p Block Elements Class 12

p Block Elements Class 12

p Block Elements

P-block elements are placed in groups 13 to 18 of the right side of the periodic table. The general electronic configuration of p-block elements is ns2np1-6, except helium. They are shiny and are good conductors of heat and electricity. P-block elements include metals, non-metals and metalloids. These are p block elements class 12 notes, published by your chemistry tutor Chemistry Notes Info [www.ChemistryNotesInfo.com].

We learn about s block elements, p block elements and d and f block elements in inorganic chemistry.

p Block Elements Definition

The p-block elements are defined as the elements in the periodic table in which the last electron enters in p-orbital of the atom.

p Block Elements Classification

The p-block elements are classified into six groups as follows-

• Group-13: B, Al, Ga, In, Ti (ns2np1)
• Group-14: C,Si, Ge, Sn, Pb (ns²np²)
• Group-15: N, P, Ar, Sb, Bi (ns²np³)
• Group-16: O, S, Se, Te, Po (ns²np⁴)
• Group-17: F, Cl, Br, I, At (ns²np5)
• Group-18: He, Ne, Ar, Kr, Xe, Rn (ns²np6)

GROUP 15 ELEMENTS OF p BLOCK ELEMENTS

The group 15 elements includes nitrogen (N), phosphorus (P), arsenic (As), antimony (Sb), bismuth (Bi).

As we move down the group in periodic table metallic character increases with increase in atomic number. N and P are non-metal. Ar and Sb are metalloids, while Bi is a metal.

OCCURRENCE

• Nitrogen gas (N2) is occupied by the 78% of total atmosphere. It is main component of proteins, which plays many critical roles in our body. It occurs as sodium nitrate in the earth’s crust.
• Phosphorus occurs as minerals of the apatite family, Ca9[PO4]6.CaX2, (X=F, Cl or OH). It is present in the form of proteins in milk and eggs. It is also present in bones and living cell.
• Arsenic, antimony and bismuth are generally associated with sulphide minerals. The main ores of bismuth are Bi2O3 and sulphide Bi2S3.

ELECTRONIC CONFIGURATION

The general electronic configuration of group 15 elements is ns²np³. The outermost three electrons are unpaired in p-sub shell.

Since d and f sub shell are absent in N, P and present in As, Sb and Bi, that makes N and P behave differently from As, Sb, and Bi.

Elements	Atomic number	Condensed electronic configuration
Nitrogen (N)	7	[He] 2s²2p³
Phosphorus (P)	15	[Ne] 3s²3p³
Arsenic(As)	33	[Ar]3d¹04s²4p³
Antimony(Sb)	51	[Kr]4d¹05s²5p³
Bismuth (Bi)	83	[Xe]4f¹⁴5d¹06s²6p³

PHYSICAL PROPERTIES

• As we move down the group from N to Bi covalent, ionic radii and metallic character increases and value of ionization enthalpy and electronegativity decrease. N is the most electronegative element in the group 15.
• N is a gas and exists as diatomic molecule with a triple bond between the atoms. P, As and Sb probably exist as tetra atomic molecules containing single bonds between each pair of atom. Bi is mono-atomic metal.
• The density, atomic volume and boiling points increase down the group of group 15 elements.

Allotropy of group 15 elements

Allotropy is the existence of two or more different physical forms of a Chemical element.

• Nitrogen in its solid state exists in two form cubic crystal structure and hexagonal crystalline structure.
• Phosphorus exists in three forms namely white, red and black phosphorus. White phosphorus is waxy solid of P4 tetrahedral and it is also available in gaseous state. Red phosphorus has complex chain structure while black phosphorus is thermodynamically stable having layer structure.
• Arsenic and antimony also exists in three allotropic forms. Bismuth does not show allotropy.

Chemical Properties

• Action of air: With oxygen all the elements of group 15 to corresponding oxides on heating.

N2 + O2 → 2NO

• Action of acids: There is no action of hot concentrated nitric acid (HNO3) on nitrogen but with phosphorus and arsenic they forms oxyacids. While Sb and Bi forms oxide and nitrate respectively.

P4 + 20 HNO3 → 4H3PO4 + 20NO2 + 4H2O

• Action of alkalies (NaOH): nitrogen have no action of alkalies, but phosphorus form phosphine and hypophosphite

• Action of metal: nitrogen forms metal nitrides.

          6Li + N2 → 2Li3N

Phosphorus forms metal phosphides.

6Mg + PO4 → 2Mg3P2

Arsenic and antimony forms covalent arsenides and antimonides respectively.

• Reactivity towards hydrogen: in group 15 all elements forms hydrides with formula AH3, where A= N, P, As, Sb, Bi. e.g.NH3, PH3, etc. Basicity and thermal stability these hydrides decreases in the order of NH3>PH3>AsH3>SbH3>BiH3 i.e. down the group.

OXIDATION STATES

• Since the general electronic configuration of group 15 elements is ns²np³ they show common oxidation states of +3, +5 and -3.
• Nitrogen shows wide range of oxidation states from -3 to +3. From N to Bi +3 oxidation state increases and +5 oxidation state decreases.
• Nitrogen in its solid state exist in two form

Nitrogen

Abnormal Behavior of Nitrogen

Nitrogen differs in other elements of the group 15 due to small size, high electronegativity, high ionization enthalpy and absence of d orbital.

1. Nitrogen is gas while all the elements of the group are solids under normal temperature.
2. Nitrogen exists in diatomic molecule (N2) while all the other elements of group exist in tetratomic molecules.(P4, As4, Sb4)
3. Nitrogen can form pπ-pπ multiple bonds while other elements forms dπ-pπ overlapping.
4. Nitrogen does not form penta halides like other elements in group.
5. Nitrogen shows variable range of oxidation states while other elements of group shows limited oxidation states.

Nitrogen is highly electronegative element with absence of d orbital.

Preparation of dinitrogen (N2)

• Commercial method: On commercial scale it is obtained by the fractional distillation of liquid air.
• Laboratory method: It is prepared in the laboratory by reaction of ammonium chloride on sodium nitrite.
• From ammonium dichromate: Dinitrogen is obtained by thermal decomposition of ammonium dichromate.
• From sodium or barrium azide: Nitrogen is obtained in pure form by thermal decomposition of sodium or barrium azide.

Properties of dinitrogen (N2)

• Dinitrogen is present in the atmosphere in gaseous state. It is odourless, colourless, tasteless, chemically inert and non toxic gas.
• It slightly soluble in water and it has low freezing point (195.3K).
• At room temperature it is chemically inert. As temperature increases its reactivity also increases.
• Dinitrogen combines with dioxygen to give nitric oxide at 2000K.
• On reaction with carbide it gives calcium cyanamide.

Compounds of nitrogen

Ammonia (NH3)

Preparation of ammonia

1. Laboratory method: Ammonia is obtained by heating a mixture of NH4Cl and slaked lime Ca(OH)2.
2. Manufacturing method: Ammonia is manufactured by Haber’s process on large scale. In this process N2 and H2 are in proportion 1:3 are allowed to react at high pressure 200×105 Pa and temperature 700K. The catalysts used in this process are Fe2O3, K2O and Al2O3.

Properties of ammonia

• Ammonia is colourless gas having pungent smell and can be toxic.
• It’s freezing point is 198.4K and boiling point is 239.7K.
• It is highly soluble in water to form NH4OH.
• It burns in the excess of air to give dinitrogen and water.
• It reacts with Cl2 to give NCl3.
• It gives amide to react with active metal like Na and K.

Uses of ammonia

It is used to prepare ammonia nitrate, urea, ammonia phosphate, ammonia sulphate, fertilizer, nitric acid and it is also used as refrigerant.

Nitric acid (HNO3)

Laboratory method: By distillation of nitre with concentrated sulphuric acid.

Commercial scale: On large scale nitric acid is prepared by Ostwald’s process. It is prepared by three steps.

1. NH3 is oxidized by atmospheric oxygen in presence of catalyst.
2. Nitric oxide (NO) combines with nitrogen to give NO2.
3. Nitrogen dioxide dissolves in water to gives nitric acid.

Properties of nitric acid

Pure nitric acid is colourless liquid having freezing point 231.4K and boiling point 355.6K. In gaseous state, it is planner molecule. The pure nitric acid is unstable.

Uses of nitric acid

1. Nitric acid is used in the manufacture of organic dyes, varnishes, cellulose.
2. It is used in the preparation of sulphuric acid in lead chambers process.
3. And, it is also used as oxidizer in rocket fuels.

Oxides of Nitrogen

Nitrogen can forms number of oxides in its different oxidation states.

Name of oxide	Oxidation state of Nitrogen	Physical appearance and chemical nature
Dinitrogen oxide (N2O)	+1	Colourless gas, neutral
Nitrogen monoxide (NO)	+2	Colourless gas, neutral, reactive
Dinitrogen trioxide (N2O3)	+3	Brown gas, acidic, reactive
Nitrogen dioxide (NO)	+4	Blue, solid, acidic
Dinitrogen tetraoxide (N2O2)	+4	Colourless solid or liquid, acidic
Dinitrogen pentaoxide (N2O5)	+5	Colourless ionic solid, unstable acidic

PHOSPHORUS

Allotropic forms of phosphorus

Phosphorus is present in three allotropic forms. Viz. White, red and black phosphorus.

1. White phosphorus: It is translucent, white waxy solid insoluble in water. It is stored in water to protect from air. It has tetrahedral structure (P4).
2. Red phosphorus: It is tasteless, odourless, non-poisonous reddish violet solid in powder form. It is less reactive than white phosphorus. In red phosphorus P4 tetrahedral units are linked to each other to form chain.
3. Black phosphorus: It is thermodynamically most stable allotrope. It does not react with water. It has two different forms α-black phosphorus and β-black phosphorus.

Compounds of phosphorus

Phosphine (PH3)

Preparation: phosphine is prepared by action of water on calcium or aluminium phosphide.

Properties of phosphine: It is colourless gas having odour of rotten fish. It is highly poisonous and soluble in water. It does not react with acid and alkalies but reacts with oxygen to form explosive.

Uses of phosphine: It is used in preparation of smoke screens, organo phosphorus compound. It is used as powerful reducing agent.

Phosphorus halides

Phosphourus can form two types of halides namely phosphorus tricloride with general formula PX3 and phosphorus pentacloride with formula PX3 (X=F, Cl, Br, I)

GROUP 16 ELEMENTS OF p BLOCK ELEMENTS

Group 16 elements include oxygen (O), sulphur (S), selenium (Se), tellurium (Te) and polonium. Since first four elements of group forms ore i.e. oxides, sulphides etc. with number of metals they are called as chalcogens.

OCCURRENCE

Oxygen is present by mass 46.6% and in atmosphere 21% by volume. Oxygen is most abundant element. Sulphur is less abundant. Selenium and tellurium occurs as sulphide while radioactive pollonium occurs by decay of thorium and uranium.

ELECTRONIC CONFIGURATION

The valence shell electronic configuration of group 16 is ns²np⁴.

Elements	Atomic number	Condensed electronic configuration
Oxygen	8	[He]2s²2p⁴
Sulphur	16	[Ne]3s²3p⁴
Selenium	34	[Ar]3d¹
Tellurium	52	[Kr]4d¹05s²5p⁴
Polonium	84	[Xe]5d¹06s²6p⁴

Trends in physical properties

• Except oxygen (O2) all the other elements of group are solid at common temperature.
• Sulphur and Selenium is exist in crown puckered ring structure of eight atoms.
• Due to addition of new shell the atomic as well as ionic radii increases down the group.
• Metallic character increases down the group. Sulphur is non-metal, selenium and tellurium are semi – metals while polonium is metal.
• Oxygen shows less possibility towards catenation. The tendency of catenation decreases down the group.
• The density of group increases down the group due to increase in atomic mass
• Melting and boiling point increases down the group (except Po).
• Oxygen is second most electronegative after fluorine. The value of electronegativity decreases down the group.

Chemical properties

• The reactivity of elements decreases down the group. The group 16 elements react with oxygen to form dioxides.

S + O2 → SO2

• Sulphur reacts with alkalies to form sulphides and sulphites with non metal group 16 elements combine directly.
• All the group 16 elements are weakly acidic and acts as weak diprotic acids.
• All the hydrides of these groups are reducing agent (except H2O).
• These elements of group can form large number of halides with formula AX6, AX4 and AX2 where A is elements of group 16.

Abnormal behavior of oxygen

• oxygen differs from all the elements in the group ion several properties due to its
  • Small size
  • Absence of d orbital
  • High electromagnetivity
• Oxygen is a gas while other elements are solid.
• Hydride of oxygen is in liquid state i.e. H2O while others are in gaseous state.
• Molecular oxygen is paramagnetic while others elements are diamagnetic.
• Oxygen exist in diatomic molecule O2 while other elements are in polyatomic.

Dioxygen (O2)

Preparation

1. Naturally by photosynthesis

Dioxygen is produced in atmosphere in large quantity by photosynthesis of green plants.

xH2O + xCO2 sunlight→ (CH2O)X + xO2 (g)

2. Laboratory method

In this method dioxygen is prepared by heating KClO3 using catalyst MnO3.

2KClO3 → 2KCl + 3O2(g).

3. Commercial method

On large scale O2 is prepared by two methods.

1. From water: By electrolysis of acidified water, O2  gas is obtained at canoed.
2. From air: O2 is obtained by fractional distillation of liquid air.

4. By thermal decomposition

1. Dioxygen can obtained by thermal decomposition of oxygen rich salts and metallic oxides.

2KNO3 → 2KNO2 + O2

2H2O2 → 2H2O + O2

Properties of Dioxygen (O2)

1. Dioxygen is odourless, colourless and tasteless gas which is heavier than air.
2. It is paramagnetic, it is also present in water in dissolve form which help to sustaining life of plants and animals in water.
3. It has three stable isotopes i.e. 16O, 17O, 18O.
4. It does not show much chemical reactivity, it is quite stable at normal temperature.
5. Dioxygen is not combustible but supports combustion. It forms oxides with different forms of metal.

Oxides are classified into three types:

1. Acidic oxides: The oxide which combines with water to give an acid is called as acidic oxides.
2. Basic oxides: The oxides which combines with water to give an base is called as basic oxides.
3. Amphoteric oxides: The oxides which show acidic and basic characteristics are called as amphoteric oxides.

Uses of dioxygen (O2)

1. It is most important gas for all living organism in respiration.
2. Dioxygen is used firemen, sea divers, miners, aviators and also useful for artificial respiration in hospitals.
3. It is used in rocket fuel, metallurgical processes and in preparation of large number of compounds.

Ozone (O3)

By the action of electrical discharges or ultraviolet radiation on dioxide (O2) ozone can be obtained.

It is present at the height of 20km from earth surface. This layer is called ozonosphere. Ozone (O3) prevents entry of harmful high energetic ultraviolet (UV) rays. It is formed in atmosphere naturally through photochemical reaction.

Preparation of ozone (O3)

By laboratory method slow dry stream of dioxide (O2) is passed through a silent electric discharge dioxide (O2) gets converted into ozone (O3).

    3O2 → 2O3            ΔH=+284KJ

Properties of ozone (O3)

1. Ozone is thermodynamically unstable having pungent odour.
2. Solid ozone is violet black, liquid ozone is blue black and gaseous ozone is blue.
3. In higher concentration it is very dangerous explosive.

Uses of ozone (O3)

1. It is used as disinfectant and germicide sterilize air and water bleaching agent for starch, oils, waxes, flour etc.
2. In industry it is used in the manufacture of silk and camphor.
3. It prevents the harmful ultraviolet (UV) rays of sun from reaching the earth surface.

Sulphur (S)

In free states sulphur occurs in the volcanic regions. It is also occurs in combined state as sulphides (feS2, ZnS, HgS, Cu2S) and sulphates (MgSO4.7H2O, CaSO4.2H2O). Sulphur exists in different allotropic forms as follows

1. Rhombic sulphur
2. Monoclinic sulphur
3. Cyclo – S6
4. Milk of sulphur
5. Plastic sulphur
6. Sn molecular sulphur
7. Colloidal sulphur

Compounds of sulphur (S)

Below are compounds of sulphur.

Sulphur dioxide (SO2)

Preparation

• Sulphur dioxide (SO2) is obtained when sulphur burnt in air.

              S(s) + O2(g) → SO2(g)

• In laboratory method Sulphur dioxide (SO2) is obtained by the action of sulphuric acid on copper turnings.

     Cu + 2H2SO4 → CuSO4 + SO2+ 2H2O

• On commercial method it is on large scale as a by product of the roasting of pyrites.

     4FeS2 + 11O → 2Fe2O3 + 8SO2

Properties of sulphur dioxide (SO2)

• Sulphur dioxide (SO2) is colourless with pungent and suffocating smell.
• It is highly soluble in water to forms sulphurous acid, H2SO3.

SO2 + H2O → H2SO3

• Its boiling point is 263K. In solid state it forms discrete molecules.
• It is reducing agent.

Uses of sulphur dioxide (SO2)

1. It is used in the manufacture of H2SO4 and refining of petroleum and sugar industry.
2. It is used as disinfectant, preservative germicide, bleaching agent and solvent

Sulphuric acid (H2SO4)

Manufacturing process

• Contact process: This process involves four basic steps.
• Preparation of sulphur dioxide (SO2) from sulphur

S(g) + O2(s) → SO2

• Oxidation of sulphur dioxide (SO2) and sulphur trioxide (SO3) by using catalyst vanadium pentaoxide (V2­O5).

2SO2 + O2 ↔ 2SO2

• By dissolution of sulphur trioxide (SO3) in sulphuric acid (H2SO4), oleum(H2S2O7) is obtained

SO3  +  H2SO4  → H2S2O7

• Dilution of oleum (H2S2O7) to give sulphuric acid  (H2SO4).

H2S2O7 + H2O → 2 H2SO4

• Lead chamber process: in this process a mixture of SO2, NO and airis treated with steam to obtain H2SO4.

2SO2 + O2 + 2H2O → 2 H2SO4

Properties of sulphuric acid (H2SO4)

• Sulphuric acid (H2SO4) is colourless, dense, oily liquid with boiling point 611K and freezing point 283K.
• It is strong acid, less volatile and highly viscous due hydrogen bonding. It is known as king of chemicals.
• It acts as dehydrating agent with many organic compounds.

HCOOH( Formic acid ) H2SO4→ CO + H2O

C6H12O6 (Glucose) H2SO4→ 6C + 6H2O

• It also acts as a oxidizing agent.

S + H2SO4 → 3SO2 + H2O

P4O10 + 6H2O → 4H3PO4

• When metals are treated with sulphuric acid (H2SO4) gives out hydrogen.

Fe + H2SO4 → FeSO4 + H2

Uses of sulphuric acid H2SO4

1. It is used in preparation of HNO3, HCL, H3PO4, Na2CO3, sulphade, oleums, ether.
2. It is most important chemical in many industries for manufacturing of dyes, fertilizers, detergents, explosives etc.
3. It is in used lead storage batteries. It is also used as laboratory reagent dehydrating agent and oxidizing agent.

GROUP 17 ELEMENTS (HALOGENS) OF p BLOCK ELEMENTS

The group 17 elements include elements fluorine (F), chlorine (Cl), bromine (Br), iodine (I) and astatine (At). These elements are highly electronegative which are found in sea water as salts. Astatine is radioactive element.

Electronic configuration

The outermost shell electronic configuration is ns2np5. Each of them is only short of one electron to get stable noble gas electronic configuration.

Elements	Atomic number	Condensed electronic configuration
Fluorine (F)	9	[He] 2s22p5
Chlorine (Cl)	17	[Ne] 2s22p5
Bromine (Br)	35	[Ar] 3d104s24p5
Iodine (I)	53	[Kr] 4 d105s25p5
Astatine (At)	85	[Xe] 4f145d106s26p5

Physical properties

1. All these elements of group 17 are exist in diatomic form F2, Cl2, Br2 etc. F and Cl are in gaseous state while Br is liquid and I is in solid state at normal temperature.
2. On moving the down the group 17 atomic and ionic radii increases while ionization enthalpy decreases.
3. All the element of group possess very high value of electronegativity, fluorine is the most one. These values decrease down the group to iodine.
4. All halogens are typical non metals having low melting and boiling points.
5. To attain stable noble gas configuration halogen shows common oxidation state – 1. They also show positive oxidation state +1, +3, +5 and +7.

Chemical properties

1. Halogens are highly reactive elements. The reactivity decreases down the group.
2. Halogen has a strong tendency to accept an electron to form anions.

1/2X2 + e– → X–    (X = F, Cl, Br, I)

They act as a strong oxidizing agent.

• On reaction with metals and non metals halogen forms halides

Cu + F2 → CuF2

2AI + 3Br2 → AI2Br6

• Halogen reacts with hydrogen to give hydrogen halides.

H2 + F2 → 2HF

H2 + Cl2 → 2HCl

• All the halogen reacts with NaOH to form halides and hypohalides.

2NaOH + 2Cl2 → NaCl + NaOCl + H2O

• Halogen combines amongst themselves from many compounds known as inter halogen compounds.

Abnormal behavior of Fluorine (F)

Fluorine’s abnormal behavior due to

1. High electronegativity.
2. Small size.
3. Low F-F band dissociation energy.
4. Non availability of d – orbital in its valance shell.
5. It is highly reactive element which forms hydrogen bondings in its hydrides. It exhibits only in -1 oxidation state.

Chlorine (Cl)

The Chlorine is greenish yellow poisonous gas, occurs in extents of 0.14%in the earth crust. And, Chlorine is also presents in sea water as KCl, MgCl and CaCl2.

Preparation of Cl2

• 1. By the oxidation of HCl on manganese dioxide (MnO2).

MnO2 + 4HCl → MnCl2 + Cl2 + H2O

• 2. On commercial scale it is obtained by
• 2.1 Deacon process: HCI is oxidized by Atmospheric oxygen.

4HCl + O2 → 2Cl2 + H2O

• 2.2 Electrolytic process: This process involves the electrolysis of an aqueous solution of brine (NaCl).

Properties of chlorine

1. It is poisonous, greenish yellow gas with suffocating, pungent smell and heavier than air.
2. It is soluble in water and the solution is called chlorine water.
3. Chlorine is neither combustible nor supports combustion. It reacts with number of metals to form their chlorides.

2Na + Cl2 → 2NaCl

2K + Cl2 →2KCl

• It dissolves in water to form mixture of HCl and HOCl (hypochloric acid).

Cl2 + H2O ↔ HCl + HOCl

• Chlorine reacts with hydrogen with very high affinity to form HCl.

H2 + Cl2 → 2HCl

Uses of chlorine

1. It is use as bleaching agent, for sterilization, extraction of metals like gold and platinum.
2. It is use in manufacture in bleaching powder, dyestuff, explosives, refrigerant, several poisonous gases, hydrochloric acid, plastics, insecticides and several industry solvents.

Hydrochloric Acid (HCl)

It is colourless gas with pungent odour. In liquid its boiling point is 189K and melting point is 159K. It is highly soluble in water. Hydrogen chloride (HCl) is prepared laboratory by heating a mixture of sodium chloride and concentrated sulphuric acid.

NaCl + H2SO4 → NaHSO4 + HCl

Uses of Hydrochloric Acid HCl

It is used in manufacture of chlorine, ammonium chloride, and glucose. It is also used in medicine, galvanizing, preparation of H2 and as a laboratory reagent.

Inter halogen compound

The compound obtained from different halogen are called inter halogen compound. The general composition of inter halogen compounds are XX’, XX’3, XX’5 and XX’7 where X is electropositive group halogen elements.

XX’	XX3’	XX5’	XX7’
ClF	ClF3	ClF5	IF7
BrF	BrF3	BrF5
BrCl	IF3	IF5
ICl	ICl3 (unstable)

These compounds can be prepared by the direct combination or by action of halogen on lower interhalogen compounds. Inter-halogen compounds are covalent, volatile, unstable and diamagnetic in nature.

GROUP 18 ELEMENTS (NOBLE GASES) OF p BLOCK ELEMENTS

Group 18 elements include helium, neon, argon, krypton, xenon and radon. These elements are also called as noble or inert gases.

All the elements of group 18 exist in the form of gases in atmosphere. About 1% by volume of air is occupied by noble gases. They are chemically unreactive.

Noble gas have very stable electronic configuration. The valence shell electronic configuration of these elements is ns2np6.

Elements	Atomic number	Condensed electronic configuration
Helium (He)	2	1s2
Neon (Ne)	10	[He]2s22p6
Argon (Ar)	18	[Ne]3s23p6
Krypton (Kr)	36	[Ar]3d104s24p6
Xenon (Xe)	54	[Kr]4d105s25p6
Radon (Rn)	86	[Xe]4f145d106s26p6

Physical properties

1. All the elements are colorless, odorless, and tasteless.
2. All the elements are always occurs in free the state in nature in monoatomic.
3. Atomic radii and tendency to liquify increases on moving down the group.
4. They require a very large amount of energy to remove an electron because of their stable electronic configuration hence value of ionization enthalpy is very high.
5. Noble gases have low melting and boiling point. They are slightly soluble in water.

Chemical unreactivity

Due to –

• 1) completely filled valence shells
• 2) High and positive value of electron gain enthalpy and
• 3) High ionization enthalpy

noble gases do not take part in chemical reactions i.e. they are chemically unreactive elements. 

There are so many uses of noble gases in our daily life.

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पानी के तीन रूप : जल की तीन अवस्थायें: ठोस, द्रव, और हवा

जून 7, 2019अभिनव शिक्षा, रसायन विज्ञान शब्दावली, विज्ञान की बातJitendra Singh Sandhu

जल की तीन अवस्थायें: द्रव, ठोस (बर्फ), और हवा – 3 States of Water: Solid, Liquid and Water

• पानी तीन अवस्थाओं में मौजूद है यानी सॉलिड (आइस), लिक्विड (पोर्टेबल वॉटर, सी वॉटर, ड्रिंकिंग वाटर आदि), गैस (स्टीम, वैपर्स)।
• इन तीनों अवस्थाओं में पानी के अलग-अलग भौतिक गुण हैं लेकिन एक ही रासायनिक संरचना यानी H2O है
• पानी की इन अवस्थाओं की विशेषताएं, ‘आणविक ऊर्जा और उनके अणु कैसे एकत्रित होते हैं, इस पर निर्भर करते हैं।
• जैसे अणु अपनी भौतिक स्थिति (तरल से गैस, गैस से तरल, गैस से ठोस आदि) में परिवर्तन करते हैं, पदार्थ के रासायनिक गुणों में कोई परिवर्तन नहीं होता है, लेकिन रासायनिक प्रतिक्रिया की दर में कुछ परिवर्तन हो सकते हैं।

जल की तीन अवस्थायें – पानी के विभिन्न रूपों की तस्वीरें

ठोस => बर्फ

तरल => पीने का पानी

गैस => भाप

श्यानता (Viscosity) क्या है What is Viscosity

श्यानता (Viscosity) क्या है What is Viscosity

श्यानता (Viscosity) क्या है

पता है! “श्यानता (Viscosity या Shyanta या चिपचिपाहट) क्या है”। चिपचिपाहट के बारे में समझने के लिए, हम हनी और वाटर जैसे कुछ तरल पदार्थों का उदाहरण लेते हैं। जैसा कि हम जानते हैं कि शहद पानी से अधिक गाढ़ा होता है। इसलिए शहद पानी की तुलना में फर्श पर बहुत धीमी गति से बहता है, क्योंकि पानी बहुत कम गाढ़ा होता है इसलिए यह जल्दी बह जाता है। इसलिए हम कह सकते हैं कि अधिक चिपचिपे (जैसे शहद) तरल पदार्थ धीरे-धीरे बहते हैं और इनमें बहुत अधिक चिपचिपाहट होती है। लेकिन बहुत कम चिपचिपा होने वाला तरल जल्दी से बह जाता है। और उस तरल (जैसे पानी) में बहुत कम चिपचिपापन होता है।

श्यानता या चिपचिपापन की परिभाषा

चिपचिपाहट को प्रवाह के प्रतिरोध के रूप में परिभाषित किया जा सकता है।

चिपचिपापन या विस्कोसिटी क्या है

हम कह सकते हैं कि चिपचिपाहट द्रव का आंतरिक प्रतिरोध है। जिन तरल पदार्थों में चिपचिपाहट अधिक होती है, वे स्थानांतरित होने का विरोध करते हैं, क्योंकि इसका आणविक श्रृंगार इस द्रव को गति के लिए बहुत अधिक आंतरिक घर्षण देता है। जबकि तरल पदार्थ जिनकी चिपचिपाहट कम होती है, वे स्थानांतरित होने के लिए कम प्रतिरोध करते हैं, क्योंकि इसका आणविक श्रृंगार इस द्रव को गति के लिए कम आंतरिक घर्षण देता है। इसलिए हम कह सकते हैं कि आणविक श्रृंगार उनके बीच आंतरिक घर्षण का फैसला करता है और जो अंत में द्रव की चिपचिपाहट प्रदान करता है। शहद में पानी की तुलना में अधिक आंतरिक घर्षण होता है इसलिए शहद में पानी की तुलना में अधिक चिपचिपाहट होती है।

तरल या तरल पदार्थों के साथ, गैसों में भी चिपचिपापन होता है लेकिन साधारण परिस्थितियों में गैसों की चिपचिपाहट को नोटिस करना बहुत मुश्किल होता है।

केमिस्ट्रीनोटइन्फोडॉटकॉम द्वारा चिपचिपाहट रसायन विज्ञान के नोट्स को सरल तरीके से समझने के लिए, हम कह सकते हैं कि, “चिपचिपापन एक तरल पदार्थ का अपने आकार में परिवर्तन का प्रतिरोध है”, चिपचिपाहट प्रवाह के लिए प्रतिरोध है। तरलता चिपचिपाहट का पारस्परिक कारण है, इसलिए अब हम कह सकते हैं कि शहद में बहुत अधिक चिपचिपाहट और कम तरलता है। जबकि पानी में चिपचिपाहट कम और तरलता अधिक होती है।

स्नेहन और परिवहन, छिड़काव, सतह कोटिंग, इंजेक्शन मोल्डिंग आदि में प्रयुक्त तरल पदार्थों की विशेषताओं को निर्धारित करने में चिपचिपाहट बहुत महत्वपूर्ण भूमिका निभाती है।

चिपचिपापन का सूत्र

चिपचिपापन = बल × समय / क्षेत्र

चिपचिपापन की इकाई

चिपचिपाहट की इकाई न्यूटन सेकंड / वर्ग मीटर (Ns/m2) है

चिपचिपाहट की SI इकाई पास्कल सेकंड (पास) है

तापमान के साथ चिपचिपाहट का संबंध

तापमान में वृद्धि के साथ तरल पदार्थों की चिपचिपाहट कम हो जाती है, जबकि तापमान में वृद्धि के साथ गैसों की चिपचिपाहट बढ़ जाती है।

तापमान ->	27 °C	77 °C
पानी की चिपचिपाहट	0.85×10-3 pascal second	0.36×10-3 pascal second
वायु की चिपचिपाहट	1.85×10-5 pascal second	2.08×10-5 pascal second

श्यानता (Viscosity या Syanta या चिपचिपाहट) का मापन

Viscosity को विभिन्न प्रकार के Rheometers या Viscometers द्वारा मापा जाता है।

Biomolecules Class 12

Biomolecules Class 12

Biomolecules

In these chemistry notes, we learn about biomolecules class 12 chemistry. Some state boards books also contain these notes in 11th class chemistry book i.e. Biomolecules class 11. We prepare chemistry notes as per biomolecules class 12 ncert book, that is good for both classes of students.

Cell is the basic unit in all living organisms. Cell has very complicated structure and contains a large number of lifeless molecules.

Biomolecules Definition

The Biomolecules are lifeless molecules which combine in specific manner to produce life or control biological reactions. We can also say that, Bio-molecule is a molecule that is produced by a living organism.

Biomolecules Chemistry

Biomolecules in chemistry may be simple molecule like water, minerals, salts, vitamins, hormones etc. or macro-molecules like carbohydrates, proteins lipids (fats and oils) etc. They play an important role in function of organisms. The chief constituents of our diet are carbohydrates and proteins.

Biomolecules Notes

Carbohydrates are major source of energy. Proteins are nitrogenous substances present in hair, skin, muscle, nails etc. which plays variety of role in proper functioning of the living organisms. Enzymes which catalyze chemical reaction that take place in cell are proteins. Lipids are a source of stored energy. RNA (Ribonucleic Acid) and DNA (Deoxyribonucleic Acid) present in the nucleus of the cell are responsible for the storing genetic characteristics and synthesis of proteins.

Biomolecules Class 12th

Biomolecules are optically active polyhydroxy aldehydes or polyhydroxy ketones or the compounds that can be hydrolysed to polyhydroxy aldehydes or polyhydroxy ketones.

CARBOHYDRATES

• Early chemist noticed that carbohydrates had molecular formula      which could be represented as Cx(H2O). They were considered to be hydrates of carbon hence the name was given as carbohydrates.
• Later studies revealed that these compounds were not hydrates of carbon because they did not contain free water molecules.
• Similarly the compounds which fit into this formula are not classified as carbohydrates. e.g. formaldehyde HCHO, acetic acid CH3COOH, fit into this formula but are not carbohydrates.
• Rhamnose C6H12O5 does not fit into this formula but are carbohydrate. You read these Biomolecules class 12 notes of NCERT chemistry on ChemistryNotesInfo.com

Classification of carbohydrates

On the basis of their hydrolysis products, carbohydrates are classified as:

Simple carbohydrates

• Simple carbohydrates are also known as monosaccharides cannot be hydrolyzed further to any simpler compound. They are basic unit of all carbohydrates.
• Monosaccharides are further classified as (1) aldoses, containing aldehyde (CHO) group (2) ketoses, containing keto group.
• Depending upon number of carbon atoms and functional group, monosaccharides are further classified as triose having three carbon atoms, tetrose having four carbon atoms, pentose having five carbon atoms etc.

Complex carbohydrates

It is further classified as oligosaccharides and polysachharides

Oligosaccharides

An oligosachharide is carbohydrate (sugar) which on hydrolysis gives two to ten monosachharides units.

Depending upon number of monosachharides units produced on hydrolysis oligosaccharides are further classified as:(On hydrolysis)

• Disaccharides (C12H22O11) :

Sucrose        ——>           Glucose + Fructose

Maltose  ——>  Glucose + Glucose

Lactose   ——>  Glucose + Galactose

• Trisaccharides (C12H32O6) :

Raffinose   ——>  Glucose + Fructose + Galactose

• Tetrasaccharides (C24H42O21) :

Stachyose   ——>  Glucose + Fructose + Galactose + Galactose

Polysaccharides

A carbohydrate that on hydrolysis yields large number of monosaccharide units is called polysaccharide. It is non-sugar. Polysaccharides are tasteless, amorphous, insoluble in water and natural biopolymers of monosaccharides e.g. starch, cellulose, glycogen, gums etc.

Fischer Projection Formula

A tetrahedral carbon atom is represented in a fischer projection by two crossed lines. The horizontal line represents bonds coming out of the page and vertical lines represent bonds going into the page.

D- and L- Sugars

• The dextorotatory enantiomer of glyceraldehyde occurs naturally and represented as (+) – glyceraldehyde. It is referred as D – glyceraldehyde.
• The leavorotatory enantiomer of glyceraldehyde is represented as (-) – glyceraldehyde and referred as L – glyceraldehyde.
• In fischer projection, if the hydroxyl group at lowest chirality center points to the right, the monosaccharide is referred to be D – sugar.
• Whereas monosaccharide having the hydroxyl group at lowest chirality center pointing to the left is referred to be L – sugar. 
  

GLUCOSE

Glucose is present in most of the sweet fruits, grapes, cane sugar, honey and in polysaccharides like starch and cellulose. It is also an essential component of human blood. Naturally occurring glucose is dextrorotatory and known as dextrose.

Preparation of glucose

• From sucrose (laboratory method)

Glucose is prepared in the laboratory by hydrolysis of sucrose by boiling it with dilute hydrochloric acid or dilute sulphuric acid for about two hours.

C12H22O11 + H2O —–> C6H12O6 +C12H12O6

                                            Glucose    Fructose

• From starch (commercial method)

When starch is boiled with dilute sulphuric acid at 393K under pressure it undergoes hydrolysis to give glucose. Excess of sulphuric acid is neutralized by adding chalk powder.

(C6H10O5)­n + nH2O —–> nC6H12O6

Open chain structure of glucose

Glucose was assigned the open chain structure given below, on the basis of following evidences. 

1. The molecular formula of glucose was found to be C6H12O6 from the elemental analysis and molecular weight determination experiments.
2. Action of HI: glucose prolonged heating with HI gives n-hexane, indicates that all the six carbon atoms are linked in straight carbon chain.
3. Action of hydroxyl amine: Glucose reacts with hydroxyl amine in an aqueous solution to form glucose oxime. This indicates the presence of CHO group in glucose.
4. Action of hydrogen cyanide: Glucose reacts with hydrogen cyanide to form glucose cynohydrin.
5. Action of bromine water: Glucose on oxidation with bromine water gives gluconic acid, which shows that the carbonyl group in glucose is aldehyde group.
6. Action of acetic anhydride: When glucose is heated with acetic anhydride in the presence of catalyst pyridine, glucose penta acetate is formed. It indicates that glucose is stable compound Action of dilute nitric acid: glucose as well as gluconic acid on oxidation with dilute nitric acid forms saccharic acid. This indicates the presence of a primary alcoholic group (-CH2OH) in glucose.

Spatial arrangement of different -OH groups in glucose as follows-

Cyclic structure of glucose

Open chain structure does not explain following reaction and facts.

1. Glucose in spite having aldehyde group does not give condensation reaction with 2,4 dinitro- phenyl hydrazine, addition reaction with sodium bisulphite and gives negative test with schiff base.
2. Glucose penta- acetatedoes not condense with hydroxyl amine indicating the absence of aldehyde group.
3. Glucose is found to exist in two different crystalline form α and β, called anomers. On crystallization from hot and aqueous solution, α- glucose is obtained at 303K while β-glucose is obtained at 371K.

Cyclic six-membered structure of glucose are called pyranose structures, in analogy  with pyran. Pyran is a heterocyclic compound with one oxygen atom and five carbon atoms in the ring.

Haworth Projection Formula of Glucose Biomolecules

The substituents that are to right in a fischer projection formula. Orient the haworth projection formula with the ring oxygen at the back and the anomeric carbon at the right.

Haworth projection formula of glucose

FRUCTOSE

Fructose is made by isomerization of glucose. Fructose is the sweetest. On the basis of different reaction it is shown that, fructose is penta-hydroxyl ketone. The open structure of fructose is as follows.

The cyclic five-membered structures of fructose are called furanose structures in analogy with furan in a heterocyclic compound with one oxygen atom and four carbon atoms in the ring.

Haworth Projection Formula of Fructose Biomolecules

Disaccharides

A carbohydrate that on hydrolysis gives two same or different monosaccharide units is called disaccharide. In disaccharides, anomeric carbon of one monosaccharide molecule is bounded to a carbon of another monosaccharide molecule through an oxygen atom. Such a linkage between two monosaccharide molecules through oxygen is called glycosidic linkage. e.g. – sucrose, maltose, cellobiose, lactose.

Sucrose

Sucrose is known as cane sugar or common table sugar. In sucrose, C-1 of α-D-glucopyranose is linked to C-2 of β-D-fructofuranose by glycosidic linkage. On hydrolysis sucrose give equimolar mixture of dextrorotatory glucose and laevorotatory fructose. It is invert sugar.

Maltose

Maltose is obtained by partial hydrolysis of starch. In maltose C-1 of one α-D-glucopyranose is linked to C-4 of another α-D-glucopyranose molecule by glycosidic linkage. Thus maltose contains 1—>4α glycoside bond. Maltose is a reducing sugar.

Cellobiose

Cellobiose is obtained by partial hydrolysis of cellulose. In cellobiose, C-1 of one β-D-glucopyranose is linked to C-4 of another β-D-glucopyranose molecule by glycosidic linkage. Thus cellobiose contains 1—>4β glycoside bond. Cellobiose is also reducing sugar.

Lactose

Lactose is known as milk sugar. In lactose, C-1 of β-D-glycopyranose is linked to C-4 of β-D-glucopyranose by glycoside linkage. Thus lactose also contains 1—->4β glycoside bond. Lactose is also reducing sugar.

Polysaccharides (C6H10O5)n

A carbohydrate that on hydrolysis yields large number of monosaccharide unit is called polysaccharides. In polysaccharides, a large number of same or different monosaccharaides are linked together by glycosidic linkages.

Starch

The Starch is mainly found in cereal grains, roots, tubers, potatoes etc. it is an important part of our diet. Starch is polymer of α-D-glucopyranose and consists of two fractions, amylose and amylopectin.

Amylose is water soluble component and constitutes about 20% of starch. It is long chain unbranched polymer Amylopectin is insoluble in water and constitutes about 80% of starch. It is a branched chain polymer.

Cellulose

Cellulose is the principal component of plant structure viz. wood, cotton to support the weight of the plant. Cell wall of the plant is made up of cellulose. It is long chain unbranched polymer.

Cellulose contains 1—>4β glycosidic linkages like cellobiose. Humans cannot hydrolyze cellulose due to lack of enzyme required for hydrolysis, hence they cannot use it directly as a food.

Glycogen

The glycogen is stored in animal body in the form of glycogen. It also known as animal starch, because its structure is similar to amylopectin Which is fraction of starch. Glycogen is highly branched.

Importance of carbohydrates bio molecules

1. Carbohydrates are essential for life in both plants and animals.
2. They form major part of our food and store chemical energy in plants.
3. They act as the major source of energy for all the animals.
4. In the plants they are important constituent of supporting tissues e.g. cellulose in wood, cotton in clothes.
5. The main source of energy of animals is glucose which is in the form of glycogen.

PROTIENS

1. Proteins are the biopolymers of a large number of α-amino acid and they are naturally occurring polymeric nitrogenous organic compound containing 16% nitrogen and peptide linkages (-Co-NH-)
2. Successive amino acids are joined together to form protein.
3. It is present in hair, skin, muscle.
4. Common source of proteins is egg, fish, cereals, milk etc.
5. Proteins on hydrolysis give α amino acid.

Peptide bond and polypeptide

• The amide linkage (-Co-NH-) by which α-amino acids are joined in linear fashion in proteins is called peptide linkage.
• Peptide linkage is an amide formed between –COOH and NH3 group by elimination of water.
• When many molecules of amino acid joined together by peptide linkages they form polypeptide which is proteins.

Classification (on the basis of molecular shape)

• Fibrous proteins: The proteins in which the polypeptide chains lie side by side to form fiber like structure. The polypeptide chain held together by hydrogen bond. Example: keratin ( in hair, skin, nails)

• Globular proteins: The proteins have intramolecular hydrogen bonding and are folded to form spherical structures are called globular proteins. Example: haemoglobin (in blood)

Structure of proteins

Each structure of protein is more complex than previous one.

Primary structure

In primary structure, proteins contain polypeptide chain. Amino acids linked with each other in specific sequence in protein this sequence is known as primary structure.

Secondary structure

In a protein, long amino acid chain is coiled, looped, or folded then this Structure of protein is known as secondary structure. It has two different types 

• A polypeptide chain gets coiled by twisting into right handed spiral is known as α-helix.
• The polypeptide chains are converted into flat sheet by stretched out. The contraction results in a pleated called β-pleated sheet.

Tertiary structure

α-helix bend on twist and folding gives three dimensional structure is known as tertiary structure.

Quaternary structure

The spatial arrangement of polypeptide chain with respect to each other is known as quaternary structure.

Amino acids

• Α-amino acids are derivatives of carboxylic acids obtained by replacing α-H by amino group.
• Amino acids contain two functional groups –COOH and -NH2. On hydrolysis protein gives about 30 amino acids. All amino acids have trivial names. E.g. Gly, Val, Glu, Met etc.
• Amino acids are crystalline, colourless, non volatile, high melting solid. In aqueous solutions it behaves like salts.

Amino Acids Classification

Amino acids are classified into –

Acidic amino acid

If numbers of carboxyl groups are more than amino groups the amino acids are acidic. Example-glutamic acid.

Basic amino acid

If numbers of amino groups are more than carboxyl groups, then amino acids are basic in nature. Example-lysine.

Neutral amino acids

The amino acid having equal number of carboxyl and amino groups are called neutral amino acids. Example-valine

ENZYMES

All biological or bio-catalysts which catalyze the reaction in living organisms is called enzymes. All enzymes are protein. Enzymes help in the digestion of food and absorption of certain molecule producing energy. Enzyme maltase converts maltose to glucose.

    C12H22O11 ( Maltose ) —–> C6H12O6 ( Glucose )

LIPIDS

Now we learn about lipids. Lipids form naturally occurring biomolecules of a diverse group having limited solubility in water and can be isolated from organism by extraction with non polar solvents. Also, Lipids have variety of function in living organisms.

Lipids Classification for Biomolecules chapter class 12

The Lipids are classified as

Complex lipids

Complex lipids are esters of long chain fatty acid and can be hydrolyzed. They include triglycerides (animal fats and vegetable oils), glycolipids, phospholipids and waxes. 

Simple lipids

Simple lipids do not have ester linkages and they cannot be hydrolyzed. They include steroids, tarpenes and prostaglandins.

HORMONES

Hormones are the secretion of endocrine glands (ductless glands). They regulate vital functions of body and produced in very small quantity like enzymes. They have low molecular weight and are easily diffusible.

Functions of hormones

1. The hormone thyroxine is secreted by thyroid gland in the neck to increase the rate of energy exchange and consumption of oxygen.
2. Insulin is peptide hormone, secretes in pancreas and controls carbohydrate metabolism by increasing glycogen in muscles and oxidation of glucose in tissue and also lowers the blood sugar.

VITAMINS

Vitamins are organic compounds which are required in the diet in small quantity to perform biological function and proportionate growth in living beings. Enough supply of vitamins is obtained from a well balanced diet.

Vitamins Classification

Depending upon the solubility

Water soluble vitamins (B and C)

Vitamins B and C are soluble in water. They are readily excreted in urine, have low toxicity and cannot be stored in body.

Fat soluble vitamins (A, D, E, K and P)

Vitamins A, D, E, K and P are soluble in oils and fats and are stored in the body in liver and in tissue.

Depending upon chemical structure

• First, Vitamins of aliphatic series e.g. vitamin C
• Second, Vitamins of aromatic series e.g. vitamin K
• Third, Vitamins of alicyclic series e.g. Vitamin A
• Fourth, Vitamins of heterocyclic series e.g. vitamin B

NUCLIEC ACID

Nucleus is present in every cell of living organisms. Nucleus has acidic properties and hence it was named as nucleic acid. It is the substance of heredity. Nucleotide is the structural unit of nucleic acid. It has three components they are as follows.

1. Sugar: It has deoxyribose sugar in DNA and ribose sugar in RNA. It is pentagonal ring having five carbon atoms.
2. Phosphate group: it has three active –OH groups of which two groups are involved in the formation of strand.
3. Nitrogen base: These are cyclic compound named as adenine (A) and guanine (G) called purines and are double ring compounds, whereas thymine (T), cytosine (C), and uracil (U) are called as pyrimidines and are single ring compounds.

DNA (Deoxyribonucleic Acid)

It has deoxyribo sugar. DNA stores the genetic information of an organism as sequence of base A, G, T, and C. uracil base is absent in DNA.

RNA (Ribonucleic Acid)

RNA is produced on DNA template by the process called transcription. It has ribose sugar. RNA is involved in protein synthesis in most of the organisms. mRNA, rRNA and tRNA are three types of RNA.  The uracil base is present in RNA molecule.