The document provides an overview of the periodic classification of elements. It discusses early attempts at classification including Dobereiner's triads and Newlands' law of octaves. It then covers Mendeleev's periodic table, including its merits and defects. Finally, it describes the modern periodic table based on atomic number, including periodic trends in properties like atomic size and electronegativity across periods and down groups. Key topics covered include the groups and periods in the modern table, how to read and understand its layout, and common questions about periodic trends and properties.

1. Chapter- 5
PERIODIC
CLASSIFICATION
OF ELEMENTS
10th SCIENCE

2. 2
Wel Come
Presenting:
SHASHIKUMAR B.S.
GHS, ELEKYATHANAHALLI
NELAMANGALA TQ,
BENGALURURU RURAL DIST.

3. Why do we need classification ?

4. Which group these belongs to?

5. Learning points:
• Dobarainers Triads
• Newland’s octaves
• Mendeleev's Periodic table
• Merits and demerits of
Mendeleev's periodic table
• Modern periodic table
• Periodic trends

6. • The arranging of elements into different
groups on the basis of the similarities in
their properties is called classification of
elements.
• The classification of similar elements into
groups makes the study of elements
easier.
• There are about 118 different elements
known so far.
• 94 naturally occurring and 24 artificially
synthesized
Classification of elements :-

7. The earliest attempt to classify
elements was grouping the then
known elements (about 30 elements)
into two groups called metals and
non metals.
The defect in this classification was
that it had no place for metalloids
(elements which have properties of both
metals and non metals) which were
discovered later.
Early attempts at classification
of elements

8. Dobereiner’s Triads -
Dobereiner classified elements in
the increasing order of their
atomic masses into groups of
three elements called triads.
In each triad the atomic mass of
the middle element was
approximately equal to the
average atomic mass of the
other two elements.

9. Dobereiner’s Triads -
𝑨 = 𝟐𝐁 − 𝐂
𝐂 = 𝟐𝐁 − 𝐀
Consider A,B and C are the three
elements.
According to Dobereiners’ triads,
we can calculate the atomic mass
of the middle element by using the
formula 𝐁 =
𝐀+𝐂
𝟐

10. Dobarainers triads:

11. Dobereiner’s Triads -
The defect in this
classification was that all the
then known elements could
not be correctly arranged
into triads.

12. Newlands law of octaves
• John Newlands, an English scientist.
• He was 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’
• He found that
“every eighth element had properties
similar to that of the first”

13. Newlands’ Octaves
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 - -

14. Characteristics of Newlands’
Law of Octaves
• It contained the elements
from hydrogen to thorium
• Properties of every eighth
element were similar to
that of the first element

15. Limitations of Newlands
octaves
•The law was applicable to
elements up to calcium (Ca) only
•It contained only 56 elements.
•He was assumed that only 56
elements existed in nature and no
more elements would be discovered
in the future.

16. Limitations of Newlands octaves
• In order to fit elements into the table.
Newlands’ adjusted two elements in the
same slot and also put some unlike
elements under same note.
• For example cobalt and nickel are in the
same slot and these are placed in the
same column as fluorine, chlorine and
bromine which have very different
properties than these elements.
• Iron, which resembles cobalt and nickel
in properties, has been placed differently
away from these elements

17. Mendeleev’s periodic law :-
The main credit for classifying
the elements goes to
Dmitri Mendeleev, a Russian
chemist.
He stated that. .
‘ The properties of elements
are periodic functions of
their atomic masses’.

18. Mendeleev’s periodic table :-

19. Mendeleev’s periodic table :-
Mendeleev’s periodic table has
6 horizontal rows called periods and
8 vertical rows called groups.
The groups 1 to 7 had two sub groups
called A sub group and B sub group.
Group 8 had 3 rows of elements.
Elements having similar properties
were placed in the same groups.
There are some spaces left vacant in
the table to accommodate the elements
to be discovered in future..

20.  Elements were classified on a more
fundamental basis of their atomic
masses and properties.
 Spaces were left vacant to accommodate
the elements to be discovered in future.
 It could predict the properties of the
elements which helped in the discovery
of new elements.
 The inert gas elements discovered later
could be placed in a separate group
without disturbing the table.
Merits of Mendeleev’s periodic table :-

21.  The speciality of Mendeleevs periodic
table is that what he was predicted and
leave the space for the future discovering
elements, they discovered in his life time
only and their properties were similar to
Mendeleev’s predictions.
Example:
 Eka Boran – Scandium
 Eka Aluminium – Gallium
 Eka silicon - Germanium
Merits of Mendeleev’s periodic table :-

22. Merits of Mendeleev’s periodic table :-

23.  Some elements are not arranged in
the increasing order of their atomic
masses.
 Co is placed before Ni, Te is placed
before I etc.
Defects of Mendeleev’s periodic table :-

24.  Position of hydrogen is not
clear because it shows
properties similar to
metals as well as non
metals.
 The position of isotopes of
elements is not clear.
Defects of Mendeleev’s periodic table :-

25. Henry Moseley a English physicist gave a
new property of elements, ‘atomic
number’ and this was adopted as the
basis of Modern Periodic Table’.
Modern periodic table

26. Modern Periodic Law:
“Properties of elements are a
periodic functions of their atomic
number"
Modern periodic table
Accordingly, Mendeléev’s Periodic Law
was modified and atomic number was
adopted as the basis of Modern Periodic
Table and the Modern Periodic Law can
be stated as

28. How to read and understand the
periodic table :-

30. The modern periodic table consists
of 18 groups and 7 periods
 Vertical columns are Groups and
horizontal lines are called Periods
Elements present in any one
group have the same number of
valence electrons.
Also, the number of shells
increases as we go down the
group.
Position of elements in Modern
Periodic Table:

31. Elements present in any one
period, contain the same number
of shells.
Also, with increase in atomic
number by one unit on moving
from left to right, the valence
shell electron increases by one
unit
Each period marks a new
electronic shell getting filled
Position of elements in Modern
Periodic Table:

32. Modern periodic table :-
There are 7 periods of elements as follows :-
 First period has 2 elements H and He called
very short period.
 Second period has 8 elements Li to Ne
 Third period has 8 elements Na to Ar
 Fourth period has 18 elements K to Kr
called long period.
 Fifth period has 18 elements Rb to Xe
 Sixth period has 32 elements Cs to Rn
 Seventh period has 32 elements from
Fr to atomic number 118 called
incomplete period.

33. Modern periodic table :-
 The 14 elements each of he sixth
and seventh periods are placed
separately at the bottom of the
table.
 The 14 elements of the sixth period
from La to Lu are called Lanthanides.
 The 14 elements of the seventh period
from Ac to Lr are called Actinides.

34. Groups :-
There are 18 groups .
Group 1 elements are called alkali metals
Group 2 elements are called alkaline
earth metals.
Group 17 elements are called halogens.
Group 18 (0 group) are called noble gases.

35. Groups :-
In a group all the elements have the
same number of valence electrons
 Group I elements have 1 valence
electron,
Group II elements have 2 valence
electron
Group III elements have 3
valence electrons etc.
 In a period all the elements
contain the same number of
shells.

36. Valency:
The valency of an
element is determined by
the number of valence
electrons present in the
outermost shell of its
atom.
Trends in the modern periodic table

37. Valency :-
In a period the valency of the elements increases from 1 to
4 and then decreases from 4 to 0 from the left to the right.
Valence electrons - 1 2 3 4 5 6 7 8
Valency - 1 2 3 4 3 2 1 0
In a group the valency is the same for all
elements of the group.
Eg :- Group – I
Elements AN EC VE Valency
H 1 1 1 1
Li 3 2,1 1 1
Na 11 2,8,1 1 1
K 19 2,8,8,1 1 1
Elements - Li, Be, B, C, N, O, F, Ne
Eg :- 2nd Period

38. Atomic size
The term atomic size refers to the radius of
an atom.
The atomic size may be visualised as the
distance between the centre of the nucleus
and the outermost shell of an isolated
atom.
Across the period from left to right atomic
size decreases, because electrons are
added to the same shell
Down the group atomic size increases
because, as we go down the group shells
no. increases

39. Atomic size

41. Metallic property (Electropositive nature)
Some elements tend to lose electrons
while forming bonds, that is, they are
electropositive in nature (+).
All metals donate their outer most
electrons during chemical reaction,
and becomes electropositive (+)

42. Metallic property (Electropositive nature)

43. Non metallic property (Electronegative nature)
Some elements tend to gain
electrons while forming bonds,
that is, they are electro negative
in nature (-).
All non metals (except Hydrogen)
receive electrons during chemical
reaction, and becomes
electronegative (-)

44. Non metallic property (Electronegative nature)

45. Trends in periodic table

46. Trends in periodic table
Trends Across the
period from
left to right
Down the
group
Atomic size Decreases increases
Electro
positivity
Decreases increases
Electro
negativity
Increases decreases
Metallic
nature
Decreases increases
Non metallic
nature
Increases decreases

47. Some important questions
• State the Dobereiners law of triads,
newlands octaves, mendeleevs
periodic law and modern periodic law
• Observe the periodic table given
below and identify the any three pairs
of Dobereiners triads.

48. Some important questions
• Three elements X, Y and Z belong to 17th group
but 2nd, 3rd and 4th period respectively.
Number of valence electrons in Y is 7. Find the
number of valence electrons in X and Z.
* The atomic number of elements A, B, C, D and E
are given below :
Element A B C D E
Atomic no. 7 10 12 4 19
(i) Which two elements are chemically similar ?
(ii) Which is an inert gas ?
(iii) Which element belongs to 3rd period of
periodic table ?
(iv) Which element among these is a non-metal ?

49. Some important questions
• What are periods and groups with respect to
modern periodic table?
• Table given below shows a part of the
periodic Table Using this table explain why?
(a) Li and Na are considered as active metals.
(b) Atomic size of Mg is less than that of Na.
(c) Fluorine is more reactive than chlorine.
H He
Li Be B C N O F Ne
Na Mg Al Si P S Cl Ar

50. Some important questions
• **** Give reason why noble gases are
placed in separate group in modern
periodic table?
• How does the electronic configuration of
an atom of an element related to its
position in the modern periodic table ?
Explain with one example.
• Write the formula of chlorides of Eka-
silicon and Eka-aluminium, the elements
predicted by Mendeleev.

51. Some important questions
• **** How does the tendency of the
elements to lose electrons change in the
Modern Periodic Table in (i) a group, (ii)
a period and why ?
• Arrange the following elements in the
descending order of atomic size and give a
reason for your answer. Mg, Cl, P, Ar.
(Atomic numbers of the above elements are 12, 17,
15, 18 respectively)

52. Some important questions

53. 53
Thank you
Presenting:
SHASHIKUMAR B.S.
GHS, ELEKYATHANAHALLI
NELAMANGALA TQ,
BENGALURURU RURAL DIST.