Vikasana – Bridge Course 2012kea.kar.nic.in/vikasana/bridge/chemistry/chap_09_ppt.pdf · elements and remaining are synthetic elements. Vikasana – Bridge Course 2012. Characteristics

Need for classification of elements:With rapid advance in science, the number of

discovered element increased it is difficult to studyand remember the behavior and properties of eachand every element and also how they form thecompounds hence attempts have been made tocompounds hence attempts have been made toclassify these elements in to groups of elementshaving similar characteristics.

Vikasana – Bridge Course 2012

This method of grouping the elements intoThis method of grouping the elements intodifferent classes is known as periodiccalcification of elements which means the actualcalcification of elements which means the actualor ideal arrangements of those elements whichare alike and separation of those which areare alike and separation of those which areunlike. This classification of elements make asystematic study of elements otherwise itsystematic study of elements, otherwise itbecomes impossible to understand theproperties of elements

Vikasana – Bridge Course 2012properties of elements.

What are Elements ?

Elements are the pure substances containingonly one kind of atoms, which cannot bedecomposed by any physical or chemicalprocess.Chemists have discovered 118 elements sofar. Among these elements, 92 are normalelements and remaining are synthetic

Vikasana – Bridge Course 2012elements.

Characteristics of the elements:

• An element is a pure substance, made up ofl ki d f

C a acte st cs o t e e e e ts

only one kind of atoms.• An atom is smallest unit of an element and

it possesses properties of that elementit possesses properties of that element.• Elements may occur in the free state in

nature or found in the form of theirnature or found in the form of theircompounds.


• Some elements (like radioactive elements)can be prepared artificially by nuclear

tireactions.

• The properties of different elements aredifferent. This is because, the arrangement ofl t ( l t i fi ti ) i telectrons (electronic configuration) in atoms

are different.Vikasana – Bridge Course 2012

The following are the advantages ofg gclassification of elements.

• To study the elements in a systematicmannermanner

• To correlate the properties of elements.• To know the type of different• To know the type of different

compounds that different elements canform

Vikasana – Bridge Course 2012form

Historical background of l ifi ti f l tclassification of element:

E li tt t d t l ifEarlier, an attempt was made to classifythe elements into metals and non-metals.


Metals:Metals:An element is a metal if it has the followingproperties

• It is lustrous i.e. it has shining of surface.It i d d t f h t d l t i it

properties

• It is a good conductor of heat and electricity.• It is ductile i.e. it can be drawn into wires.• It is malleable i.e. it can be beaten into thin sheets.It is malleable i.e. it can be beaten into thin sheets.


• It is solid at room temperature.p• It has a tendency to lose one or more electrons.

Exceptions:Mercury and Gallium are liquids at room

temperature Zinc is not malleable and ductiletemperature. Zinc is not malleable and ductile.


Table: 1 List of common metalsSlNo.

Name in English

Name in other Language

Symbol

1 LithiumLithium -- LiLi2 Sodium Natrium (Latin)Natrium (Latin) NaSod u N u ( )N u ( ) N3 Magnesium - Mg

4 Aluminum - Al

5 Potassium Kalium (Latin) KVikasana – Bridge Course 2012

5 Potassium Kalium (Latin) K

Sl Name in Name in otherSlNo.

Name in English

Name in other Language Symbol

6 Calcium - Ca6 Calcium - Ca7 Vanadium - V8 Ch i C8 Chromium - Cr9 Manganese - Mn10 Iron Ferrm (Latin) Fe


Sl Name in Name in other SymNo. English Language

ybol

11 Cobalt - Co11 Cobalt - Co12 Nickel - Ni13 Copper Cuprum (Latin) Cu14 Zinc - Zn14 Zinc Zn15 Gallium - Ga


Sl Name in Name in otherSlNo.

Name in English

Name in other Language Symbol

16 Silver Argentums (Latin) Ag16 Silver Argentums (Latin) Ag17 Tin Stannum (Latin) Sn18 Barium - Ba19 Platinum - Pt20 Gold Aurum (Latin) Au


Sl Name in Name in other SymbolNo. English Language

y

21 Mercury Hydrargyrum (Latin) Hg21 Mercury Hydrargyrum (Latin) Hg22 Lead Plambun (latin) Ph23 R di R23 Radium - Rq24 Uranium Wolfram (German) U25 Tungsten - W26 Thorium - Th

Vikasana – Bridge Course 201226 Thorium Th

Non – Metals :•An element is a non-metal if it has thefollowing properties.• It has no luster.• It is a bad conductor of heat and electricity.• It is not ductile.• It is not malleable• It has a tendency to gain one or more electrons.• It is a liquid or gas or a brittle solid at room

Vikasana – Bridge Course 2012• It is a liquid or gas or a brittle solid at room

temperature.

Table: 2 : List of common non-metals.

Sl No. Name Symbol Formula1 Hydrogen H H2

2 Nitrogen N N2g3 Oxygen O O2

4 Fl i F F4 Fluorine F F2

5 Chlorine Cl Cl2


Sl No. Name Symbol Formula6 Bromine Br Br2

7 Iodine I I27 Iodine I I2

8 Carbon C C9 Phosphorus P P4

10 Sulphur S S810 Sulphur S S8

11 Silicon Si SiVikasana – Bridge Course 2012

Disadvantages of classifying the elementsDisadvantages of classifying the elements into metals and non metals.• There is no justification for more active

metals or non metals.• There are some elements which have

properties of metals and non metal suchproperties of metals and non-metal, such elements are known as Metalloids.


Examples of Metalloids1 Boron (B)1. Boron (B)2. Silicon (Si)

G i (G )3. Germanium (Ge)4. Arsenic (As) 5. Antimony (Sb)6 Tellurium (Te)6. Tellurium (Te)7. Polonium (Po)

A t ti (At)Vikasana – Bridge Course 20128. Astatine (At)

Dobernier’s triads:After the development of atomic theory and

d i i f h i f l

Dobernier s triads:

determination of the atomic masses of a largenumber of elements, attempts were made toclassify the elements on the basis of atomicmass. Dobernier was the first to correlate thess. obe e w s e s o co e e eproperties of elements with their atomicmasses

Vikasana – Bridge Course 2012masses.

In 1817 Dobernier classified theIn 1817, Dobernier classified theelements into group of three elementssuch that the three elements had similarsuch that the three elements had similarproperties and the atomic mass of the

iddl l t th ith timiddle element was the arithmetic meanof the atomic masses of the first and thethird elements. The group of such threeelements was called Triads.


Dobernier’s Triads:Dobernier s Triads:

Elem Atomic Eleme Atomic Eleme AtomicElement

Atomic Mass

Element

Atomic Mass

Element

Atomic Mass

Li 7 C 40 Cl 35 45Li 7 Ca 40 Cl 35.45Na 23 Sr 88 Br 80K 39 Ba 137 I 127


At. mass of Na = At.mass of Li + At. Mass of K2

= 7+39 = 46 = 232 2

At. mass of Sr = At.mass of Ca + At. Mass of BaAt. mass of Sr At.mass of Ca At. Mass of Ba2

= 40+137 = 177 = 88 2 2

Vikasana – Bridge Course 20122 2

Disadvantages of Dobernier’s triads.

It t ibl t ll l t• It was not possible to group all elements into triads.

• The elements with dissimilar properties were grouped as triads.


l C b i OElement Carbon Nitrogen OxygenAt Mass 12 14 16At Mass 12 14 16

At f N At f C At M f OAt. mass of N = At.mass of C + At. Mass of O2

12 16 28 14= 12+16 = 28 = 14 2 2


Newland’s Classification:

In 1863, J.A. Newland observed thatwhen elements are arranged in thewhen elements are arranged in theincreasing order of their atomicmasses,


He observed thatHe observed that1. Every eighth element was similar in properties to firstone.2. All elements are constituents of complex system.3. Properties of elements change with their atomicweights.g4. There is a recurrence of properties at fixed intervalsi.e. properties of elements repeated at every eighthelement similar to repetition of musical notes in anelement, similar to repetition of musical notes in anOctave. Newland called this as Law of Octaves.


l iElement Li Be B C N O FAt. Mass 7 9 11 12 14 16 19Element Na Mg A Si P S ClAt. Mass 23 24 27 28 31 32 35.45t. ass 3 7 8 3 3 35. 5Element K CaAt Mass 39 40At. Mass 39 40


• The eighth element from lithium is sodium, eighthelement from sodium is potassium, thereforeLithium, sodium and potassium have similar

• Similarly eighth element from beryllium is magnesium,

properties.

Similarly eighth element from beryllium is magnesium,eighth element from magnesium is calcium, therefore,beryllium, magnesium and calcium have similarproperties. However this did not hold good beyond Ca.


Advantages of Newland’s fclassification.

At i f th l t• Atomic mass of the element wasconsidered as basis of classification.

• It explains periodicity in the properties ofelementselements.


Disadvantages of Newland’s classification.

Th b ti d b N l d d•The observation made by Newland does not hold good beyond Ca.•Transition elements were not considered for Octaves.•There was no proper place for hydrogen.


Lothar Meyer’s Graph: Lothar Meyer (1869) tried to classifyLothar Meyer (1869) tried to classify

the elements by plotting a graph of atomicvolume versus atomic masses of differentvolume versus atomic masses of differentelements. Similar elements occupiedsimilar positions in the graphsimilar positions in the graph.


Mendeleev’s Classification: The classification ofelements made by Newland on the basis of atomicelements made by Newland on the basis of atomicmass was continued by Mendeleev. He observedthat when elements are arranged in the increasingorder of their atomic masses, the properties of theelements repeated at certain intervals. He gave hisobservation in the form of a law known asobservation in the form of a law, known asMendeleev’s periodic law. It states that theproperties of the elements are periodic functions ofproperties of the elements are periodic functions oftheir atomic masses.


Wh M d l d thWhen Mendeleev arranged theelements in the increasing order of theiratomic masses, the elements with similarproperties were placed in the samep p pcolumn, and a table was prepared. It isknown as Mendeleev’s periodic tableknown as Mendeleev s periodic table.


A periodic table is a chart representing thesystematic arrangement of elements intosystematic arrangement of elements intovertical columns and horizontal rows suchth t l t ith i il ti f ll ithat elements with similar properties fall inthe same column.


Characteristics of Mendeleev’s periodictable:• The vertical columns in the periodic table are

called groups. There are 8 groups.

table:

called groups. There are 8 groups.• These are numbered as I, II, III, IV, V, VI,VII & VIIIVII & VIII.• Each of group from I & VII were dividedinto subgroups a & b Thus there were 15into subgroups a & b. Thus, there were 15vertical columns that constituted 8 groups.


•The horizontal rows in the periodic tableare called periods.p• There is gradual change in the property

f El t f t lli t t lliof Elements from metallic to non-metallicalong the period from left to right.


Advantages of Mendeleev’s periodic table:• It is based on atomic mass of the element

which is considered as fundamental property ofwhich is considered as fundamental property ofelement.• The elements with similar properties fall in thesame group.• There is repetition in the properties of elementst t i i t l Thi i k i di itat certain intervals. This is known as periodicity

in the properties of elements. Thus it explainsperiodicity in the roperties of elements

Vikasana – Bridge Course 2012periodicity in the roperties of elements.

• Some gaps were left for undiscoveredSome gaps were left for undiscoveredelements. The properties of undiscoveredelements were predicted by Mendeleev onp ythe basis of other elements in the samegroup.

• Mendeleev corrected the atomic massus of some elementsof some elements.


Di d f M d l ’ i di blDisadvantages of Mendeleev’s periodic table.• Position of Hydrogen:Position of Hydrogen:

There was no proper position forhydrogen atom It is placed in Ib and VIIb inhydrogen atom. It is placed in Ib and VIIb inoriginal Mendeleev’s periodic table.


• Anomalous pairs:In Mendeleev’s periodic table, the

elements are arranged in the increasingg gorder of their atomic masses but some pairsof elements were placed such that elementspwith higher atomic masses were placedprior to those with lower atomic masses.pEg. Cobalt 58.9 Nickel 58.6

Tellurium 128 Iodine 127Vikasana – Bridge Course 2012

• Position of rare earth elements & actinides:The position of rare earth elements &

actinides cannot be justified on thejbasis of atomic masses.• Position of isotopes:

Isotopes are the atoms of the sameelements with different atomic mass & sameatomic number. They have similarproperties but the position of isotopescannot be j stifiedVikasana – Bridge Course 2012cannot be justified.

•Position of transition elements:According to Mendeleev, elements of

only VIII group are the transition elements. y g pThis is not justified.

• Superfluous relationships : ElementsSuperfluous relationships : Elements with different properties are placed in same groupgroup.a. Alkali metals with copper, silver and gold in group Ib b Fluorine and manganese in group VIIa

Vikasana – Bridge Course 2012group Ib b. Fluorine and manganese in group VIIa

Mendeleev’s period table of elements (1869)Groups I II III IV V VI VII VIII

Sub Groups a b a b a b a b a b a b a b1 H H

1 12 Li Be B C N O F

7 9 11 12 14 16 193 Na Mg Al Si P S Cl

23 24 27 28 31 32 35.54 K Ca Ti V Cr Mn Fe Co Ni

39 40 48 51 52 55 56 58.9 58.65 Cu Zn Ar Se Br

63 65 75 79 806 Rb Sr Yt Zr Nb Mo Ra Rh Pd

86 88 89 91 93 96 101 103 1067 Ag Cd In Sn Sb Te I

108 112 113 122 122 128 1278 Cs Ba Ce

133 137 1409

10 Fr La Ta W OS Ir Pt167 181 181 184 190 192 195

Vikasana – Bridge Course 201211 As Hg Tl Pb Bi

197 201 204 207 20912 - Tb U

232 238

Groups I IIGroups I IISub Groups a b a b

1 H11

2 Li Be7 9

3 Na Mgg23 24

4 K Ca39 40

5 Cu Zn63 65

6 Rb Sr86 8886 88

7 Ag Cd108 112

8 Cs BaVikasana – Bridge Course 2012

8 Cs Ba133 137

9 As Hg197 201

Modern Periodic Table:In 1918, H.G.I. Moseley showed by X-ray analysis that theatomic number is a better fundamental property of an

Modern Periodic Table:

element than its atomic mass, therefore he classified theelements based on atomic number. He proposed hisobservation in the form of a law known as Modern periodicplaw. It states that the physical and chemical properties of allelements are periodic functions of their atomic number.


Based on this, elements were classifiedand a periodic table was prepared It consists ofand a periodic table was prepared. It consists of7 periods and 18 groups. The significance ofthe modern periodic table is that the propertiesthe modern periodic table is that the propertiesof the elements depend on the arrangement ofthe electrons (electronic configuration) of their( g )atoms. It is observed in the periodic table thatthe elements with similar electronic

fi i f ll i h Thconfiguration fall in the same group. Thesimilar properties of the elements repeat insome intervals

Vikasana – Bridge Course 2012some intervals.

This is known as periodicity in theThis is known as periodicity in theproperties of the elements. This is due torepetition of similar electronic configuration ofl i h i l h f ll ielements in the same interval. The following

are the periodic properties of the elements1 Atomic radius1. Atomic radius.

1. 2. Ionisation energy.2 3 Electronegativity2. 3. Electronegativity.3. 4. Electron affinity.


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Vikasana – Bridge Course 2012kea.kar.nic.in/vikasana/bridge/chemistry/chap_09_ppt.pdf · elements and remaining are synthetic elements. Vikasana – Bridge Course 2012. Characteristics