The document discusses the history and development of the periodic table. It describes early classification systems by Dobereiner, Newlands, and Meyer that recognized patterns in element properties but had limitations. Mendeleev created the first successful periodic table in 1869 by arranging elements by atomic mass and leaving gaps for undiscovered elements. Moseley established in 1913 that atomic number, not mass, is fundamental; the modern periodic table is based on atomic number.

1. BY: VEENU GUPTA
(PGT CHEMISTRY)
APS RAKHMUTHI

2.  “The periodic table is a tabular
method of displaying the
elements in such a way, that the
elements having similar
properties occur in the same
vertical column or group”.

3.  Increase in the discovery of different
elements made it difficult to organise all that
was known about the elements.
 To study a large number of elements with
ease, various attempts were made. The
attempts resulted in the classification of
elements into metals and non-metals.

4.  Dobereiner’s Triads
 Newland’s law of octaves.

5.  Johann Wolfgang Dobereiner, a German chemist, classified
the known elements in groups of three elements on the basis
of similarities in their properties. These groups were called
triads.This classification is based on the atomic mass.
 According to this, when elements are arranged in order of
increasing atomic masses, groups of three elements, having
similar properties are obtained. The atomic mass of middle
element of the triad being nearly equal to the average of the
atomic masses of the other two elements.
 e.g., atomic masses of Li, Na and K are respectively 7, 23
and 39, thus the mean of atomic masses of I St and 3rd
element is equal to the average of the atomic masses of the
other two elements.

6. Element Atomi
c
mass
Element Atomic
mass
Element Atomic
mass
Lithium(Li) 6.9 Calcium (Ca) 40.1 Chlorine(Cl) 35.5
Sodium(Na) 23 Strontium(Sr) 87.6 Bromine (Br) 79.9
Potassium (K) 39 Barium(Ba) 137.3 Iodine (I) 126.9

7.  It fails to arrange all the known elements in the
form of triads, even having similar properties.
 He could identify only a few such triads and
so the law could not gain importance.
 In the triad of Fe, Co, Ni, all the three elements
have a nearly equal atomic mass and thus does not
follow the above law

8. John Newlands.
Reproduced courtesy of the Library
and Information Centre,
Royal Society of Chemistry.

9.  ‘John Newlands’, an English scientist, arranged the
known elements in the order of increasing atomic
masses and called it the ‘Law of Octaves’. It is known
as ‘Newlands’ Law of Octaves’.
 According to this law “when elements are placed in
order of increasing atomic masses, the physical and
chemical properties of every 8th element are a
repetition of the properties of the first element
weight like the eight note of musical scale.”

10.  It contained the elements from hydrogen to thorium.
 Properties of every eighth element were similar to that of the first element.
 Seeing the word octave applied to this table may lead one to think that Newlands
recognised periods of eight elements with repeating properties, as we do with the modern
periodic table, for example: Li Be B C N O F Ne.
 However, each sequence of Newlands' octaves contain only seven elements. Count the
elements in the columns! In Newlands' day the group 8 (18) rare gas elements, He, Ne, Ar,
Kr & Xe, had not yet been discovered.
 To Newlands, H to F & F to Cl are octaves of eight elements, the eighth element repeating
the properties of the first.
 There are seven notes in a musical octave: A B C D E F G, after which you start again with
A'; similarly for Newlands, seven elements H Li G Bo C N O, then the 8th is F and you start
again. [Note that Newlands treated H as a halogen.]

11. sa
(do)
re
(re)
ga
(mi)
ma
(fa)
pa
(so)
da
(la)
ni
(ti)
H Li Be B C N O
F Na Mg Al Si P S
Cl K Ca Cr Ti Mn Fe
Co and
Ni
Cu Zn Y In As Se
Br Rb Sr Ce and
La
Zr - -

12. sa
(do)
H 1 F 8 Cl 15 Co &
Ni 22
Br 29 Pd 36 I 42 Pt & Ir
50
re
(re)
Li 2 Na 9 K 16 Cu 23 Rb 30 Ag 37 Cs 44 Os 51
ga
(mi)
Be 3 Mg 10 Ca 17 Zn 24 Sr 31 Cd 38 Ba & V
45
Hg 52
ma
(fa)
B 4 Al 11 Cr 19 Y 25 Ce & La
33
U 40 Ta 46 Tl 53
pa
(so)
C 5 Si 12 Ti 18 In 26 Zr 32 Sn 39 W 47 Pb 54
da
(la)
N 6 P 13 Mn 20 As 27 Di & Mo
34
Sb 41 Nb 48 Bi 55
ni
(ti)
O 7 S 14 Fe 21 Se 28 Ro & Ru
35
Te 43 Au 49 Th 56

13.  This classification worked well for lighter
elements only up to Ca.
 This classification gave us a relation between
the properties of the elements and their
atomic masses.
 It was shown by this classification for the first
time that there exists a periodicity in the
properties of the elements.

14.  Law of octaves was applicable only upto calcium (only
for lighter elements). After calcium every eighth
element did not possess the properties similar to that
of the first element.
 This classification failed when the heavier elements
beyond Ca were arranged according to Newland’s law
of octaves.
 Newlands assumed that only 56 elements existed in
nature and no more elements would be discovered in
the future. But later on several new element were
discovered whose properties did not fit into law of
octaves.

15.  (iv) At the time of this law, noble gases were unknown. When
noble gases were discovered, neon (Ne) between F and Na, and
argon (Ar) between Cl and K, it becomes the ninth element and
not the eighth which has the similar properties.
 v) In order to fit elements into his table, Newlands put even two
elements together in one slot and that too in the column of unlike
elements having very different properties.
For example, the two elements cobalt (Co) and nickel (Ni) were
put together in just one slot and that too in the column of
elements like fluorine, chlorine and bromine which have very
different properties from these elements.
 (vi) Iron (Fe) element which resemble elements like cobalt and
nickel in properties, was placed far away from these elements.
 Thus, Newland‟s classification was not accepted.

16. LOTHAR MEYER
(* 19. August 1830 in Varel;)
( † 11. April 1895 in Tübingen)

17.  He was one of the pioneers in developing the first periodic
table of chemical elements. Both Mendeleev and Meyer worked
with Robert Bunsen. He never used his first given name, and was
known throughout his life simply as Lothar Meyer.
 Meyer is best known for his part in the periodic classification of
the elements. He noted, as J. A. R. Newlands did in England, if
each element is arranged in the order of their atomic weights,
they fall into groups of similar chemical and physical properties
repeated at periodic intervals.
 According to him, if the atomic weights were plotted as ordinates
and the atomic volumes as abscissae—the curve obtained a series
of maxima and minima—the most electro-positive elements
appearing at the peaks of the curve in the order of their atomic
weights

18. I II III IV V VI VII VIII IX
B Al In(?) Tl
C Si
Ti Zr
Sn Pb
N P
V
As
Nb
Sb
Ta
Bi
O S
Cr
Se
Mo
Те
W
F Cl
Mn
Fe
Co
Ni
Br
Ru
Rh
Pd
I
Os
Ir
Pt
Li Na K
Cu
Rb
Ag
Cs
Au
Be Mg Ca
Zn
Sr
Cd
Ba

19.  According to this “The physical
and chemical properties of the
elements are the periodic
function of their atomic masses.”

20.  The repetition of properties
of elements after certain
regular intervals is known
as Periodicity of Properties.

21. Dmitri Mendeleev.
Reproduced courtesy of the Library
and Information Centre,
Royal Society of Chemistry.

22.  Dmitri Ivanovich – 5 ’ Mendeleev, a Russian
demist, was the most important contributor
to the early development of a periodic table
of elements wherein the elements were
arranged on the basis of their atomic mass
and chemical properties.

23.  Mendeleev arranged 63 elements known at that time in the periodic table.
According to Mendeleev “the properties of the elements are a periodic
function of their atomic masses.” The elements with similar physical and
chemical properties came under the same groups.
 In the periodic table, the elements are arranged in vertical rows called
groups and horizontal rows called periods.
 There are eight groups indicated by Roman Numerals I, II, III, IV, V, VI, VII,
VIII. The elements belonging to first seven groups have been divided into
sub-groups designated as A and B on the basis of similarities.
 The elements that are present on the left hand side in each group constitute
sub-group A while those on the right hand side form sub-group B. Group VIII
consists of nine elements arranged in three triads.
 There are six periods (numbered 1, 2, 3, 4, 5 and 6). In order to accomodate
more elements, the periods 4, 5, 6 are divided into two halves. The first half
of the elements are placed in the upper left corners and the second half
occupy lower right corners in each box.

24.  Systematic Study Of Elements: The arrangement of elements in
groups and periods made the study of elements quite systematic
in the sense that if properties of one element in a particular group
are known,those of the others can be easily predicted.
 Prediction of new elements and their properties: Many gaps were
left in this table for undiscovered elements. However, properties
of these elements could be predicted in advance from their
expected position. This helped in the discovery of these elements.
The elements silicon, gallium and germanium were discovered in
this manner.
 Correction of doubtful atomic masses : Mendeleev corrected the
atomic masses of certain elements with the help of their expected
positions and properties.

25.  He could not assign a correct position of hydrogen in his periodic table,
as the properties of hydrogen resembles both with alkali metals as well
as with halogens.
 No place could be assigned to isotopes of an element.
 The isotopes of the same element will be given different position if
atomic number is taken as basis, which will disturb the symmetry of the
periodic table.
 The atomic masses do not increases in a regular manner in going from
one elements to the next.
 The properties of elements are periodic functions of their atomic mass.
 It has 8 groups.
 Elements with same properties are placed in different groups like
platinum and Gold
 There were three gaps left by Mendeleev in his Periodic Table.
 No distinction was made between metals and non-metals.
 Transition elements are placed together in Group VIII.
 Inert gases were not known at the time of Mendeleev

26. Henry Gwyn Jeffreys Moseley
(23 November 1887 – 10 August 1915)

27.  Moseley's experiments in X-ray spectroscopy showed directly
from their physics that cobalt and nickel have the different
atomic numbers, 27 and 28, and that they are placed in the
Periodic Table correctly by Moseley's objective measurements
of their atomic numbers. Using atomic number instead
of atomic mass as the organizing principle was first proposed
by the British chemist Henry Moseley in 1913, and it solved
anomalies like this one. Iodine has a higher atomic number
than tellurium - so, even though he didn't know
why, Mendeleev was right to place it after tellurium after all!

28.  When World War I broke out in Western Europe, Moseley left his
research work at the University of Oxford behind to volunteer for the
Royal Engineers of the British Army. Moseley was assigned to the force
of British Empire soldiers that invaded the region of Gallipoli, Turkey, in
April 1915, as a telecommunications officer. Moseley was shot and killed
during the Battle of Gallipoli on 10 August 1915, at the age of 27. Experts
have speculated that Moseley could have been awarded the Nobel Prize
in Physics in 1916, if he had not been killed. As a consequence, the
British government instituted new policies for eligibility for combat duty.

29.  This law was given by Henry Moseley in
1913. It states, “The physical and
chemical properties of the elements are
the periodic function of their atomic
numbers”.
 Modern periodic table is based on
atomic number of elements.

30.  Periodicity may be defined as the repetition
of the similar properties of the elements
placed in a group and separated by certain
definite gap of atomic numbers.
 The cause of periodicity is the resemblance in
properties of the elements is the repetition
of the same valence shell electronic
configuration

31.  Moseley proposed this modern periodic table and according to which
“the physical and chemical properties of elements are periodic
function of their atomic number and not atomic mass.“
 Group: The vertical columns in Mendeleev’s, as well as in Modern
Periodic Table, are called groups.
 Period: The horizontal rows in the Modern Periodic Table and
Mendeleev’s Periodic Table are called periods.
 There are 18 groups and 7 (seven) periods in the Modern Periodic
Table.
 The elements belonging to a particular group make a family and
usually named after the first member. In a group all the elements
contain the same number of valence electrons.
 In a period all the elements contain the same number of shells, but
as we move from left to right the number of valence shell electrons
increases by one unit. The maximum number of electrons that can be
accommodated in a shell can be calculated by the formula 2n2 where
n is the number of the given shell from the nucleus.

33. Name of the
Element
Symbol of
the Element
Atomic
Number
Name of the
Element
Symbol of
the Element
Atomic
Number
Hydrogen H 1 Aluminium Al 13
Helium He 2 Silicon Si 14
Lithium Li 3 Phosphorus P 15
Beryllium Be 4 Sulfur S 16
Boron B 5 Chlorine Cl 17
Carbon C 6 Argon Ar 18
Nitrogen N 7 Potassium K 19
Oxygen O 8 Calcium Ca 20
Fluorine F 9 Scandium Sc 21
Neon Ne 10 Titanium Ti 22
Sodium Na 11 Vanadium V 23
Magnesium Mg 12 Chromium Cr 24

34. Name of
the Element
Symbol of
the Element
Atomic
Number
Name of
the Element
Symbol of
the Element
Atomic
Number
Manganese Mn 25 Strontium Sr 38
Iron Fe 26 Yttrium Y 39
Cobalt Co 27 Zirconium Zr 40
Nickel Ni 28 Niobium Nb 41
Copper Cu 29 Molybdenum Mo 42
Zinc Zn 30 Technetium Tc 43
Gallium Ga 31 Ruthenium Ru 44
Germanium Ge 32 Rhodium Rh 45
Arsenic As 33 Palladium Pd 46
Selenium Se 34 Silver Ag 47
Bromine Br 35 Cadmium Cd 48
Krypton Kr 36 Indium In 49
Rubidium Rb 37 Tin Sn 50

35. Name of the
Element
Symbol of
the Element
Atomic
Number
Name of the
Element
Symbol of
the Element
Atomic
Number
Antimony Sb 51 Gadolinium Gd 64
Tellurium Te 52 Terbium Tb 65
Iodine I 53 Dysprosium Dy 66
Xenon Xe 54 Holmium Ho 67
Cesium Cs 55 Erbium Er 68
Barium Ba 56 Thulium Tm 69
Lanthanum La 57 Ytterbium Yb 70
Cerium Ce 58 Lutetium Lu 71
Praseodymium Pr 59 Hafnium Hf 72
Neodymium Nd 60 Tantalum Ta 73
Promethium Pm 61 Tungsten W 74
Samarium Sm 62 Rhenium Re 75
Europium Eu 63 Osmium Os 76

36. Name of
the Element
Symbol of
the Element
Atomic
Number
Name of
the Element
Symbol of
the Element
Atomic
Number
Iridium Ir 77 Actinium Ac 89
Platinum Pt 78 Thorium Th 90
Gold Au 79 Protactinium Pa 91
Mercury Hg 80 Uranium U 92
Thallium Tl 81 Neptunium Np 93
Lead Pb 82 Plutonium Pu 94
Bismuth Bi 83 Americium Am 95
Polonium Po 84 Curium Cm 96
Astatine At 85 Berkelium Bk 97
Radon Rn 86 Californium Cf 98
Francium Fr 87 Einsteinium Es 99
Radium Ra 88 Fermium Fm 100

37. Name of the
Element
Symbol of
the Element
Atomic
Number
Name of the
Element
Symbol of
the Element
Atomic
Number
Mendelevium Md 101 Darmstadtium Ds 110
Nobelium No 102 Roentgenium Rg 111
Lawrencium Lr 103 Copernicium Cn 112
Rutherfordium Rf 104 Nihonium Nh 113
Dubnium Db 105 Flerovium Fl 114
Seaborgium Sg 106 Moscovium Mc 115
Bohrium Bh 107 Livermorium Lv 116
Hassium Hs 108 Tennessine Ts 117
Meitnerium Mt 109 Oganesson Og 118

38.  The trends observed in some important properties of the
elements in :
 moving down the group (from top to bottom of the table)
and
 across a period (from left to right in a period)

39.  Valency may be defined as the combining capacity of the atom of an
element with atoms of other elements in order to acquire the stable
configuration (i.e. 8 electron in valence shell. In some special cases it is 2
electrons).
 The valency of an element is determined by the number of valence
electrons present in the outermost shell of its atom (i.e. the combining
capacity of an element is known as its valency).
 In Period: On moving from left to right in a period, the valency first
increases from 1 to 4 and then decreases to zero .
Example; valency of 2nd period elements are 0
 In Groups: On moving from top to bottom in a group, the valency
remains same because the number of valence electrons remains the
same. Example: Valency of first group elements = 1
Valency of second group elements = 2.

40.  Atomic size refers to radius of an atom. It also refers to the distance between the centre of
nucleus of an isolated atom to its outermost shell containing electrons.
 The trend of atomic size (radius) in moving from left to right in a period:
On moving from left to right along a period, the atomic number of elements increases
which means that the number of protons and electrons in the atoms increases . As
electrons are added to the same shell so due to the large positive charge on the nucleus,
effective nuclear charge increases and thus the electrons are pulled in more closely to the
nucleus and the size of the atom decreases.
 Example: Size of second period elements: Li > Be > B > C > N > O > F
Point to know: The atomic size of noble gases in corresponding period is largest due to
presence of fully filled electronic configuration (i.e. complete octet).
 The trend of atomic size (radius) in moving down a group: On going down in a group of the
Periodic Table, a new shell of electrons is added to the atoms at every step which causes
more screening of the outermost electron from nucleus. So there is an increase in distance
between the outermost shell electrons and the nucleus of the atom and thus the atomic
size increases
 Atomic size of first group element : Li < Na < K < Rb < Cs < Fr
Atomic size of 17th group elements : F < Cl < Br < I

41.  It is the tendency of an atom to lose electrons. Greater the ease of loss of
electron ,greater will be the metallic character.
 Metallic character ᾳ atomic radii
 In Period: Along the period from left to right, metallic characters
decreases because a tendency to lose electron decreases due to the
increase in effective nuclear charge.
 Metallic character of second period elements: Li > Be > B > C >> N > O > F
In Group: On moving from top to bottom, Metallic character increases
because the atomic size increases due to the decrease in effective
nuclear charge and hence the tendency to lose electrons increases.
First group element : Li < Na < K < Rb < Cs
17th group elements: F < Cl < Br < I

42.  It is tendency of an atom to gain electrons. Greater the ease of
gain of electron ,greater will be the non-metallic character.
 Non-Metallic character ᾳ (1/ atomic radii)
 In Period: Along the period from left to right, non-metallic
character increases because tendency to gain electrons increases
due to increase in nucleus charge.
 Non-metallic character of 2nd period elements :
Li < Be < B < C < N < O < F
 In Group: On moving from top to bottom in a group, non-metallic
character decreases because atomic size increases and tendency to
gain electrons decreases.
 Non-metallic character of 17th period element: F > Cl > Br > I

43.  In metals: Chemical reactivity of metals increases
down the group because tendency to lose electrons
increases.
Example ; Li < Na < K < Rb < Cs (1st group)
 In non-metals: Chemical reactivity of non-metals
decreases down the group because tendency to
gain electrons decreases.
Example: F > Cl > Br > I (17th group)

44.  It is tendency of an element to attract the shared pair of
electrons towards it in a covalently bonded molecule.
 It increases with increase of nuclear charge or decrease in
atomic size.
 Along the period electronegativity increases.
Example ;Li < Be < B < C < N < O < F.
 Down the group electronegativity decreases.
Example ; Li > Na > K > Rb > Cs
F > Cl > Br > I

45.  Metal oxides are basic in nature. Ex. Na2O, MgO etc.
 Non-metal oxides are acidic in nature. Ex. Cl2O7,
SO3, P2O5,
 In the case of metal reactivity, it increases down the
group because of the tendency to lose electrons
increases.
 In the case of non-metal, reactivity decreases down
the group because of the tendency to gain electrons
decreases.

46. Property Valency Atomic Size Metallic
Character
Nonmetallic
Character
Electro-
negativity
Variation in
period
Increases
from 1 to 4
then
decreases to
zero
Decreases Decreases Increases Increases
Reason No. of atomic
shells
remains the
same &
atomic
number
increases by 1
unit.
This is due to
an increase in
effective
nuclear charge
which tends to
pull the
electrons closer
to the nucleus
and reduces
the size of the
atom.
Effective
nuclear
charge
increases in
periods.
Hence
tendency to
lose
electron
decreases.
Effective
nuclear charge
increases as
electron are
added to the
same shell in
periods. Hence
tendency to
gain electron
increases
Effective
nuclear
charge
increases in
periods.
Hence
tendency to
attract the
shared pair
of electron
increases

47. Property Valency Atomic Size Metallic
Character
Nonmetallic
Character
Electro-
negativity
Variation
in group
Remains
same
Increases Increases Decreases Decreases
Reason No. of
atomic
shells
increase
but the
number
of valence
electrons
remains
same
New shells are
being added as we
go down the
group. This
increases the
distance between
the outermost
electrons and the
nucleus so that
the atomic size
increases in spite
of the increase in
nuclear charge.
Effective
nuclear
charge
decreases
and thus
the force of
attraction
between
nucleus and
outermost
electron
also
decreases
Effective
nuclear
charge
decreases.
Hence
tendency to
gain
electron
decreases
Effective
nuclear
charge
decreases.
Hence
tendency
to attract
shared pair
of electron
decreases

48. ATOMIC SIZE INCREASES,
IONISATION ENERGY DECREASES,
ELECROPOSTIVE OR METALLIC CHARACTER INCREASES
ELECTRONEGATIVE CHARACTOR OR NON METALLIC CHARACTER DECREASES
THUS,EFFECTIVE NUCLEAR CHARGE DECREASES BETWEEN NUCLEUS AND OUTERMOST
ELECTRON
NUMB
ER OF ATOMIC SHELLS AND SCREENING EFFECT
ALSO INCREASES ON MOVING DOWN THE GROUP
AS ATOMIC NUMBER INCREASE IN A GROUP

49. ATOMIC SIZE DECREASES,
IONISATION ENERGY INCREASES,
ELECROPOSTIVE OR METALLIC CHARACTER DECREASES
ELECTRONEGATIVE CHARACTOR OR NON METALLIC CHARACTER INCREASES
THUS ,EFFECTIVE NUCLEAR CHARGE INCREASES BETWEEN NUCLEUS AND OUTERMOST
ELECTRON
NUMBER OF ATOMIC SHELL REMAINS SAME AND SCREENING EFFECT DONOT
OCCURS
AS ATOMIC NUMBER INCREASE IN A PERIOD

50. THANKS