇^2- ion to Cr³⁺ ions while CO₂ passes out unreacted.

(i) Nitric oxide becomes brown when released in air because Nitric oxide combines with oxygen when exposed to air to give nitrogen dioxide which is brown in colour.

2NO + O₂ ⟶ 2NO₂​ 

(ii) Bi has little tendency to form pentahalides because + 5 oxidation state of Bi is much less stable than + 3 oxidation state due to inert pair effect.

The electronic configuration of boron is ns² np¹. It contains 3 electrons in its valence shell. Thus, it can form only 3 covalent bonds which means that there are only 6 electrons around boron and its octet remains incomplete. When 1 of the boron‘s atom combines with 3 fluorine atoms, its octet (8) remains incomplete. Therefore, boron trifluoride remains electron-deficient and acts as Lewis acid.

(i) CaCO₃ + 2HCl → CaCl₂ + CO₂ + H₂O 

(ii) Na₂CO₃ + 2H₂O → 2NaOH + H₂CO₃ 

(iii) CaC₂(calcium carbide) + 2H₂O → Ca(OH)₂ + C₂H₂(Acetylene)

Solid CO₂ is known as dry ice.

Ni has oxidation state of zero in [Ni(CO)₄]

The highly poisonous nature of CO arises because of its ability to form a complex with haemoglobin which is about 300 times more stable than the oxygen – haemoglobin complex. This prevents haemoglobin in the red blood corpuscles from carrying oxygen round the body and ultimately resulting in death.

As a result of the difference in the electronegativities of Cl and B, the B–Cl bond is naturally polar. However, the BCl₃ molecule is non-polar. This is because BCl₃ is trigonal planar in shape. It is a symmetrical molecule. Hence, the respective dipole moments of the B–Cl bond cancel each other, thereby causing a zero dipole moment.

Carbon monoxide is highly poisonous due to its ability to form a complex with hemoglobin. The former prevents Hb from binding with oxygen. Thus, a person dies because of suffocation on not receiving oxygen The CO–Hb complexly is more stable than the O₂–Hb complex. It is found that the CO–Hb complex is about 300 times more stable than the O₂–Hb complex.

Hydrogen fluoride is a covalent compound and has a very strong intermolecular hydrogen-bonding. Thus, it does not provide ions and aluminum fluoride does not dissolve in it. Sodium fluoride is an ionic compound and when it is added to the mixture, Alf dissolves. This is because of the availability of free F^– . The reaction involved in the process is:

AlF₃+3NaF→Na₃[AlF₆]

Aluminum fluoride gets precipitated out of the solution when boron trifluoride is added to the solution. This happens because the tendency of boron to form complexes is much more than that of aluminum. Therefore, when boron trifluoride is added to the solution, B replaces Al from the complexes according to the following reaction:

Na₃[AlF₆]+3BF₃→3Na[BF₄]+AlF₃

AlF₃ is more ionic, therefore, has higher melting point.

Silica gel is used as a drying agent and as a support for chromato graphic materials and catalysts.

Due to extra stable of half filled p orbital configuration present in 15 group element. 

PH₃ react with acid like HI to give PH₄

Due to absence of d orbital it does not form pentahalide. But due to involvement of s and p orbit it exhibits +5 oxidation state.

NO₂ contain odd number of valence electron. On dimirisation it gives a stable N₂O₄ molecule.

Because of hydrogen bond which is present in NH₃.

Noble gases do not form molecules. In case of noble gases. the atomic radii corresponds to Van der Waals radii. On the other hand, the atomic radii of other elements correspond to their covalent radii. By definition, Van der WaaI’s radii are larger than covalent radii. It is for this reason that noble gases are very large in size as compared to other atoms belonging to the same period.

General characteristic of group-15 elements:

(A) Electronic configurations :
The atoms of group 15 have five electrons in the outermost shell, two in s and three in p subshell. The general electronic configuration of this group may be expressed as ns² np³

(B) Oxidation state :
The elements of group-15 have five electrons in their valence shell. They exhibit various oxidation states from -3 to +5.

(i) The tendancy of the elements to exhibit – 3 oxidation state decreases on moving down from P to Bi due to increase in size and metallic character.

(ii) On moving down the group, the stability of + 5 oxidatioin state decreases while that of + 3 oxidation state increases due to inert pair effect.

(C) Atomic size:
The atomic and ionic radii of group-15 elements are smaller than the atomic radii of the elements of group 14 elements. On going down the group, the atomic radii increase with increase in atomic number.
Order of Atomic size :
N > P> As > Sb > Bi

(D) Electronegativity :
The electrogativity values of elements of group-15 are higher than the corresponding elements of group-14. On going down the group, the electronegativity value decrease.
Order of electronegativity given as :
N   > P >  As > Sb > Bi
(3.0) (2.1) (2.0) (1.9)  (1.9)

(A) Uses of Neon gas:

1. It is used in safety devices for protecting electrical instruments like voltmeters, relays, ractifires etc.

2. Neon is used for filling sodium vapour lamps.

3. It is used in Beacon light as safety signal for air navigators, because its light has high penetration power.

(B) Uses of Argon gas:

1. It is used for filling electric bulbs because of its inert nature

2. It is used in laboratory for handling substances that are air sensitive.

3. Pure argon is used in gas chromatography.

The answer is (c) HF

O₃ is an endothermic compound. On heating it readily decomposes to give dioxygen and nescent oxygen.
O₃ \(\overset{Heat}{\longrightarrow}\) O₂ + [O] (Nascent oxygen)
Since nascent oxygen is very reactive, therefore, O₃ acts as powerful oxidising agent.

• It combines with water vapour present in the atmosphere to form sulphuric acid. This causes acid rain. Acid rain damages soil, plants and buildings, especially those made of marble.
• Even in very low concentrations, SO₂ causes irritation in the respiratory tract. It causes throat and eye irritation and can also affect the larynx to cause breathlessness.
• It is extremely harmful to plants. Plants exposed to sulphur dioxide for a long time lose colour from their leaves. This condition is known as chlorosis. This happens because the formation of chlorophyll is affected by the presence of SO₂.

Fluorine forms only one oxoacid, i.e. HOF because of its high electronegativity and small size.