Trends in chemical reactivity of group 13 elements

The important trends observed in the chemical behavior of group 13 elements are

1. Group 13 elements form hydrides of the type MH3. Thermal stability of hydrides decreases as we move down the group. Hydrides act as weak lewis acids. Boron forms a number of hydrides known as boranes. The important series among boranes are nido-boranes (BnHn+4) and arachno-boranes (BnHn+6). Aluminium and Galium can form tetra hydrido anions (MH4-).[LiAlH4] is an example for this and is a good reducing agent used in organic synthesis.

2. The elements of group 13 form trihalides of the type MX3. The trihalides are strong Lewis acids. The flurides are ionic and have high melting points. The chlorides, bromides and iodides are covalent compounds with low melting points. Halides can exist in dimeric form with halogen bridges.

3. All the elements of group 13 form oxides with formula M2O3 and hydroxides of the type M(OH)3. Basic character of oxides and hydroxides increases as we move down the group.

4. Due to the presence of d-orbitals Aluminum, Gallium, Indium and Thallium can form octahedral complexes (eg: [AlF3]3-) and octahedral aqua ions, [M(OH2)6]3+. Because of small size and increased nuclear charge, many salts like halides, sulphates, nitrates and perchlorates exist as hydrates. Aluminum sulphate forms double salts with other sulphates of monovalent metals and are called alums, having general formula MAl(SO4)2.12H2O, where M is univalent cation like Na+ or K+. Alums are used for softening hard water and used as mordant.

Group 13 elements and their nature

1. Boron

Oxide - B2O3
Hydroxide - B(OH)3
Nature - Weakly acidic

2. Aluminum

Oxide - Al2O3
Hydroxide - Al(OH)3
Nature - Amphoteric

3. Gallium

Oxide - Ga2O3
Hydroxide - Ga(OH)3
Nature - Amphoteric

4. Indium

Oxide - In2O3
Hydroxide - In(OH)3
Nature - Basic

Related chemistry article Trends in chemical properties of group 17 elements

Chemical Reactivity in Group 17 elements

Trends of chemical properties in group 17 elements

1. Oxidizing property of halogens

Group 17 elements are highly electronegative and hence they have strong tendency to accept electrons. Thus halogens act as strong oxidizing agents. F2 is the strongest oxidizing halogen. A halogen can oxidizes halide ions of higher atomic number.

F2 + 2X- ----------> 2F- + X2

[X = chlorine (Cl), Bromine (Br) or Iodine (I)]

The oxidising ability of halogens decreases as we go down the Group.

2. Formation of Halides

Halogens combine with metals, nonmetals and even noble gases to form halides. Metal halides are ionic and their ionic character decreases as M-F > M-Cl > M-Br > M-I

Halogens combine with nonmetals and form covalent halides whose bond strength decreases as M-F > M-Cl > M-Br > M-I

3. Hydrides (Hydrogen halides)

Halogens combine with hydrogen to form covalent halides of the type HX and are regarded as hydrides. Their acidic and reducing character increase as we go down the group as HF < H-Cl < HBr < HI
The thermal stability decreases down the group HF > HCl > HBr > HI

Aqueous solution of hydrogen halides are known as hydrohalic acids.
Hydrogen chloride is prepared by heating sodium chloride with concentrated H2SO4.

2NaCl + H2SO4 ----------> Na2SO4 + 2HCl

Related article Trends in group 13 elements

Williamson's synthesis of Ethers

Preparation of ethers using sodium alkoxide

This is an important laboratory method for the preparation of symmetrical and unsymmetrical ethers. In this method, ethers are prepared by heating an alkyl halide with sodium alkoxide.

Ethers containing substituted alkyl groups (secondary or tertiary) may also be prepared by this method. The reaction involves a nucleophilic substitution of halide ion by an alkoxide ion.

Thus, good results are obtained if the alkyl halide is primary. If a tertiary alkyl halide is used, an alkene is the only reaction product and no ether is formed. For example, the reaction of CH3CONa with (CH3)3 C-Br gives exclusively 2 -methyl propene.

It is because alkoxides are not only nucleophiles but also strong bases. They react with alkyl halides leading to elimination reactions.

Since halogen attached to the benzene ring is not reactive, in order to prepare an alkyl aryl ether, a mixture of alkyl halide and sodium phenoxide must be heated.

For example, ethyl phenyl ether is obtained by heating a mixture of ethyl iodide and sodium phenoxide.

Preparation of Ethers

Preparation of Ethers by Dehydration of Alcohols

When excess of a primary alcohol is heated with protonic acids like conc.H2SO4 or H3PO4 at 413 K , it undergoes dehydration to form an ether.

2R - OH (Alcohol) -----(conc.H2SO4, 413K)-----> R-O-R (Ether) + H2O

2C2H5 OH (Ethanol)-----(conc.H2SO4, 413K)-----> C2H5-O-C2H5 (Diethyl ether) + H2O

But this reaction cannot be used for the preparation of unsymmetrical ethers.

The formation of reaction product depends on the reaction conditions. At high temperature, if excess of acid is used dehydration occurs in a different way to form an alkene. For example, ethanol when heated with conc.H2SO4 at 440K undergoes dehydration to give ethylene.

CH3 CH2 OH -----(conc.H2SO4, 413K)-----> CH2 = CH2 + H2O

The dehydration of secondary and tertiary alcohols to the corresponding ethers is unsuccessful as alkenes are formed easily in these reactions.

The dehydration of alcohols can also be brought about by passing the vapours of the alcohol under pressure over a heated catalyst like alumina or thoria at 523 K.

2C2H5 OH (Ethanol) -----(conc.H2SO4, 523K)-----> C2H5-O-C2H5 (Diethyl ether) + H2O

For preparation of Phenol visit

Kolbe's reaction of phenol

When sodium salt of phenol (sodium phenoxide) is heated at about 400 K with carbon dioxide gas under a pressure of about 4-7 atmospheres and the product acidified, ortho hydroxy benzoic acid (salicylic acid) is formed as the main product.

Kolbe's reaction phenol

Saliccylic acid on actylation using acetic anhydride gives aspirin (acetyl salicylic acid).

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Fries rearrangement: Reaction of phenol
Coupling Reaction of  Phenol
Reimer-Tiemann reaction of phenol

Nitration: reaction of Phenol

Phenol reacts with dilute nitric acid at low temperature (298 k) to yield a mixture of ortho nitro phenl (15 %) and para nitrophenol (30-40 %).

The ortho and para isomers of nitrophenol can be separated by steam distilation. O-Nitrophenol is steam volatile due to intra molecular hydrogen bonding while p-nitrophenol is less volatile due to intermolecular hydrogen bonding which causes the association of molecules.

But, when nitration is carried out using concentrated nitric acid, phenol is converted to 2,4,6-trinitrophenol known as picric acid. In this reaction nitration is accompanied by oxidation of phenol.

Preparation of Picric acid

Industrially, picric acid is prepared by treating phenol, first with concentrated H2SO4 which converts it to phenol-2,4-disulphuric acid. This yields picric acid on treating it with conc. HNO3

Fries rearrangement: Reaction of phenol

Esters of phenols yield phenolic ketones on treatment with anhydrous aluminum chloride. This intermolecular rearrangement is called Fries rearrangement. This reaction involves the migration of an acyl group from phenolic oxygen to ortho and para positions of the aromatic ring with respect to the hydroxyl group. For example, phenyl ethanoate yields ortho- and para- hydroxy aceto phenones.

fries rearrangement reaction of phenol

Fries rearrangement is considered better than direct acylation as the yield is good.

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Kolbe's Reaction of Phenol
Coupling Reaction of  Phenol
Reimer-Tiemann reaction of phenol

Coupling Reaction of Phenol

When an ice cold solution of phenol is treated with an ice cold solution of benzene diazonium chloride in mildly alkaline medium p_hydroxy azo benzene (Azo dye) is formed. This reaction is called coupling reaction.

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Kolbe's Reaction of Phenol
Fries rearrangement: Reaction of phenol
Reimer-Tiemann reaction of phenol

Group 18 elements properties

Group 18 consists of the elements, helium, neon, argon, krypton, xenon, and radon, which are collectively known as noble gases. Due to their chemical inactivity they are also called inert gases.

Occurrence and isolation
Atmospheric air is the major source of noble gases. Radon is not found in atmosphere and is obtained as thee decay product of 226Ra. The total abundance of noble gases in dry air is approximately 1%.

Neon, Argon, Krypton and Xenon are obtained by the liquefaction of dry air and separation of its constituents by fractional distillation. Helium is isolated from natural gas. When natural gas is compressed and liquefied, Helium remains along with unliquefied gas, which contains 2% nitrogen as impurity. N2 is removed by adsorption on charcoal at – 1900C.

Atomic and physical properties

Electronic configuration
Except Helium, all other noble gases have ns2np6 configuration. The electronic configuration of He is IS2. Due to this stable electronic configuration, they have less tendency to take part of in chemical reactions.

Atomic radius
The atomic radii of noble gases are taken as van der Walls radius. As we move down the group atomic radii increases due to the increase in number of shells.

Ionization energy
Group 18 elements have highest ionization energy in their respective periods due to their stable noble gas configuration. Thus is one of the reasons for their less reactivity. Ionization energy decreases on moving down the group due to increase in atomic size.

Electron affinity
Due to stable closed shell configuration ns2 np6, noble gases have no tendency to accept additional electron. Therefore electron affinity of noble gases is almost equal to zero. This also makes them reluctant towards chemical reaction.

The tendency for liquefaction of noble gases increases on moving down the group due to increase in vander Waal's force with increase in size of atom.

Uses Of Noble Gases

The important uses of Noble gases are

1. Helium is used for filling balloons and airships.

2. Helium is used for producing inert atmosphere in certain processes such as metallurgical operations.

3. Liquid Helium is used as cryogenic agent for carrying out various experiments at low temperatures.

4. Argon is used to provide inert atmosphere in high temperature metallurgical operation and used for filling electric bulbs.

5. Neon is used in discharge tubes and fluorescent bulb for advertisement display purpose.

6. Radon is used in radio therapy for the treatment of cancer.

7. Xenon and Krypton has no significant uses except that are used in certain light bulbs for special purpose.

Related article P - block elements

Oxyacids of chlorine

The oxyacids of chlorine are HCLO (Hypochlorous acid), HCLO2 (Chlorous acid), HCLO3 (Chloric acid) and HCLO4 (Perchloric acid).

1. Hypochloric acid or chloric(1)acid (HCLO)

It is formed by passing chlorine gas through water.

Cl2(g) + H2O (l) ----------> Na2SO4(aq) + 2 HCl (aq)

2. Chlorous acid or chloric (3)acid (HClO2)

It is prepared by treating barium chlorate with sulphuric acid.

Ba(ClO2)2 + H2SO4 -----------> 2HClO2 + BaSO4

3. Chloric acid or chloric(5)acid (HClO4)

Perchloric acid is prepared by treating barium perchlorate with sulphuric acid.

Ba(ClO4)2 + H2SO4 ------------> 2HClO3 + BaSO4

4. Perchloric acid or chloric (6) acid

Perchloric acid is prepared by treating barium perchlorate with sulphuric acid.

Ba(ClO4)2 + H2SO4 -----------> 2HClO4 + BaSO4

For List of oxyacids visit (picture) oxyacids of chlorine

For Other examples of oxyacid visit oxyacids of phosphorous

Imperfections in solids

A perfectly ordered crystal can exist only at absolute zero. Above this temperature some departure from ordered arrangement occurs. These are called imperfection or defects.Crystals contain a group of micro crystals with irregularities at crystals boundaries or grain boundaries. These are called lattice defects. The irregularities may also be present at several lattice points. They are called points defects.
Point defects
These are defects localized at lattice points or at voids. Thus 1 cm3 of a crystal of NaCl with 10^22 Na+ and 10^22Cl- ions has 10^6 vacant Na+ lattice positions at room temperature. Metallic crystals also contain such vacant lattice positions due to missing of metal atom in the lattice. The lattice positions from which lattice atoms or ions are missing are called vacancies. Thus ionic crystals have cation and anion vacancies. Point defects can also arise due to various other factors and it is convenient to classify them as follows.
1. Stoichiometric defects
2. NonStoichiometric defects
3. Impurity defects
1. Stoichiometric defects
They are defects, which do not affect the stoichiometry or formula of the compound.These are further divided in to two.
a. Schottky defects
These are defects in ionic crystals, which arise due to missing of equal amounts of cations and anions. A cation vacancy is compensated by an anion vacancy of equal charge. Thus NaCl,KCl,CsCl,KBr etc contain this defect.
The empirical formula in unaffected but the density of the crystal is lowered and electrical conductance is increased by such defects. These defects are predominant in ionic crystals with cation and anion of nearly equal size.

b. Frenkel defects
In ionic crystal such as those like AgCl the cations(Ag+) are quite small compared to the anions(Cl-). Some cations move away from lattice positions giving rise to a cation vacancy. The cation now occupies an interstitial void such as octahedral or tetrahedral voids. Such defects are termed Frankel defects. Here the empirical formula and the density are unaffected but conductance increases.
2. Non Stoichiometric point defects
These are point defects, which affect the formula of the compound. They are of two types
a. metal deficiency defects
b. metal excess defect

a. Metal deficiency defect
Ferrous oxide is expected to have the formula FeO. But the actual formula is in the range Fe0.95O. The metal deficiency is due to missing of some Fe2+ ions from the lattice. To maintain electrical neutrality double the number of Fe2+ acquire higher oxidation state of Fe3+.
b. Metal excess defects
Such crystals have higher proportion of cation than required by stoichiometric formula. Thus NaCl crystal heated in Na vapour condense on the crystal surface and ionize to Na+ ion and electron both Na+ and electron diffuse in to the crystal lattice. Na+ ion occupy a cation vacancy and electron in a anion vacancy. The anion vacancy which has trapped the electron is called an F center or colour center.
3. Impurity defects
Point defects can be introduced in solids by addition of impurities. Thus if NaCl crystals are grown in a saturated solution of NaCl containing some SrCl2. To maintain electrical neutrality for every Na+ displaced by Sr2+ one Na+ will be missing from the lattice.

Imperfection in solids in pdf format

Reimer-Tiemann reaction of phenol

When phenol is heated with chloroform in presence of aqueous alkali (NaOH) at 340 K followed by hydrolysis of the resulting product a -CHO group is introduced at ortho position of benzene ring to form a phenolic aldehyde known as salicylaldehyde (O- hydroxy benzaldehyde) as the main product. A small amount of the para isomer is also obtained. This reaction is known as Reimer - Tiemann reaction.

Instead of chloroform, if carbon tetrachloride is used in the above reaction salicylic acid (O- hydroxy benzoic acid) is obtained as the major product.

reimer tiemann-phenol-reaction

Test for Phenol

Reaction of Phenol with neutral Ferric Chloride

Phenol reacts with neutral ferric chloride to give a violet coloured water soluble complex.

C6H5OH + FeCl3 --------------> [Fe(OC6H5)6]3- + 3H+ + 3HCl

The complex formed is a coordination compound in which iron is hexacovalent. In fact, all compounds, whether aliphatic or aromatic containing the enol group (C=C-OH) but unlike alcohol give characteristics colours with neutral FeCl3. Different phenols give different colour. This reaction forms the basis of group test for the enolic grouping and may also be used to disitnguish between different phenols on the basis of the colour obtained.

Physical properties of alcohols and phenols

Alcohols and phenols consist of two parts, an alkyl/aryl group and a hydroxyl group. The properties of alcohols and phenols are due to the OH group.The alkyl and aryl groups modify these properties.
The boiling points of alcohols and phenols increase with increase in the number of carbon atoms. This is due to increase in van der Waals forces. In alcohols, the boiling points decrease with increase in branching. The reason is that when branching increases, vander Waals forces decreases due to decrease in surface area.
The –OH group in alcohols and phenols contain a hydrogen bonded to an electronegative oxygen atom. Therefore, it is capable of forming hydrogen bond.
Alcohols and phenols have higher boiling points than the corresponding other classes of compounds namely hydrocarbons, ether and halo alkanes/haloarenes of comparable molecular masses due to the presence of intermolecular hydrogen bonding in them.
The solubility of alcohols and phenols in water is due to their ability to form hydrogen bonds with water molecules. The solubility decreases with increase in size of the hydrophobic group (R).

Extraction of iron

 Iron is extracted from its oxide ores. The ores are crushed and concentrated by gravity method. Magnetite is further concentrated by magnetic method. The concentrated ore is calcined to remove volatile impurities and make the ore porous. The calcined ore contains SiO2 as the chief impurity. It is mixed with lime stone (CaCO3) as flux and coke as reducing agent and the mixture is charged into a blast furnace (a very tall steel tower lined inside with fire bricks). The charge is heated by a hot blast of air preheated at 1000 K blown in through narrow pipes (tuyers) at the base of the furnace. Here coke burns producing heat and temperature rise to 2100 K.

C + O2 --------------> CO2 + heat

The temperature falls to 500 K towards the top of the furnace due to the endothermic reaction.

CO2 + C ---------------> 2CO - heat

Carbon monoxide reduces iron oxide to iron in the middle and upper regions of the furnace.

3Fe2O3 + CO -----------------> 2Fe3O4 + CO2

Fe3O4 + 4CO -----------------> 3Fe + 4 CO2

The molten iron formed at the lowest zone dissolve impurities like C, Si, Mn, S, P etc. and gets collected in the hearth of the furnace. Above 1000 K limestone decomposes to CaO, which combine with silica in the hot regions of the furnace to form a slag, which gets collected over molten iron.

CaCO3 --------------> CaO + CO2

CaO + SiO2 --------------> CaSiO3 (slag)

The molten iron and the molten slag are removed through their respective tap holes. The iron from blast furnace contains about 4% carbon and one to two percent other impurities like Mn, Si, S and P. It is called pig iron. Pig iron is remelted and cast into moulds, this is known as cast iron.

 Wrought Iron
This is the purest form of iron. it is obtained by oxidising the impurities of cast iron by heating with haematite. Carbon is oxidised to CO. Si, P and Mn are also oxidised and form a slag which is removed by passing through rollers. Wrought iron is 99.5% pure. It is malleable and ductile and used for making chains, bolts, nails etc.

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Extraction of Sodium

 As sodium is a highly electro positive metal it cannot be prepared by the usual methods of reduction. The metal is extracted by the electrolysis of a molten mixture of NaCl, CaCl2 and KF in a Downs cell at 600 degree Celsius. The cell has a graphite anode and a circular iron cathode, both covered and with proper outlets. Chlorine liberated at the cathode rises up through a pipe and gets collected in a receiver in the molten state.

NaCl ------> Na+ + Cl-

Na+ + e- -------> Na (At cathode)

 2Cl- --------> Cl2 + 2e- (At anode)

The electrolysis of NaCl presents some difficulties. The fusion temperature of pure NaCl is 803 degree celsius. At this temperature both Na and Cl2 are highly corrosive. Addition of CClCl2 and KF reduce the fusion temperature to 600 degree celsius.

Did you Know how the extraction of aluminum is done ? visit for more details extraction of aluminum