P B LOC KG R O U P 14E L E M E N TS SANTOSH SAKSHAM SARANSH SAYUJ SUVARCHA XI B
T H E E L E M E N T S INT H E G R O U P 14 A R E :
IN T R O D U CT IO N¤ In modern IUPAC notation, it is called Group 14.¤ In the old IUPAC and CAS systems, it was called Group IVB and Group IVA, respectively.¤ The family is particularly interesting because it consists of one non- metal (carbon), two metals (tin and lead), and two metalloids (silicon and germanium).¤ The atoms of all Group 14 elements have four electrons in their outermost energy level. In spite of this fact, the elements have less in common physically and chemically.
G e ne ra lin f o r m a t io n APPEARANCECarbon is a dull black colour in the form of graphite, or hard andtransparent in the form of diamond; silicon and germanium are dullgrey or black; tin and lead are a shiny grey colour. GENERAL REACTIVITYIn Group 14 the elements change from non-metallic in character at thetop of the Group to metallic at the bottom. Silicon is chemicallyunreactive. Germanium is also unreactive . Both tin and lead aregenerally unreactive metals. OCCURRENCE AND EXTRACTION Carbon, tin and lead can all be found in the elemental form in the Earth’s crust, and are readily mined. Silicon is found in mineral deposits and purified from them.
PHYSICALPROPERTIESThe physical properties of Group 14 elements vary quite widely from one element toanother, consistent with the increasing metallic character on descending the Group.The structures change from giant molecular lattices in carbon and silicon to giantmetallic lattices in tin and lead, and this is the reason for the changes in physicalproperties.The change in bonding from covalent to metallic down the Group causes a decrease inmelting point, boiling point, heat of atomisation and first ionisation energy.At the same time, the increasing metallic character causes a general increase in densityand conductivity.Diamond has a very high refractive index (the reason for its sparkle) and this, alongwith its rarity, has made it valuable as a jewel. However, it is also the hardest naturalsubstance known and so is important industrially.The most important physical property of silicon is that it is a semi-conductor. Smallsilicon chips, just a few millimetres square, have revolutionised the computer andmicroprocessor industries.Tin and lead, as typical metals, are good conductors of electricity.
HEMICAL PROPERTIES In general, chemical reactivity increases on descending the Group. Carbon has the unique ability to form stable compounds containing long chains and rings of carbon atoms, called catenation, which results in carbon forming an enormous range of organic compounds. The C-C and C-Si bond energies are very similar, so many organo-silicon compounds are known. Silicon does not, however, form multiple bonds. Silicon is unreactive chemically because an oxide layer seals the surface from attack, and high temperatures are required for oxidation to occur. However, Silicon does react with fluorine at room temperature. It is not attacked by aqueous acids, but does react with concentrated alkalis. Tin and lead are quite easily oxidised, tin usually to tin (IV) and lead to lead (II). Both tin and lead reduce the halogens.
TY OXIDECO (gas), CO2 (gas), SiO2 (solid), SnO2 (solid),SPbO (solid), Pb3O4 (solid), PbO2 (solid).Oxides with a lower oxidation number become more stable going down the Group.Silicon forms a strong bond with oxygen in silica, SiO2. Oxo-anions derived fromsilica are called silicates. They are very common in nature and have structures basedon SiO4 tetrahedral shape. One material containing these is asbestos.CO2 is acidic, as is CO under extreme conditions. SiO2 is acidic; it reacts with hotconcentrated alkali. SnO, SnO2, PbO and PbO2 are all amphoteric. HALIDE SAll the elements of Group 14 form tetrahalides, but only tin and lead form dihalides.The tetrahalides are covalent tetrahedral molecules whereas the dihalides are bestregarded as ionic. HYDRIDE S The hydrides of carbon are the hydrocarbons - organic compounds. Silicon forms a series of hydrides called the silanes, with the general formula SinH2n+2.
Oxidation States andIonisation EnergiesGroup IV elements exist in two oxidation states, +2 and +4. Thereis a steady increase in the stability of the +2 oxidation state ondescending the Group.The elements in this Group have four electrons in their outermostshell, two s electrons and two p electrons.The first four ionisation energies rise in a fairly even manner,and the fifth ionisation energy is very large, reflecting theremoval of an electron from a filled level nearer to the nucleus.Compounds of tin and lead in which the Group 14 element has anoxidation number +2 are regarded as ionic. In these compounds,the Sn+2 and Pb+2 ions are formed by loss of the outermost twoelectrons, whilst the two s electrons remain relatively stable intheir filled sub-shell. This is called the “Inert Pair Effect".
INDUSTRIALINFORMATIONThe industrial importance of carbon in petrochemicals is immense.These hydrocarbons are used extensively in almost all areas ofmodern civilisation; clothing, dyes, fertilisers, agrochemicals, fuelsand new materials.Silicon also contributes to new technology in the silicon chip, whichhas revolutionised the computer and high-tech industries.Germanium is, like silicon, a semi-conductor used in similar devices,but it is less widely used.Tin is used as a coating for other metals to prevent corrosion, such asin tin cans, but it is in alloys that tin is used most extensively. Theseinclude bronze, soft solder, type metal, phosphor bronze and pewter.Lead is used in great quantities in storage batteries,cable covering,for roofing in buildings and for radiation shielding. It was used inthe manufacture of tetraethyl lead, an anti-knocking compoundadded to petrol, but this was shown to be an environmental hazard.
ELEMENT ATOMIC RELATIVE MELTING DENSITY NUMBER ATOMIC POINT (K) (kg/m 3 ) CARBON 6 MASS 12.011 3830 3513 SILICON 14 28.086 1683 2329GERMANIU 32 72.61 1210.6 5323 M TIN 50 118.71 505.1 7130 LEAD 82 207.2 600.65 11350
A characteristic property of the elements ofgroups 14 is that these show allotropy.Allotropy is the existence of an element intwo or more forms, which are significantlydifferent in physical properties but havesimilar chemical properties.The difference may be due to difference incrystal structure, the number of atoms in themolecule of a gas or the molecular structureof a liquid.
c a rbonCarbon is the chemical element with symbol C and atomicnumber 6. As a member of group 14 on the periodic table, it isnon-metallic and tetravalent—making four electronsavailable to form covalent chemical bonds.Carbon is found free in nature in four allotropic forms;fullerene, graphite and diamond and amorphous.Carbon is also found in combination inhydrocarbons (methane gas, oil and coal), andcarbonates (limestone and dolomite).The concept of oxidation states is rarely used indiscussing carbon in its compounds because ofsubtleties of bonding. However, in singlecompounds it can be regarded as havingoxidation states of C-4, C+2, C+4.
c a rbonCarbon is found free in nature in four allotropic forms:Amorphous, Graphite, Diamond and Fullerenes.Graphite is used in lubricants and diamond is one of thehardest known materials.Carbon is the basis of all life as part of the DNA molecule.The difference is purely because of the arrangement of atoms ineach of the two forms.
c a rbonIn diamond, the atoms are arranged tetrahedrally in a vastcontinuous array.In graphite, hexagonal rings are joinedtogether to form sheets, and the sheets lie one on top of the other.In 1961 the International Union of Pure and Applied Chemistry[IUPAC] adopted the isotope carbon-12 as the basis for relativeatomic masses. Carbon atoms in diamond Carbon atoms in graphite
USES Carbon-14, with a half-life of 5770 years, is used to date materials such as wood, archeological specimens etc. Diamond is used in jewelry and surgical instruments. Graphite is used as a lubricant. It is the building block of fossil fuels (gasoline and oil) and Basis of organic chemistry. It is also an indispensable source of such varied everyday products as Nylon and petrol, perfume and plastics, shoe polish, DDT and TNT.
CARBON DATINGCarbon dating is a variety of radioactive dating which is applicable only to matter which was once living and presumed to be in equilibrium with the atmosphere, taking in carbon dioxide from the air for photosynthesis.Cosmic ray protons blast nuclei in the upper atmosphere, producing neutrons which in turn bombard nitrogen, the major constituent of the atmosphere . This neutron bombardment produces the radioactive isotope carbon-14. The radioactive carbon-14 combines with oxygen to form carbon dioxide and is incorporated into the cycle of living things.The carbon-14 forms at a rate which appears to be constant, so that by measuring the radioactive emissions from once-living matter and comparing its activity with the equilibrium level of living things, a measurement of the time elapsed can be made.
In upper atmosphere7 N14 + 0n1 6 C14 + 1H1 C14 + O2 C14O2C14O2 + H2O GLUCOSE At the time of destruction6 C14 7 N14 + -1β0
AGECALCULATION N λ = 2.303 log 0 t N Since λ = 0.6931 t1/2 Therefore; 0.6931 = 2.303 log N0 t1/2 t NWhere λ = Disintegration constant t = Age of the material N0 = Initial β ray emission N = Final β ray emission t1/2 = half life of the material i.e. generally 5770 years
S ilic o nSilicon is the most common metalloid.It has the symbol Siand atomic number 14. A tetravalent metalloid, silicon isless reactive than its chemical analog carbon.Crystalline silicon has a metallic luster and grayish color.Silicon is a relatively inert element, but it is attacked byhalogens and dilute alkali. Most acids, except hydrofluoric, do notaffect it.Silicon is essential to plant and animal life. It is non-toxic but somesilicates, such as asbestos, are carcinogenic.
GENERALINFORMATION Silicon is relatively inert. It is attacked by halogens and dilute alkali, but is not attacked by acids except hydrofluoric. Silicones are important products of silicon, prepared by hydrolyzing a silicon organic chloride. Hydrolysis and condensation of substituted chlorosilcanes can be used to produce a great number of polymers known as silicones, ranging from liquids to hard, glasslike solids, with many useful properties. OXIDATION STATES Si+2, Si+4
S ilic o n Amorphous silicon is a brown powder, and crystalline silicon is a grey colour with a metallic lustre. Silicon makes up 25.7% of the Earths crust by mass and is the second most abundant element (oxygen is the first). It does not occur free in nature but occurs chiefly as the oxide and as silicates. The oxide includes sand, quartz, rock crystal, amethyst, agate, flint and opal. The silicate form includes asbestos, granite hornblende, feldspar, clay and mica. Silicon is prepared commercially by electrolysis with carbon electrodes of a mixture of silica and carbon. Silicon is used extensively in solid-state devices, and for this hyper pure silicon is required before tiny controlled amounts of specific impurities are added. This is prepared by thermal decomposition of ultra-pure trichlorosilane. Some workers such as miners and stonecutters who are exposed to siliceous dust often develop a serious lung disease called silicosis.
USESSilicon is one of the most useful elements tomankind. Sand and clay, which both containsilicon, are used to make concrete andcement.It is the principal ingredient of glass, whichhas thousands of uses.It is a component of steel, and silicon carbidesare important abrasives and also used inlasers.It is present in pottery and enamels, and inhigh-temperature materials.silicon is increasingly used in micro-electronic devices.
g e rma niu mGermanium is a chemical elementwith the symbol Ge and atomicnumber 32. It is a lustrous, hard,grayish-white metalloid in thecarbon group, chemically similarto its group neighbors tin andsilicon. Germanium has fivenaturally occurring isotopesranging in atomic mass numberfrom 70 to 76. It forms a largenumber of organic metalliccompounds, includingtetraethylgermane andisobutylgermane.
g e rma nium Germanium is a grey-white metalloid, crystalline and brittle, retaining a lustre in air. Germanium is found in small quantities in the minerals germanite and argyrodite. It is also present in zinc ores, and commercial production of germanium is by processing zinc smelter flue dust. It can also be recovered from the by-products of combustion of certain coals. OXIDATION STATES Ge+2, Ge+4
USESGermanium is a very important semiconductor. The pure element isdoped with arsenic, gallium or other elements and used as atransistor in thousands of electronic applications.Germanium is used as an alloying agent, in fluorescent lamps and asa catalyst. Both germanium and germanium oxide are transparentto infrared radiation and so are used in infrared spectroscopes.Germanium oxide has a high index of refraction and dispersion andis used in wide-angle camera lenses and microscope objectives.Germanium has no known biological role. It is non-toxic. Certaingermanium compounds have low mammalian toxicity but markedactivity against some bacteria, which has stimulated interest intheir use in pharmaceutical products.
t inTin is a chemical element with the symbol Sn and atomic number 50.It is a silvery-white metal.It is soft, pliable and has a highly crystalline structure.Tin shows chemical similarity to both neighboring group 14 elements,germanium and lead and has two possible oxidation states, +2 and +4,with the +4 state being slightly more stable than the 2+ state.Tin is the 49th most abundant element and has, with 10 stable isotopes,the largest number of stable isotopes in the periodic table.Tin is obtained chiefly from the mineral cassiterite, where it occurs astin dioxide, SnO2. It is obtained commercially by reducing the ore withcoal in a reverberatory furnace.
t inTin is non-toxic. Trialkyl and Triaryl tincompounds are used as biocides and must behandled with care.Tin is unreactive to water and oxygen, as it isprotected by an oxide film. It reacts with acidsand bases. When heated in air, tin forms tin(IV)oxide which is feebly acidic.When a tin bar is broken, a "tin cry" is hearddue to the breaking of the tin crystals.Tin has two allotropic forms. On warming, greytin, with a cubic structure, changes into whitetin, the ordinary form of the metal.
USESIt takes a high polish and is used to coat other metals toprevent corrosion, such as in tin cans which are made oftin-coated steel.Alloys of tin are important, such as soft solder, pewter,bronze and phosphor bronze.The most important tin salt used is tin(II) chloride whichis used as a reducing agent and as a mordant.Tin salts sprayed onto glass are used to produceelectrically conductive coatings.Most window glass is made by floating molten glass onmolten tin to produce a flat surface.Recently, a tin-niobium alloy that is superconductive atvery low temperatures has attracted interest.
le a dLead is a main-group element with symbol Pb andatomic number 82.Lead is a soft, malleable poor metal. It is also countedas one of the heavy metals.Metallic lead has a bluish-white color after beingfreshly cut, but it soon tarnishes to a dull grayishcolor when exposed to air.Lead has a shiny chrome-silver luster when it ismelted into a liquid.Lead is a soft, weak, ductile metal with a pale greysheen.
le a dLead is obtained chiefly from the mineral galena by a roasting process.It is a poor conductor of electricity.It is a poisonous substance to animals.It damages the nervous system and causes brain disorders.Excessive lead also causes blood disorders in mammals. OXIDATION STATES Pb+2, Pb+4
le a dLead has no known biological role.It is toxic in a cumulative way:Teratogenic (an agent that can disturb the development of the embryo orfetus) .Carcinogenic (any substance, radionuclide or radiation, that is an agentdirectly involved in causing cancer).Lead is stable to air and water, but will tarnish in moist air over longperiods. It dissolves in nitric acid. Lead is a poor conductor of electricity.
USESLead is very resistant to corrosion, and is often used to store corrosiveliquids.Great quantities of lead, both as the metal and the dioxide, are used inbatteries.Lead is also used in cable covering, plumbing and ammunition.Tetraethyl lead is used as an anti-knock agent in petrol, and as an additivein paints.The use of lead in plumbing, petrol and paints has been reduced in the pastfew years because of environmental concern, as lead is a cumulative poisonand is thought to affect brain development and function, especially in youngchildren.Lead is an effective shield around X-ray equipment and nuclear reactors.Lead oxide is used in the production of fine crystal glass.
UNUNQUADIUMELEMENT 114, representing the beachhead ofwhat might be an "island of stability" amongheavy nuclei, has been successfully created,according to scientists at Russias Joint Institutefor Nuclear Research (JINR).Artificially made elements heavier thanuranium are generally unstable, but theoristshave for some time thought that for elements inthe vicinity of number 114 and above might wellpossess a configuration of neutrons and protonsthat makes for longer life.The lifetimes for elements 114 and 112 are 30seconds and 280 ms, respectively. Element 113has not yet been discovered.