FLUORINE

Symbol --- F

Abundance --- 0.065% in the earth’s crust

Allotropes --- alpha, beta

Physical state (STP) --- gas

Colour --- solid [alpha(opaque), beta(transparent)], liquid [bright yellow], gas [pale yellow]

Discovery --- A M Ampere

Atomic no --- 9

Atomic weight --- 18.998

Period --- 2

Group --- 17 or VIIA

Block --- p block

Known isotopes --- ₉F¹⁴, ₉F¹⁵, ₉F¹⁶, ₉F¹⁷, ₉F¹⁸, ₉F¹⁹, ₉F²⁰, ₉F²¹, ₉F²², ₉F²³, ₉F²⁴, ₉F²⁵, ₉F²⁶, ₉F²⁷, ₉F²⁸, ₉F²⁹, ₉F³⁰

Main isotope --- ₉F¹⁹

Isotopic abundance --- ₉F¹⁹ (100%)

Melting Point --- - 219 ⁰C (54 K) (F₂)

Boiling Point --- - 188 ⁰C (85 K) (F₂)

Triple Point --- 54 K, 90 kPa

Critical Temperature --- 144 K

Critical Pressure --- 5.17 MPa

Heat of Fusion --- 0.26 KJ/mol

Heat of Vaporisation --- 6.51 KJ/mol

Molar heat capacity (21 ⁰C) --- C_P [31 J/(mol-K)], C_V [23 J/(mol-K)]

Density --- 1.69 g/L (at STP)

Molar volume --- 0.0112

Electron configuration --- [He] 2s² 2p⁵

Electrons per shell --- 2 (1 st shell), 7 (2 nd shell)

Oxidation state --- -1

Valance --- 1

Electronegativity --- 4.0 (Pauling scale)

Electron affinity --- - 333 KJ/mol

Ionisation energy --- 1680 KJ/mol (1 st), 3375 KJ/mol (2 nd), 6148 KJ/mol (3 rd), 8406 KJ/mol (4 th)

Dissociation enthalpy --- 159 KJ/mol [F₂(gas)]

Covalent radius --- 64 pm

Van der Waals radius --- 135 pm

Atomic radius --- 42 pm

Ionic radius (6 – coord) --- 133 pm

F―F distance --- 143 pm

Natural occurrence --- primordial

Crystal structure --- cubic

Specific heat --- 824 J/(Kg K) (gas)

Thermal conductivity --- 0.025 W/(m K)

E⁰ (V) --- 2.9 [1/2 F₂ + e <==> F^-(aq)]

Magnetic type --- diamagnetic

Lattice angles --- π/2, π/2, π/2

Lattice constants --- 550 pm, 327 pm, 729 pm

Quantum numbers --- ²P_3/2

Neutron cross section --- 9.5 x 10^-3

Neutron mass absorption --- 2 x 10^-5

Refractive index --- 1.0001

SILICONES

A group of organosilicon polymers containing linkages of the type  (---O―Si―O---)  are called silicones. Generally, silicones are three types, such as linear silicones, cyclic silicones and cross-linked silicones.

Preparation of Silicones

Silicones are prepared in three steps, such as preparation of alkyl or aryl chlorosilanes, hydrolysis of alkyl or aryl chlorosilanes to produced silanols and polymerization of silanols.

(1) At first, alkyl or aryl chlorosilanes are prepared by the following way---

(i) When alkyl or aryl chloride (R―Cl) are heated with silicon (Si) at 300 ⁰C in presence of Cu catalyst, mixture of alkyl or aryl chlorosilanes are produced.

2R―Cl + Si ----> RSiCl₃ + R₂SiCl₂ + R₃SiCl

(ii) Reaction of Grignard reagent (R―MgCl) with SiCl₄ produced alkyl or aryl chlorosilanes.

R―MgCl + SiCl₄ ----> RSiCl₃ + MgCl₂

2R―MgCl + SiCl₄ ----> R₂SiCl₂ + 2MgCl₂

3R―MgCl + SiCl₄ ----> R₃SiCl + 3MgCl₂

(2) Hydrolysis of alkyl or aryl chlorosilanes to produced silanols----

When alkyl or aryl chlorosilanes treated with water, silanols are produced.

RSiCl₃ + 3H₂O ----> RSi(OH)₃ + 3HCl

R₂SiCl₂ + 2H₂O ----> R₂Si(OH)₂ + 2HCl

R₃SiCl + H₂O ----> R₃SiOH + HCl

(3) Polymerisation of Silanols---

In the polymerisation process some molecules of H₂O are removed and form various types of silicones such as linear, cyclic or cross linked according to the nature of the alkyl or aryl hydroxy (silanols) derivatives----

(i) Linear silicones---

Polymerisation of dialkyl dihydroxy silane [R₂Si(OH)₂] gives rise to straight chain linear silicone polymers and as an active OH group is left at each end of the chain, polymerisation continues and the chain increases in length. Thus dialkyl dihydroxy silane [R₂Si(OH)₂] is a chain building unit. High polymers are obtained in this way. The structure of linear silicone polymer is as follows---

(ii) Cyclic silicones---

Careful polymerisation of dialkyl dihydroxy silane [R₂Si(OH)₂] can produced cyclic silicone structure containing three, four, five or six silicon (Si) atoms. The structure of cyclic silicone polymer is as follows--

(iii) Cross linked silicones---

Polymerisation of alkyl trihydroxy silane [RSi(OH)₃] gives rise to cross linked two dimensional silicone polymers and as an active OH group is left at each end of the chain, polymerisation continues and chain increases in length. The structure of cross linked silicone polymer is as follows---

Polymerisation of trialkyl monohydroxy silane [R₃SiOH] gives rise to linear straight chain silicone dimer. The structure of silicone dimer is as follows---

Trialkyl monohydroxy silane [R₃SiOH] is used as a chain blocking unit. When some trialkyl monohydroxy silane [R₃SiOH] is mixed with dialkyl dihydroxy silane [R₂Si(OH)₂], the trialkyl monohydroxy silane [R₃SiOH] will block the chain produced by dialkyl dihydroxy silane [R₂Si(OH)₂].

Some Important Silicones

(1) High thermal silicones---

When hydrolysis of alkyl or aryl chlorosilanes is carried out in presence of aluminium halides, titanium halides, aluminium alkoxides or titanium alkoxides two dimensional linear or cyclic high thermal silicone polymer is obtained in which some silicon (Si) atoms are replaced by aluminium (Al) or titanium (Ti) atoms. The presence of Al or Ti atoms in the silicone polymer structure, increases the thermal stability of the polymer. This silicone polymer has exceptionally high thermal stability. The structure of high thermal silicone polymer is as follows---

(2) Silicone oil---

When some trialkyl monohydroxy silane [R₃SiOH] is mixed with dialkyl dihydroxy silane [R₂Si(OH)₂], silicone oil is obtained. It has low temperature coefficient of viscosity, high thermal stability and good insulating properties. The structure of silicone oil is as follows---

(3) Silicone rubbers---

Silicone rubbers are long chain polymer, with some cross linking between the chains. These rubbers retain its elasticity and shape even after vulcanization.

Properties and Uses of Silicones

Silicones are thermally stable, chemically inert, excellent water repellent, good electrical insulator and non toxic. They are resistance to oxidation and most chemicals such as acids, alkalies etc due to their chemical inertness. Their inertness is due to their stable silica like skeleton and high strength of Si―C bonds. They have non stick properties.

They are used in making waterproof cloth, in lubrication, as insulating materials, as antifoams, in cosmetics, as stop cock grease, in electric motor and other electric appliances, as hydraulic fluids, as dielectric fluids etc.

BORAX

Salts of boric acids (H₃BO₃) are called borates. Borax is an important borate. Borax is a sodium salt of tetraboric acid (H₂B₄O₇). Ten molecules of water, as water of crystallization are present in borax compound. So, borax is sodium tetraborate decahydrate [Na₂B₄O₇.10H₂O].

Preparation of Borax

(1) Borax from boric acid (H₃BO₃) ---

(i) Borax is obtained, when boric acid (H₃BO₃) is boiled with sodium carbonate (Na₂CO₃) solution- 

4H₃BO₃ + Na₂CO₃ = Na₂B₄O₇ + CO₂ + 6H₂O

(ii) Borax is obtained, when boric acid (H₃BO₃) is boiled with excess sodium hydroxide (NaOH) solution---

4H₃BO₃ + 2NaOH + 3H₂O = Na₂B₄O₇.10H₂O

(2) Borax from colemanite (2CaO, 3B₂O₃) ---

Borax is obtained, when colemanite (2CaO, 3B₂O₃) is boiled with sodium carbonate (Na₂CO₃) solution ---

2CaO, 3B₂O₃ + 2Na₂CO₃ = Na₂B₄O₇ + 2NaBO₂ + 2CaCO₃

At first, precipitate calcium carbonate (CaCO₃) is filtered out and then concentrated the remaining filtrate. As a result, crystals of borax are deposited. NaBO₂ present in the mother liquor is converted to borax by passing CO₂.

4NaBO₂ + CO₂ = Na₂B₄O₇ + Na₂CO₃

Structure of Borax

The crystal structure study of borax has indicated that, two H₂O molecules participate in the formation of borax anion. So, borax is now represented as----

Na₂[B₄O₅(OH)₄].8H₂O

The anion of borax [B₄O₅(OH)₄]^2- is made up of two trigonal planer BO₃ units and two tetrahedral BO₄ units. The B atom of BO₃ unit is sp² hybridised and each B atom of BO₃ unit forms three B―O sigma(σ) bonds. The B atom of BO₄ unit is sp³ hybridised. one extra electron is present in each BO₄ units and each B atom of BO₄ unit forms four B―O sigma (σ) bonds. Four OH groups linked with four B atoms. A bridge bond is formed among two B atoms and one O atom. So, the structure of the borax anion [B₄O₅(OH)₄]^2- is as follows---

Properties of Borax

White crystalline solid borax exists in three different crystal structure.

(1) Monoclinic or prismatic borax---

The formula of monoclinic or prismatic borax is Na₂B₄O₇.10H₂O, it is the most common form of borax.

(2) Octahedral or jeweller’s borax---

The formula of octahedral or jeweller’s borax is Na₂B₄O₇.5H₂O. The octahedral form of borax (Na₂B₄O_7.5H₂O) is obtained, when monoclinic form of borax (Na₂B₄O₇.10H₂O) is heated above 60⁰C.

(3) Borax glass or anhydrous borax----

The formula of borax glass or anhydrous borax is Na₂B₄O₇. The anhydrous borax (Na₂B₄O₇) is obtained when monoclinic form of borax (Na₂B₄O₇.10H₂O) is heated above its melting point.

In water borax gets hydrolysed, and gives a mixture of strong base NaOH and weak acid H₃BO₃. Since boric acid (H₃BO₃) is weak so, the aqueous solution of borax is alkaline.

Na₂B₄O₇ + 7H₂O <=====> 2NaOH + 4H₃BO₃

On heating borax first swells losing water molecules. On further heating it gives NaBO₂ and B₂O₃. A glassy bead is formed.

Na₂B₄O₇.10H₂O = 2NaBO₂ + B₂O₃ + 10H₂O

Borax bead test-----

When this glassy bead (B₂O₃) is heated strongly with coloured metal salts, specific coloured beads are obtained. This offers a means of identifying certain metal ions like Cu, Co, Cr, Ni, Fe etc.

CuSO₄ = CuO + SO₃

CuO + B₂O₃ = Cu(BO₂)₂

This gives green colour in hot condition and blue colour in cold condition.

When this Cu(BO₂)₂ is again heated in reducing flame it becomes dull red and opaque.

2Cu(BO₂)₂ (Cu = +2) + C ----> 2CuBO₂ (Cu = +1) + B₂O₃ + CO

2CuBO₂ (Cu = +1) + C ----> 2Cu (Cu = 0) + B₂O₃ + CO

Reaction of borax with conc HCl or H₂SO₄ forms boric acid---

Na₂B₄O₇ + 2HCl + 5H₂O = 2NaCl + 4H₃BO₃

Na₂B₄O₇ + H₂SO₄ + 5H₂O = Na₂SO₄ + 4H₃BO₃

When borax is heated with ammonium chloride, boron nitride is formed---

Na₂ [B₄O₅(OH)₄] + 2NH₄Cl ----> 2NaCl + 2BN + B₂O₃ + 6H₂O

Uses of Borax

Borax is used in the manufactured of enamels, washing powders, various types of glasses such as optical and hard glasses. Borax is also used in making antiseptic.

OXYGEN

Symbol --- O

Abundance --- most abundant element, 46% in the earth’s crust, 21% by volume in air, 89% by weight of the water in the oceans.

Allotropes --- atomic oxygen [O(³P)], dioxygen (O₂), ozone (O₃), tetraoxygen (O₄), solid oxygen.

Physical state --- gas

Colour --- colourless gas

Discovery --- C W Scheele

Atomic no --- 8

Atomic weight --- 15.999

Period --- 2

Group --- 16 or VIA

Block --- p block

Known isotopes --- ₈O¹², ₈O¹³, ₈O¹⁴, ₈O¹⁵, ₈O¹⁶, ₈O¹⁷, ₈O¹⁸, ₈O¹⁹, ₈O²⁰, ₈O²¹, ₈O²², ₈O²³, ₈O²⁴

Main isotopes --- ₈O¹⁶, ₈O¹⁷, ₈O¹⁸

Isotopic abundance --- ₈O¹⁶ (99.763%), ₈O¹⁷ (0.037%), ₈O¹⁸ (0.2%)

Melting Point --- - 219 ⁰C (54 K) (dioxygen)

Boiling Point --- - 183 ⁰C (90 K) (dioxygen)

Triple Point --- 54 K, 0.14 kPa

Critical Temperature --- 154 K

Critical Pressure --- 5.04 MPa

Heat of Fusion --- 0.44 KJ/mol (dioxygen)

Heat of Vaporisation --- 6.81 KJ/mol (dioxygen)

ΔH⁰_{(atomization)} --- 247 KJ/mol

Molar heat capacity --- 29.37 J/(mol-K) (dioxygen)

Density --- 1.41 g/L (at STP)

Molar volume --- 0.0111

Electron configuration --- [He] 2s² 2p⁴

Electrons per shell --- 2 (1 st shell), 6 (2 nd shell)

Oxidation state --- -2, -1

Valance --- 2

Electronegativity --- 3.44 (Pauling scale)

Electron affinity --- 1.41 KJ/mol

Ionisation energy --- 1314 KJ/mol (1 st), 3388 KJ/mol (2 nd), 5300.3 KJ/mol (3 rd), 7469.1 KJ/mol (4 th)

Covalent radius --- 66 pm

Van der Waals radius --- 152 pm

Atomic radius --- 48 pm

Natural occurrence --- primordial

Crystal structure --- cubic

Specific heat --- 918.5 J/(Kg K) (gas)

Thermal conductivity --- 0.026 W/(m K)

Speed of sound --- 330 m/s (gas)

Magnetic type --- paramagnetic

Mass magnetic susceptibility --- 1.33 x 10^-6 m³/Kg

Molar magnetic susceptibility --- 4.27 x 10^-8 m³/mol

Volume magnetic susceptibility --- 1.9 x 10^-6

Lattice angles --- π/2, 2.31, π/2

Lattice constants --- 540.1 pm, 342.8 pm, 508.5 pm

Quantum numbers --- ³P₂

Neutron cross section --- 2.8 x 10^-4

Neutron mass absorption --- 1 x 10^-6

Refractive index --- 1.0002

POLYTHENE or POLYETHYLENE

Polythene or polyethylene is very useful and one of the most common polymers today. Polythene or polyethylene is prepared from pure ethylene (pure ethylene obtained from petroleum) by polymerization process either by high pressure method or by low pressure method. Polythene or polyethylene which is manufactured by high pressure method possesses a low density, hence this type of polythene or polyethylene is known as high pressure polythene or low density polythene. Polythene or polyethylene which is manufactured by low pressure method possesses a high density, hence this type of polythene or polyethylene is known as low pressure polythene or high density polythene.

High Pressure Method

When polythene or polyethylene is synthesized by high pressure method a free radical yielding catalyst such as oxygen or peroxide is required.

Ethylene with highly pure quality is polymerized at a pressure of 1000 – 1500 atm and at temperature of 250 ⁰C in the presence of a free radical yielding catalyst. From the reactor, the molten liquid passes to a separator. In the separator the unreacted ethylene is removed and recycled. So, now in the separator molten liquid is water white polythene or polyethylene. This can be extruded, chilled and solidified, chopped and stored. By adding fillers and colouring matter to the molten polymer, moulding powder can be prepared.

Since polythene or polyethylene prepared by high pressure method possesses a low density, so this type of polythene or polyethylene are highly branched, consists of several short and long branches, as shown in the following structure----

High pressure polythene or low-density polythene is extremely poor conductor of electricity, chemically inert, tough, flexible over a wide range of temperature. This type of polythene or polyethylene is not attacked by acids, alkalies or oil.

High pressure polythene or low density polythene is used for the fabrication of king toys, making pipes, making containers, wires and cable insulation, in films, in packings, articles of domestic use, making bottles.

Low Pressure Method

When polythene or polyethylene is synthesized by low pressure method a metal derived catalyst is required. Some examples of metal derived catalyst are titanium tetrachloride in a hexane solution of aluminium triethyl, chromium oxide on a silica alumina support etc.

Ethylene with highly pure quality and cyclohexane solvent along with a suitable metal derived catalyst are fed to a reactor. Here cyclohexane solvent serves for several purpose such as----

Cyclohexane solvent acts as a medium for dissipating the heat of reaction.

Cyclohexane solvent controls the rate of consumption of ethylene.

Cyclohexane solvent protects the growing polymer from chain breaks.

In the reactor under 35 atm pressure and at a temperature of 60 – 200 ⁰C ethylene is polymerized. From the reactor, the molten liquid passes to a flash drum. In the drum excess cyclohexane and unreacted ethylene are removed. The polymer produced due to polymerization of ethylene is then centrifuged and filtered. The polymer which is ash free thus obtained, is precipitated from the solution in a stripper to get a slurry. By floatation, the slurry is separated from water. It is then dried and finished.

Since polythene or polyethylene prepared by low pressure method possesses a high density, so this type of polythene or polyethylene molecules contains linear unbranched chains. These chains can be close packed in the solid state. Due to this close packing, this type of polythene or polyethylene has high density.

Low pressure polythene or high density polythene is more stronger, chemically more inert, more stiffer and harder than low density polythene.

High density polythene possesses high softening temperature and greater tensile strength.

Low pressure polythene or high density polythene is used for making toys, bottles, containers etc. This polythene is also used in the injection moulding of house wares.

 

PAINTS and PIGMENTS

Paints are liquid substances, which hold solid colouring material suspension, known as pigments. These stable mechanical mixtures can be applied evenly to a surface for protective purpose, decorative purpose or both.

Essential ingredients of paints are---

Pigments

Various inorganic or organic insoluble substances which are widely used in surface coatings are known as pigments. Pigments are naturally occurring or manufactured and the colour of the paint depends upon the colour of the pigments.

The important properties of pigments are---

(1)         Good covering power.

(2)         Good mixing ability with oil.

(3)         Opacity

(4)         Chemical inertness of pigments.

(5)         Toxicity level of pigments are very low or nil.

(6)         High hiding power.

(7)         High limiting strength.

(8)         Pigments reflect the destructive UV light and protect the film.  

Extenders or Fillers

Extenders or fillers are inert solid substances. Some examples of extenders or fillers are talc, BaSO₄, china clay, asbestos etc. In order to decrease the cost of the paints and to supplement the pigments in increasing the covering and weathering power of the film, the extenders or fillers are added to the paint. Extenders or fillers improve the consistency, levelling, durability and setting of the paints.

Driers

In order to accelerate the drying of the film through oxidation and polymerization, certain driers also been used in the paint. The polymerization of the unsaturated drying oils occurs by a reaction mechanism which involves peroxide intermediate. Due to catalytic activity of the drier they act as a catalyst and promoters in the oxidation polymerization process. Driers are generally mixed with hot boiled linseed oil. Driers dissolve in the hot oil and they reduced the drying time. Some examples of driers are Co, Mn, Pb, cobalt linoleates, cobalt tungstates, MnO₂, litharge, lead acetate, manganese acetate etc.

Thinners or Diluents

In order to dissolve film forming material and to thin concentrated paints for better handling, thinners or diluents is also added to the paints. Some examples of thinners or diluents are petrol, benzene, naphtha, rosin spirit etc.

Film Forming Materials

The film forming materials acts as carriers for the pigments.

Antiskinning Agents

Certain antiskinning agents such as polyhydroxy phenols are added to the paint in order to prevent gelting and skinning of the finished product.

Plasticizer

Plasticizers are added to the paint, in order to reduce certain aspects of cracking in paints.

Resins

A variety of resins are also added to the paints.

Classification of pigments

According to the colour of the pigments, they are classified in the following types---

(A) White Pigments------

(i) White lead [Pb(OH)₂.2PbCO₃]

(ii) Zinc oxide [ZnO]

(iii) Titanium dioxide [TiO₂]

(iv) Lithopone [BaSO₄ + ZnS]

(B) Blue Pigments----

(i) Ultramarine

(ii) Cobalt blue

(iii) Iron blue

(C) Red Pigments----

(i) Red lead [Pb₃O₄]

(ii) Cadmipone [CdS + BaSO₄]

(iii) Iron oxide [Fe₂O₃]

(iv) Chrome red [Pb(OH)₂.PbCrO₄]

(D) Black Pigments-----

(i) Carbon black

(ii) Furnace black

(iii) Lamp black

(E) Green Pigments----

(i) Chrome green [Cr₂O₃]

(ii) Malachit green [Cu(OH)₂.CuCO₃]

(iii) Rinman’s green [CoO.ZnO]

(F) Orange Pigments----

(i) Cadmium orange

(ii) Basic lead chromate

(G) Yellow Pigments----

(i) Lead chromates

(ii) Zinc chromates

(iii) Litharge

(iv) Ocher [A naturally occurring pigment]

(H) Brown Pigments----

(i) Burnt umber

(ii) Burnt sienna

(I) Metallics Pigments----

(i) Zinc dust

(ii) Copper powder

(J) Metal Protective Pigments----

(i) Zinc and basic lead

(ii) Red lead

Due to durability and colouring power of toners (insoluble organic dye), they are also used directly as pigments.

Lakes are organic dyes on an inorganic absorbent, have also been used as pigments.

Requisites of a good paint

(i) Paint should be resistant to heat and light.

(ii) Due to small change of temperature, the colour of paint should not fade.

(iii) Due to exposing to light, the colour of paint should not fade.

(iv) Paint should be resistant to the corrosive action of acids and bases.