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Foundation Science Chemistry for Class 10 Awadhesh Kumar Singh A K Singh Bharati Bhawan PDF

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Preview Foundation Science Chemistry for Class 10 Awadhesh Kumar Singh A K Singh Bharati Bhawan

F o u n d a t i o n S c i e n c e C H E M I S T R Y FOR CLASS 10 Awadhesh Kumar Singh, PhD PREFACE The latest edition of Foundation Science: Chemistry for Class 10 has been thoroughly revised according to the new syllabus of NCERT. The text has been written in a simple and easy-to-understand style. A lot of information has been presented in tabular and point-wise formats that should aid quick learning, comparison of facts, etc. The diagrams are fairly large, and they have been drawn and labelled as clearly and as simply as possible. Class 10 is possibly the most important stage in a student’s academic career, for at the end of this class the student takes the first public examination. Success in this examinationdependsonthestudent’sabilitytoanswerquestionscorrectly.Andthatis possible only when the student gets adequate practice with all the types of questions that are framed in the board examination. The Exercises section has been structured to addressthisneed.Besides,objectivequestions,whichtestastudent’sunderstandingso well, have also been given. I take this opportunity to express my cordial thanks to the management and productionteamofBharatiBhawanfortheirall-outeffortstopublishthebookinavery short time. Finally, I must thank my son Sanjeev Kumar, without whose assistance the preparation of the manuscript would have been an uphill task. I would like to get feedback from all those who use this book so that any shortcoming can be rectified immediately. Author (iii) CONTENTS 1. Periodic Classification of Elements 1 2. Elementary Idea of Bonding 22 3. Chemical Reactions 33 4. Acids, Bases and Salts 53 5. Metals and Nonmetals 73 6. Compounds of Common Use 120 7. Carbon Compounds 133 8. Conservation and Management of 170 Natural Resources 9. Practicals 190 Question Bank 232 Additional Questions 257 (cid:2) (v) 1 Periodic Classification of Elements INTRODUCTION PeriodicClassificationofElements Scientists havediscovered111 chemical elementstill date. Someof theseelementsoccurin free stateandsomeincombinedstate.Butalloftheseelementswerenotdiscoveredinaday. Whena veryfewelementswereknown,studyingthemseparatelywasnotaproblem.Butwhenalarge numberofelementshadbeendiscovered,itbecamedifficulttostudythepropertiesofallofthem separately.So,attemptsweremade,fromtimetotime,tosortouttheelementsintogroupssoas tofollowtheirbehaviourinanorderlymanner.Thestudyofthepropertiesofatypicalelementof a particular group enables scientists to predict roughly the properties of other elements of that group.Wewillnowbrieflydiscussthevariousattemptsmadetoclassifyelements. EARLY ATTEMPTS AT CLASSIFICATION Lavoisier’s Classification Lavoisier classified elements into metals and nonmetals. This classification was based on certain distinctive physical properties such as hardness, malleability and lustre. On the basis of these properties,sodiumandleadwereclassedtogetherasbelongingtothegroupofmetals. Limitations (i)Hardness,malleabilityandlustrewerefoundtobetheonlycommonpropertiesof sodiumandlead,otherwisethetwoelementswereentirelydifferent. (ii) In such a classification there was no place for elements with properties resembling those of metalsaswellasnonmetals. Therefore,Lavoisier’sclassificationwasfoundtobeinadequate. Dobereiner’s Classification Lawoftriads In 1817, German chemist Johann Dobereiner classified elements having similar chemical properties into groups of three. These groups were called triads. He proposed a law knownas Dobereiner’slaw oftriads. Accordingtothislaw, whenelementsarearranged inthe orderofincreasingatomicmassinatriad,theatomicmassofthemiddleelementwasfoundtobe approximatelyequaltothearithmeticmeanoftheatomicmassesoftheothertwoelements. SetI SetII SetIII Element Atomic Element Atomic Element Atomic mass mass mass Calcium 40 Lithium 7 Chlorine 35.5 Strontium 87.5 Sodium 23 Bromine 80 Barium 137 Potassium 39 Iodine 127 Averageoftheatomicmassesof Averageoftheatomicmassesof Averageoftheatomicmassesof calciumandbarium lithiumandpotassium chlorineandiodine 40(cid:3)137 7(cid:3)39 35.5(cid:3)127 (cid:2) (cid:2)88.5 (cid:2) (cid:2)23 (cid:2) (cid:2)81.2 2 2 2 Atomicmassofstrontium (cid:2)87.5 Atomicmassofsodium(cid:2)23 Atomicmassofbromine(cid:2)80 1 2 FoundationScience:ChemistryforClass10 The classification of elements into triads was very successful in predicting the atomic mass and properties of the middle element. Further, this classification showed that there exists some relationshipbetweenthepropertiesofelementsandtheiratomicmasses.Thispavedthewayfor futureattemptsatclassificationofelements. Limitation Alltheelementscouldnotbegroupedintotriads. Newlands’ Classification Lawofoctaves In 1864, John Newlands, an English chemist, showed that when elements are arrangedintheorderoftheirincreasingatomicmasses,theeighthelement,startingfromagiven element,wasakindofrepetitionofthefirstone,liketheeighthnoteinanoctaveofmusic,i.e., sa re ga ma pa dha ni sa, wherethefirstandtheeighthnotearethesame. ApartofNewlands’classificationisgivenbelowwherethefiguresunderthesymbolsshow theatomicmasses. OctavesofmusicandNewlands’arrangementofelements Indian: sa re ga ma pa dha ni Octaves sa Western: do re mi fa so la ti do Newlands’arrangement H Li Be B C N O ofelementswithatomic 1.0 7.0 9.0 11.0 12.0 14.0 16.0 masses F Na Mg Al Si P S 19.0 23.0 24.0 27.0 28.0 31.0 32.0 Cl K Ca Cr Ti Mn Fe 35.5 39.0 40.0 52.0 48.0 55.0 56.0 CoandNi Cu Zn Y In As Se 58.93and58.71 63.54 65.37 88.90 114.82 74.92 78.96 Br Rb Sr CeandLa Zr — — 79.90 85.47 87.62 140.12and 91.22 138.91 Starting from lithium (Li) the eighth element is sodium (Na). The eighth element starting from sodium is potassium. The properties of lithium, sodium and potassium are similar. The propertiesofberyllium,magnesiumandcalciumaresimilartoo. Limitations (i) This law worked well for lighter elements (up to calcium), but it could not be applied to heavier ones (elements of higher atomic masses) because starting from calcium everyeighthelementwasfoundtohavepropertiesdifferentfromthoseofthefirstelement. (ii) Newlandsemphaticallysaidthatonly56elementsdoexistinnatureandnomoreelementis likely to be discovered in future. But this conceptwas later on found to be untrue with the discoveryofmanynewelementswhichdefiedthelawofoctaves. (iii) Inarrangingelementsintheformofatable,Newlandsclubbedtwoelementstogetheratthe sameplaceandinthesamecolumn.Notonlythis,healsoplacedsomedissimilarelementsin the same column. For example, cobalt (Co) and nickel (Ni) were clubbed together in the columnoffluorine(F),chlorine(Cl)andbromine(Br)(undersa/do).Weknowthatcobaltand nickel have properties entirely different from those of fluorine, chlorine and bromine. It is PeriodicClassificationofElements 3 alsoknownthatcobaltandnickelhavepropertiessimilartothoseofiron.Butiron(Fe)was placedinacolumn(underni/ti)differentfromthecolumnofcobaltandnickel. However,thislawlentsupporttotheideathatthepropertiesofelementsdependuponthe atomicmasses.Italsoshowedthatthepropertiesofelementsarerepeatedafteracertaininterval, i.e.,thepropertiesofelementsareperiodicinnature. MENDELEEV’S PERIODIC LAW AND PERIODIC TABLE While working systematically on the physical and chemical properties of elements, Dmitri IvanovichMendeleevnoticedthatpropertiesofelementsvariedregularlywiththeatomicmass. Hearrangedthe63elementsthenknowninatableonthebasisofsimilaritiesinproperties.Itwas found thatmostof theelementsoccupiedplaces in thetable in orderof theirincreasing atomic masses.In1869,Mendeleevformulatedalaw,nowknownastheperiodiclaw.Thelawisstated asfollows. Thepropertiesofelementsare periodicfunctionsoftheiratomicmasses. Thismeans, if the elementsarearrangedinorderofincreasingatomicmassesthenthosewithsimilarpropertiesare repeatedatregularintervals. Onthebasisoftheperiodiclaw,Mendeleevpresentedhisclassificationintheformofatable, now known as Mendeleev’s periodic table. A simplified version of this periodic table is given (Table1.1).Inthistable,copper,silverandgoldfindplacesingroupsIaswellasVIII. Dmitri Ivanovich Mendeleev Dmitri Ivanovich Mendeleev was born in Tobolsk(Siberia),on8February1834.After his early education, he joined university only due to the efforts of his aged mother. HereceivedaMaster’sdegreeinchemistry in 1856, and a doctoral degree in 1865. He was appointed Professor of General Chemistry in 1867 at the University of St. Petersburg. In 1869, he proposed the famous Periodic Law and constructed the Periodic Table of elements.Inthis table, he placedcertainelementsinspecificpositions inaccordancewiththeirproperties.Healso predicted the properties of some undiscoveredelements. Mendeleevwasaversatilegenius.Hewasinterestedinmanyareasofscience.Heworked alotonnaturalresourcestoo.In1890,heresignedhisprofessorship,andwasappointedthe Director of the Bureau of Weights and Measures. Mendeleev dedicated all his works to his mother. To name the element with atomic number 101 mendelevium was proposed to honour MendeleevbyAmericanscientistGlennT Seaborg,thediscovereroftheelement. MendeleevdiedinFebruary1907. 4 FoundationScience:ChemistryforClass10 Table1.1 Mendeleev’speriodictable:63elementswereknownthen.(Thenumbersindicate theatomicmassesofelements.) Groups(cid:4) I II III IV V VI VII VIII Periods(cid:5) 1 H 1 2 Li Be B C N O F 7 9.4 11 12 14 16 19 3 Na Mg Al Si P S Cl 23 24 27.3 28 31 32 35.5 4 K Ca ? Ti V Cr Mn Fe Co Ni Cu 39 40 44 48 51 52 55 56 59 59 63 5 Cu Zn ? ? As Se Br 63 65 68 72 75 78 80 6 Rb Sr Yt Zr Nb Mo ? Ru Rh Pd Ag 85 87 88 90 94 96 100 104 104 106 108 7 Ag Cd In Sn Sb Te I 108 112 113 118 122 125 127 8 Cs Ba Di Ce ? ? ? ? 133 137 138 140 9 ? ? ? ? ? ? ? 10 ? ? Er La Ta W ? OS Ir Pt Au 178 180 182 184 195 197 198 199 11 Au Hg Tl Pb Bi ? ? 199 200 204 207 208 12 ? ? ? Th ? U 231 240 This table consists of vertical columns called groups and horizontal rows called periods. Thereareonlyeightgroupsinthetable.Mendeleevleftsomevacantplaces(shownbyquestion marks)fortheyetundiscoveredelements.Noblegaseswerenotdiscoveredthen.So,hedidnot provideanyplacefortheminhisperiodictable. Mendeleev’s idea was remarkable in that he used a fundamental atomic property (atomic mass) as the basis of classification. While classifying elements he laid special emphasis on twofactors. 1. Similarelementsweregroupedtogether. 2. Elementswerearrangedinorderofincreasingatomicmasses. Modified Version of Mendeleev’s Periodic Table The elements which were undiscovered and for whom Mendeleev had left vacant places were discovered later. Some of these are scandium (Sc), gallium (Ga) and germanium (Ge). These elementswereaccommodatedintheirproperplacesinthetable.Theelementshelium(He),neon (Ne),argon(Ar),krypton(Kr),xenon(Xe)andradon(Rn)becameknownonlytowardstheendof thenineteenthcentury.Theseelements,callednoblegases,wereplacedinthetableasaseparate group,called0(zero)group.Theperiodictablehadtobemodifiedthen.Themodifiedversionof thetableisshown(Table1.2). PeriodicClassificationofElements 5 Table1.2 ModifiedversionofMendeleev’speriodictable Groups(cid:4) I II III IV V VI VII VIII 0 Periods(cid:5) A B A B A B A B A B A B A B 1 H He 2 Li Be B C N O F Ne 3 Na Mg Al Si P S Cl Ar 4 K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr 5 Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe 6 Cs Ba La* Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn 7 Fr Ra Ac** Lanthanideseries* Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu (alongwithlanthanum) Actinideseries** Th Pa U Np Pu Am Cm Bk Cf Es Fm Md No Lr (alongwithactinium) FeaturesofthemodifiedversionofMendeleev’speriodictable 1.Groupsintosubgroups Each group of this periodic table is further divided into two subgroupsAandB.Thepropertiesofelementswithinasubgroupresemblemoremarkedlybut theydifferfromthoseoftheelementsoftheothersubgroups.Forexample,lithium(Li),sodium (Na), potassium (K), etc., of subgroup IA have close resemblance of properties but they have hardlyanyresemblancetothecoinagemetals(Cu,AgandAu)ofsubgroupIB. Mendeleevallowedthesubgroupstoberepresentedwithinthesamegroup. 2.Predictionoferrors This periodic table could predict errors in the atomic masses of some elementsonthebasisoftheirpositionintheperiodictable.Forexample,whentheperiodictable waspublished,theexperimentalvalueoftheatomicmassofberyllium(Be)wassupposedtobe 13.65anditsvalency,3.So,thepositionofBeshouldhavebeensomewhereelse,butMendeleev placed it at its appropriate position on the basis of its properties. He further suggested that the atomicmassofBeneededcorrection.Mendeleevpredicteditsatomicmasstobe9.1andvalency, 2.Laterinvestigationsprovedhimright. Similarly,theatomicmassofuraniumwascorrectedfrom120to240.Correctionswerealso madeintheatomicmassesofgold,platinum,etc. 3.Predictionsofpropertiesofhithertoundiscoveredelements We know that Mendeleev classifiedtheelementsinorderoftheirincreasingatomicmasses.However,thisorderhadtobe ignoredatsomeplacestomakesurethattheelementswithsimilarpropertiesfellinthesamegroup. In doing so, he left some vacant places in the table. These vacant places were kept reserved for elementsnotdiscoveredtillthen.Mendeleevwasconfidentthattheseelementswouldbediscovered laterandtheywouldoccupythesevacantplaces.Notonlythis,healsopredictedthepropertiesof theseundiscoveredelementsonthebasisofhisstudyofthepropertiesoftheneighbouringelements. Amazingly,whenthemissingelementsofMendeleev’speriodictablewerediscoveredsubsequently, theirpropertieswerefoundtobeverysimilartothosepredictedbyMendeleev. Theelementsscandium,galliumandgermaniumwerenotknownin1871buttheirexistence was predicted by Mendeleev. He named these elements as eka-boron, eka-aluminium and eka-silicon. When these elements were discovered, they were named scandium, gallium and germanium respectively and their properties were found to be in good agreement with those 6 FoundationScience:ChemistryforClass10 predictedbyMendeleev.Propertiesofeka-aluminium(predictedbyMendeleev)andthoseofthe gallium(discoveredlater)aregiveninTable1.3. Table1.3 Property Eka-aluminium Gallium Atomicmass 68 69.7 Formulaofoxide E O Ga O 2 3 2 3 Formulaofchloride ECl GaCl 3 3 Consideringitsatomicmass,titanium(Ti)shouldhavebeenplacedbelowaluminiuminthe periodictable,butMendeleevplaceditbelowsilicon(Si)becausethepropertiesoftitaniumwere similartothoseofsilicon.Thus,agapwasleftbelowaluminiumintheperiodictable.Thisgap wasfilledupbygalliumwhichwasdiscoveredlater.Thepropertiesofgallium(Ga)werefound tobesimilartothoseofboronandaluminium. 4.Basicfeaturesintact AllthebasicfeaturesofMendeleev’speriodictableareintacteventoday. Even when a new class of elements, i.e., noble gases, were discovered, they found place in a separate group called the zero group. The existing order of the periodic table was not at alldisturbed. DiscrepanciesinMendeleev’speriodictable Mendeleev’speriodictablehasthefollowingdefects. 1.Positionofhydrogen Thepositionofhydrogenintheperiodictableisanomalous.Hydrogen resemblesalkalimetals(Li,Na,K,etc.)incertainproperties.Hence,itisplacedingroupIAalong withthealkali metals.Butcertainpropertiesofhydrogenresemblethoseofhalogens(F,Cl,Br, etc.).Soitmaybeplacedinthegroupofthehalogens(VIIA). 2.Positionoflanthanidesandactinides The elements from atomic number 57 to 71 are collectivelyknownaslanthanides.Theydonothaveaproperplaceintheperiodictable.Theyall havebeenplacedatthesamepositioningroupIIIandperiod6.Similarly,theactinides(atomic numbers89–103)alsohavenoproperplaceintheperiodictable.Theseelementshavealsobeen placedinthesameposition,ingroupIIIandperiod7. 3.Some similar elements are separated, while some dissimilar elements have been placed in the samegroup Somesimilarelementsareseparatedintheperiodictable.Forexample,copper(Cu) and mercury (Hg), silver (Ag) and thallium (Tl), and barium (Ba) and lead (Pb). On the other hand, some dissimilar elements have been placed together in the same group. For example, copper(Cu),silver(Ag)andgold(Au)havebeenplacedingroupIalongwiththealkalimetals. Similarly,manganese(Mn)isplacedinthegroupofthehalogens. 4.Presenceofsomeanomalouspairsofelements In Mendeleev’s periodic table, the elements arearrangedinorderofincreasingatomicmass.Insomeplaces,thisorderhasbeenignored. (a) The atomic mass of argon is 40 and that of potassium is 39. But argon is placed before potassiumintheperiodictable. (b) Thepositionsofcobaltandnickelarenotinproperorder.Cobalt(at.mass(cid:2)58.9)isplaced beforenickel(at.mass(cid:2)58.6). (c) Tellurium(at.mass(cid:2)127.6)isplacedbeforeiodine(at.mass(cid:2)126.9). (d) Thorium(at.mass(cid:2)232.12)isplacedbeforeprotactinium(at.mass(cid:2)231). PeriodicClassificationofElements 7 Anomalouspairsofelements Element(cid:4) Ar K Co Ni Te I Th Pa Atomicmass 40 39 59.9 58.6 127.6 126.9 232.12 231 Group 0 IA VIII VIII VIB VIIB IIIB IIIB 5.Positionofisotopes Theisotopesofanelementhavenoplaceintheperiodictable. ThefailureofMendeleev’speriodiclawtoexplainthewrongorderoftheatomicmassesof some elements and the position of isotopes led scientists working in this field to conclude that atomic mass cannot be the basis for the classification of elements. There must be a more fundamentalpropertyofelementswhichcanbethebasisofclassification. MODERN PERIODIC TABLE Mendeleev’s periodic table was based on atomic mass. Though most of the elements could be arranged in the periodic table in the order of increasing atomic masses, there were some exceptions. For example, iodine (I) and tellurium (Te). In 1913, Moseley from his studies on X-rays found that the atomic number (i.e., proton number) is the fundamental property of an elementandnotitsatomicmass.Thus,atomicnumberwasadoptedasthebasis ofthemodern periodictable.Theperiodiclawwasthenformulatedas: The physical and chemical properties of elements are a periodic function of their atomicnumbers. Inotherwords,iftheelementsarearrangedintheorderoftheirincreasingatomicnumbers, theelementswithsimilarpropertiesarerepeatedatregularintervals. Basedonmodernperiodiclaw,variousotherformsoftheperiodictablewereproposed,but the main structure of the table as proposed by Mendeleev was never disturbed. However, the formofthetablewhichiscommonlyusedatpresentisknownasLongorExtendedFormofthe periodictable.Itisbasedupontheelectronicconfigurationofelements. Initially,thenumberingofgroupswasdoneinRomannumeralsasIA,IIA,IIIB,IVB,VB, VIB,VIIB,VIII,IB,IIB,IIIA,IVA,VA,VIA,VIIAand0.GroupVIIIconsistedofthreegroups. Thusthetotalnumberofgroupsbecame18.AccordingtothelatestrecommendationoftheIUPAC (International Union of Pure and Applied Chemistry) the notations such as A and B have been removedandthenumberingofgroupshasbeendoneinArabicnumeralsas1,2,3,4,5upto18 (Table1.4). Description 1. Inthisperiodictabletheelementsarearrangedinorderofincreasingatomicnumber. 2. Therearesevenperiods.Theelementsintheperiodsareasfollows: 1stperiodcontains2elements,H(1)andHe(2) 2ndperiodcontains8elements,Li(3)toNe(10) 3rdperiodcontains8elements,Na(11)toAr(18) 4thperiodcontains18elements,K(19)toKr(36) 5thperiodcontains18elements,Rb(37)toXe(54) 6thperiodcontains32elements,Cs(55)toRn(86) 7thperiodcontains25elements,startingfromFr(87).Thisperiodisstillincomplete. Thesecondandthethirdperiods,containing8elementseach,arecalled shortperiods.The fourthandthesucceedingperiodsarethelongperiods. 3. Thetablehas18verticalcolumns(excludinglanthanidesandactinides),andthecolumnsare numberedas1,2,3,…,18. 4. Inthistable,thesubgroupsofMendeleev’speriodictablearekeptseparated.Theelements belonging to groups 1, 2, 13–17 are called normal or representative elements and those

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