thepblockelements.ppt

THE P BLOCK ELEMENTS

There are 6 groups (13-18) Boron Family Carbon Family Nitrogen Family Oxygen family (Chalcogens) Halogen Family Noble Gas Family

The elements in which the last electron enters in the outermost p orbital

GENERAL ELECTRONIC CONFIGURATION AND OXIDATION STATES OF P-BLOCK ELEMENTS

REASON FOR ANOMALOUS BEHAVOUR OF FIRST MEMBER FROM OTHERS

Small size

High electronegativityNon-availabilty of d- orbitals to expand valency

GROUP 13 ELEMENTSBORON FAMILY

ELECTRONIC CONFIGURATION

Name Symbol

electron configuration

Boron B [He]2s22p1

Aluminium Al [Ne]3s23p1

Gallium Ga [Ar]3d104s2 4p1

Indium In [Kr]4d105s2 5p1

Thallium Tl [Xe]4f14 5d106s2 6p1

•General electronic configuration ns2 np1

•Stable Oxidation state +3 decreases as we move down the group due to inert pair effect

ATOMIC RADII Atomic Radii *(pm)

B (85)Al 143

Ga 135

In 167

Tl 170On moving down the group atomic radius is expected to

increase.

However, Atomic radius of Ga is less than that of Al. due to the poor screening effect of intervening d orbitals

IONIZATION ENTHALPY

The ionisation enthalpy values do not decrease smoothly down the group.

Variation can be explained on the basis of poor screening effect of d and f electrons.

ELECTRONEGATIVITY

Down the group, electro negativity first decreases from B to Al and then increases marginally because of the discrepancies in atomic size of the elements.

B 2.0Al 1.5

Ga 1.6

In 1.7

Tl 1.8

PHYSICAL PROPERTIES

Boron hard black coloured high melting non metallic solid

Others are soft metals with low melting point and high electrical conductivity.

Density of the elements increases down the group from boron to thallium.

OXIDATION STATE AND TRENDS IN CHEMICAL REACTIVITY

Except B all other are metals

Boron due to small size forms covalent compounds.

Aluminum (Al) forms +3 cations.

Gallium (Ga), indium (In), and thallium (Tl) all form +3 cations, but also +1 cations,

The relative stability of +1 oxidation state progressively increases as we move down in the group due to inert pair effect

Al<Ga<In<Tl.

INERT PAIR EFFECT

Reluctance of ns2 electrons to take part in bonding due to the poor shielding effect of intervening d and f orbitals on moving down the group

ELECTRON DEFICIENT CHARACTER

In +3 state they form electron deficient compounds

e.gBF3

so they behave as Lewis acids. Acidity decreases with the increase in the size

down the group. e.g BCl3 easily combine ammonia to form BCl3:NH3.

AlCl3 achieves stability by forming a dimer

REACTIVITY TOWARDS AIR

Boron is un reactive in crystalline form. Aluminium forms a very thin oxide layer on the

surface which protects the metal from further attack.

Amorphous boron and aluminium metal on heating in air form B2O3 and Al2O3 respectively.

Basic nature of these oxides increases down the group.

Boron trioxide is acidic ,Aluminium and gallium oxides are amphoteric and those of indium and thallium are basic in their properties.

REACTIVITY TOWARDS NITROGEN

Only B and Al forms nitrides at high temperature

REACTIVITY TOWARDS ACIDS AND ALKALIES

B does not react with acids and alkalies even at moderate temperature

Al shows amphoteric character. Aluminium dissolves in dilute acids and alkalies and

liberates hydrogen.

In concentrated HNO3 Al becomes passive by forming a protective oxide layer on the surface.

REACTIVITY TOWARDS HALOGENS

These elements react with halogens to form tri halides (except Tl I3).

2E(s) + 3 X2 (g) → 2EX3 (s) (X = F, Cl, Br, I)

IMPORTANT TRENDS ANDANOMALOUS PROPERTIES OF

BORON The tri-halides(except F-) being covalent in nature are

hydrolysed in water. Species like tetrahedral [M(OH)4]– and octahedral

[M(H2O)6]3+, except in boron, exist in aqueous medium. The monomeric trihalides, being electron deficient, are

strong Lewis acids. Eg: F3B + :NH3 → F3B ←NH3

the maximum covalence of B is 4. Al and other elements, the maximum covalence can be expected beyond 4.

Most of the other metal halides (e.g., AlCl3) are dimerised through halogen bridging (e.g., Al2Cl6).

SOME IMPORTANT COMPOUNDS OF

BORON

BORAX (NA2B4O7⋅10H2O)white crystalline solid

it actually consists of four units and there fore the correct formula is Na2[B4O5 (OH)4].8H2O.

Borax dissolves in water to give an alkaline solution.Na2B4O7 + 7H2O → 2NaOH + 4H3BO3

Orthoboric acidOn heating, borax first loses water molecules and swells up. On further heating itturns into a transparent liquid, which solidifies into glass like material known as borax bead.

The metaborates of many transition metals have characteristic colours and, therefore,

borax bead test can be used to identify them in the laboratory. Eg: CoO gives blue coloured Co(BO2)2 bead

ORTHOBORIC ACID (, H3BO3 )Preparation Acidification of aqueous solution of borax.

Na2B4O7 + 2HCl + 5H2O → 2NaCl + 4B(OH)3

It is also formed by the hydrolysis of most boron compounds (halides, hydrides, etc)

Properties (Physical)

white crystalline solid, with soapy touch. sparingly soluble in water but highly soluble in hot water.

Properties (Chemical)

weak monobasic lewis acid

On heating, above 370K forms meta boric acid which on further heating yields boric oxide,

STRUCTURE It has planar layer structure in which BO3 units are joined by hydrogen bonds (dotted

line) as shown below

DIBORANE ( B2H6 )Preparation By treating BF3 with LiAlH4 in diethyl ether.

By the oxidation of sodium borohydride with iodine.(Laboratory method)

By the reaction of BF3 with sodium hydride.( Industrial method)

Properties (Physical)

colourless, highly toxic gas with a b.p. of 180 K. catches fire spontaneously upon exposure to air

Properties (Chemical)

It burns in oxygen releasing an enormous amount of energy.

DIBORANE ( B2H6 ) Properties (Chemical)

Boranes are hydrolysed by water to give boric acid.

Diborane undergoes cleavage reactions with Lewis bases(L) to give borane adducts,BH3⋅L

Reaction of ammonia with diborane gives initially B2H6.2NH3 which on further heating gives borazine, B3N3H6 known as “inorganic Benzene”

Reaction with MH diethyl ether medium diborane forms borohydrides which acts as good organic reducing agents

Eg:NaBH4

DIBORANE ( B2H6 )

Each B atom uses sp3 hybrids for bonding. Out of the four sp3 hybrids on each B atom, one

is without an electron shown in broken lines. The terminal B-H bonds are normal 2-centre-2-

electron bonds The two bridge bonds are 3-centre-2-electron

bonds.The 3-centre-2-electron bridge bonds are also

referred to as banana bonds.

STRUCTURE OF DIBORANE, B2H6

three –center bond

DIBORANE ( B2H6 ) STRUCTURE CONTD…….

(B-H-B) bonds are special type and known as Three centre two electron bond or Banana bond

BONDING IN AL2CL6

USES OF BORON AND ITS COMPOUNDS Boron fibres are used in making bullet-proof vest

and light composite material for aircraft. The boron-10 (10B) isotopes(metal borides} are

used in nuclear industry as protective shields and control rods.

borax and boric acid is used in the manufacture of heat resistant glasses

(e.g., Pyrex), glass-wool and fibre glass. Borax is also used as a flux for soldering metals,

for heat, scratch and stain resistant glazed coating to earthen wares

Borax is used as a constituent of medicinal soaps. An aqueous solution of orthoboric acid is generally used as a mild antiseptic.

USES OF ALUMINIUM AND ITS COMPOUNDS

Aluminium is used extensively in industry and every day life. It forms alloys with Cu, Mn, Mg, Si and Zn.

Aluminium and its alloys can be given shapes of pipe, tubes , rods, wires, plates or foils and, therefore, find uses inpacking, utensilmaking, construction, aeroplane and transportationindustry.

The use of aluminium and its compounds for domestic purposes is now reduced considerably because of their toxic nature.

GROUP 14 ELEMENTS

CARBON FAMILY

ELECTRONIC CONFIGURATION

•General electronic configuration ns2 np2

Symbol Electronic configuration

6C  [ He ]2S2 2P2

14Si  [ Ne ] 2S2 3P2

32Ge   [ Ar ] 3d10 4S2 4P2

50Sn   [ Kr ] 4d10 5S2 5P2

82Pb   [ Xe ] 4f14 5d10 6S2 6P2

ATOMIC RADII Atomic Radii *(pm)

On moving down the group atomic radius and ionic radius increases

CSi Ge Sn Pb

Atomic radius (pm) 77 118 122 140 146Ionic radius (pm) M4+ - 40 53 69 78Ionic radius (pm) M2+ - 73 118 119

IONIZATION ENTHALPY

The IE1 of group 14 members is higher than the corresponding members of group 13.

General the ionisation enthalpy decreases down the group.

Small decrease in ΔiH from Si to Ge to Sn and slight increase in ΔiH from Sn to Pb is the consequence of poor shielding effect of intervening d and f orbitals and increase in size of the atom.

ELECTRONEGATIVITY

Due to small size, the elements of this group are slightly more electronegative than group13 elements.

The electronegativity values for elements from Si to Pb are almost the same.

  C Si Ge Sn Pb

2.5 1.8 1.8 1.8 1.9

PHYSICAL PROPERTIES

All group 14 members are solids. Melting points and boiling points 14

elements are much higher than those of corresponding elements of group 13.

MEMBER CHARACTER

CARBON NON METAL

SILICON NON METAL

GERMANIUM METALLOID

TIN Soft METAL

LEAD Soft METAL

OXIDATION STATE AND TRENDS IN CHEMICAL REACTIVITY

o Common oxidation are +4 and +2.

o Carbon also exhibits negative oxidation states.

o Compounds in +4oxidation state are generally covalent in nature.

o The tendency to show +2 oxidation state increases in the sequence Ge<Sn<Pb.

o The relative stability of +4 state decreases and +2 state increases on moving down the group due to inert pair effect

o Are electron precise molecules, do not act as Lewis acids /bases

o C cannot exceed its covalence more than 4, whereas others do so.

On account of high ionization enthalpies,

simple M4+ ions of the group are not known

Unlike carbon the other elements of the

group form compounds having coordination

numbers higher than 4 like (SiF5)-, (SiF6)2- and

(PbCl6)2-.

REACTIVITY TOWARDS OXYGEN

when heated in oxygen form two types of oxides, monoxide and dioxide of formula MO and MO2. SiO only exists at hightemperature. Among dioxides CO2, SiO2 and GeO2 are acidic,

whereas SnO2 and PbO2 are amphoteric in nature Among monoxides, CO is neutral, GeO is distinctly

acidic whereas SnO and PbO are amphoteric. Acidity of oxides increases as the oxidation state

of the element increases eg CO2 is acidic whereas CO is neutral

REACTIVITY TOWARDS WATER

C, Si and Ge are not affected by water.

Tin decomposes steam to form dioxide and dihydrogen gas.

Lead is unaffected by water, probably because of a protective oxide film formation

REACTIVITY TOWARDS HALOGEN

forms halides of formula MX2 and MX4 (where X = F, Cl, Br, I).

Except carbon, all other members react directly with halogen under suitable condition to make halides.

Most of the MX4 are covalent in nature and tetrahedral in shape

Exceptions are SnF4 and PbF4, which are ionic in nature.

Stability (thermal and chemical) of dihalides increases and those of tetrahalides decreases down the group

Eg: GeX4 is more stable than GeX2,whereas PbX2 is more than PbX4.

HYDROLYSIS OF CHLORIDES

Except CCl4,other tetrachlorides are easily hydrolysed by water because the central atom accommodate the lone pair of electrons from oxygen atom of water molecule in d orbital.

Hydrolysis SiCl4 to form Si(OH)4

IMPORTANT TRENDS ANDANOMALOUS PROPERTIES OFCARBON

Carbon differs from rest of the members due its smaller size, Higher electronegativity, higher ionisation enthalpy and unavailability of d orbitals.

Maximum co valency is 4 Carbon has unique ability to form pπ– pπ multiple

bonds with itself and with other atoms of small size and high electronegativityEg: C=C,C ≡ C, C = O, C = S, and C ≡ N.

Carbon shows catenation, tendency to show catenation decreases down the group C > > Si >Ge ≈ Sn.

Due to property of catenation and pπ– pπ bond formation, carbon is able to show allotropic forms

ALLOTROPES OF CARBON

•Carbon exhibits many allotropic forms both crystalline as well as amorphous.

•Diamond and Graphite are two well-known crystalline forms of carbon.

•Fullerenes are the most recently discovered allotrope of Carbon .

DIAMOND

It has a crystalline lattice. In diamond each carbon atom undergoes sp3

hybridisation The structure extends in space and produces a rigid

three dimensional network of carbon atoms. It is very difficult to break extended covalent bonding

and, therefore, diamond is a hardest substance on the earth.

Used as an abrasive for sharpening hard tools, in making dies and in the manufacture of tungsten filaments for electric light bulbs

STRUCTURE OF DIAMOMD

GRAPHITE Graphite has hexagonal multiple layered structure Each carbon atom in hexagonal ring undergoes sp2

hybridisation and makes three sigma bonds with three neighbouring carbon atoms. Fourth electron forms a π bond. The electrons are delocalized over the whole sheet. Electrons are mobile and, therefore, graphite conducts electricity along the sheet.

Graphite cleaves easily between the layers and, therefore, it is very soft and slippery.

used as a dry lubricant in machines running at high temperature

Graphite is thermodynamically most stable allotrope of carbon

STRUCTURE OF GRAPHITE

FULLERENES

Preparation: By heating graphite in an electric arc in the presence of inert gases such as helium or argon.

The sooty material formed by condensation of the vapours consists of C60 with smaller quantity of C70 and traces of fullerenes consisting of even number of carbon atoms up to 350 or above

C60 has a shape like soccer ball and is refered as Buckminster Fullerene fullerenesIt contains twenty six- membered rings andtwelve five membered rings. A six membered ring is fused with six or five membered ringsbut a five membered ring can only fuse with six membered rings. All the carbon atoms areequal and they undergo sp2 hybridisation. Each carbon atom forms three sigma bonds with other three carbon atoms. The remaining electron at each carbon is delocalised in molecular orbitals, which in turn give aromatic character to molecule. This ball shaped molecule has 60 vertices and each one is occupied by one carbon atom and it also contains both single and double bonds with C–C distances of 143.5 pm and 138.3 pm respectively.

Fullerenes are the only pure form of carbon because they have smoothstructure without having ‘dangling’ bonds.

Buckyball

OTHER ALLOTROPES Carbon black, coke, and charcoal are all impure forms

of graphite or fullerenes. Carbon black is obtained by burning hydrocarbons in a

limited supply of air. Charcoal and coke are obtained by heating wood or

coal respectively at high temperatures in the absence of air.

USES OF CARBON

Graphite fibres are used in products such astennis rackets, fishing rods, aircrafts and canoes.

Graphite is used for electrodes in batteries and industrial electrolysis. Crucibles made from graphite are inert to dilute acids and alkalies.

activated charcoal is used in adsorbing poisonous gases; also used in water filters to remove organic contaminators and in air conditioning system to control odour.

Carbon black is used as black pigment in black ink and as filler in automobile tyres.

Coke is used as a fuel and largely as a reducing agent in metallurgy.

Diamond is a precious stone and used in jewellery. It is measured in carats (1 carat = 200 mg).

SOME IMPORTANT COMPOUNDS OF

CARBON AND SILICON

OXIDES OF CARBON

OXIDES OF CARBONPreparation:•Direct oxidation of C in limited supply of oxygen

•Dehydration of formic acid with concentrated H2SO4 (small scale)

•by the passage of steam over hot coke.

•When air is used instead of steam, a mixtureof CO and N2 is produced, which is calledproducer gas2C(s) +O2 (g)+ 4N 2(g)1273K 2CO(g)+4N 2(g)

Water gas and producer gas are very important industrial fuels.

Carbon monoxide in water gas or producer gas can undergo further combustion forming carbon dioxide with the liberation of heat.

Carbon monoxide is a colourless, odourless and almost water insoluble gas.

It is a powerful reducing agent and reduces almost all metal oxides other than those of the alkali and alkaline earth metals, aluminium and a few transition metals.

?CATENATION IN CARBON

Carbon atoms have the tendency to link with one another through covalent bonds to form chains

and rings. Reason :Bond Dissociation enthalpy

C—C bonds are very strong. Down the group the size increases and electronegativity decreases, and, there by tendency to show catenation decreases.