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

263 Pages·2021·7.402 MB·English

by  Awadhesh Kumar Singh A K Singh

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