1. CLASSIFICATION OF ELEMENTS AND PERIODICITY IN PROPERTIES of elements-1
BY-
A.P.S. BHADOURIYA
M.Sc. , B.Ed., NET
PGT-CHEMISTRY
K.V. BARABANKI

2. Session Objectives Why do we need classification.?
Dobereniner’s triads
Newlands law of octave
Lother Meyer volume curve
Mendeleev’s periodic table
Modern periodic table
IUPAC nomenculature for elements Z >100

3. During the nineteenth century, chemists began to categorize the elements according to similarities in their physical and chemical properties. The end result of these studies was our modern periodic table.
Lavoisier (1789) classified elements into metals, non-metals, gases and earths.

4. Dobereiner’s triads [ John Dobereiner (1829)]
In 1829, he classified some elements into groups of three, which he called triads. The elements in a triad had similar chemical properties and orderly physical properties.
S.No
Triad
Atomic masses of elements of triad
Arithmetic mean of atomic masses of first and third element 1
Cl,Br,I
35.5, 80, 127 2
= 81.25 2
Li,Na,K
7, 23, 39
7 + 39
= 23 2 3
Ca,Sr,Ba
40,87.5,137
40+137 2
= 88.5
Model of triads

5. Newland’s law of octaves [John Newland (1863)]
In 1863, he suggested that elements be arranged in “octaves” because he noticed (after arranging the elements in order of increasing atomic mass) that certain properties repeated every 8th element.

6. Newland’s law of octaves [John Newland (1863)]
Element
Atomic mass
I II III IV V VI VII
Li Be B C N O F
Na Mg Al Si p S Cl
K Ca
Newland was first to publish the list of elements in increasing order of atomic masses.

7. Lother-Meyer’s atomic volume curve

8. Dmitri Mendeleev
In 1869 he published a table of the elements organized by increasing atomic mass.

9. Mendeleev’s periodic law
The physical and chemical properties of elements are periodic function of their atomic masses.

10. Mendeleev’s periodic table

11. Mendeleev’s periodic table
Only 63 elements were known.
Groups
8 vertical rows.
7 groups were subdivided in A and B.
8th group has 9 elements in the group of
3 each.
Periods
7 horizontal rows.

12. Merits of Mendeleev’s periodic table
Prediction of new elements (Ge, Ga, Sc) 1
Systematic study of elements 2
Correction of atomic mass
(Be, Au, Pt) 3

13. Mendeleev
stated that if the atomic weight of an element caused it to be placed in the wrong group, then the weight must be wrong.
(He corrected the atomic masses of Be, In, and U)
was so confident in his table that he used it to predict the physical properties of three elements that were yet unknown.
After the discovery of these unknown elements between 1874 and 1885, and the fact that Mendeleev’s predictions for Sc, Ga, and Ge were amazingly close to the actual values, his table was generally accepted.

14. Defects of Mendeleev’s periodic table
Position of hydrogen.
Position of isotopes e.g. 1H1, 1H2, 1H3
Anomalous pairs. (Ar and K, Co and Ni, Te and I)

15. Defects of Mendeleev’s periodic table
Chemically dissimilar elements are grouped together. (Cu-IA and Na-IB)
Chemically similar elements are placed in different groups. [Cu (I) and Hg (II)].

16. Do you know?
Mendeleev’s periodic table was published in 1905 when no one had an idea of the structure of an atom.
Mendeleev’s name has been immortalized by naming the element with atomic number 101, as Mendelevium. This name was proposed by American scientist Glenn T. Seaborg, the discoverer of this element, “in recognition of the pioneering role of the great Russian Chemist who was the first to use the periodic system of elements to predict the chemical properties of undiscovered elements, a principle which has been the key to the discovery of nearly all the transuranium elements

17. MODERN PERIODIC LAW AND THE MODERN PERIODIC TABLE
English physicist, Henry Moseley observed regularities in the characteristic X-ray spectra. A plot of f against atomic number (Z ) of the elements gave a straight line and not the plot of f vs atomic mass
He thereby showed that the atomic number is a more fundamental property of an element than its atomic mass.

19. Mendeleev’s Periodic Law was, therefore, accordingly modified.
This is known as the Modern Periodic Law and can be stated as :
The physical and chemical properties of the elements are periodic functions of their atomic numbers.

20. Henry Moseley
In 1913, through his work with X-rays, he determined the actual nuclear charge (atomic number) of the elements*. He rearranged the elements in order of increasing atomic number.
*“There is in the atom a fundamental quantity which increases by regular steps as we pass from each element to the next. This quantity can only be the charge on the central positive nucleus.”
His research was halted when the British government sent him to serve as a foot soldier in WWI. He was killed in the fighting in Gallipoli by a sniper’s bullet, at the age of 28. Because of this loss, the British government later restricted its scientists to noncombatant duties during WWII.

21. Modern periodic table

25. Contains elements arranged in increasing order of atomic numbers.
Features of long form of periodic table
Contains elements arranged in increasing order of atomic numbers.
Explains the position of an element in relation to other elements.
Consists of groups and periods.

26. Features of long form of periodic table
Groups
Vertical column
Total 18. Numbered 1-18 or IA to VII A, IB to VII B, VIII and zero.
Elements in a group have similar but not identical electronic configuration and properties
Periods
Horizontal column
Total 7 numbered from 1 to 7.
Contains 2,8,8,18,18,32 and 28 elements respectively.

27. ELECTRONIC CONFIGURATIONS AND TYPES OF ELEMENTS:
s-,p-,d-,f- Block Elements
On the basis of the nature of sub-shell in which last electron of atom enters, elements are divided into 4 blocks
s-Block Element
p-Block Element
d-Block Element
f- Block Element

28. (s-Block Elements ns1 or ns2
In these elements last electron enters the s-orbital
Electronic configuration:
ns1 or ns2
IA (alkali metals )and
IIA(alkaline earth metals
Groups:
All are metal, low ionisation energy and low
melting and boiling points, electropositive
elements.
compounds are mostly ionic & colourless.

29. Electronic configuration:
(p-Block Elements
In these elements last electron enters the p-orbital
Electronic configuration:
ns2,np1 -6
Groups:
III A to VII A and zero group (group 1-18).
Non-metals, electronegative.
Form covalent compounds.

30. (d-Block Elements
In these elements last electron enters the d-orbital,
Also known as transition metals.
Electronic configuration:
(n-1)d1-10 ns1or2
Groups:
I B to VII B and VIII groups (Gr- 3-12).
Variable valency high melting and boiling point.
Coloured compounds and catalytic property.

31. (f-Block Elements
In these elements last electron enters the f-orbital,
Also known as Inner-Transition Elements
Electronic configuration:
(n-2)f1-14(n-1)d0-1ns2
Present below the periodic table in two rows
Lanthanides-elements after lanthanum
Actinides-elements after actinium.
Have high melting and boiling point.

32. Features of long form of periodic table
Representative elements
s and p block elements .
Transition elements
d-block elements. Valence shell and penultimate
Shell both are incomplete.
Inner Transition elements
f-block elements. Valence shell, penultimate shell antipenultimate shell are incomplete.

33. Features of long form of periodic table
Metals
Present on left hand side of periodic table.
Solid,malleable,ductile and conductors .
Non-metals
Present on right hand side of periodic table.
Solid or liquid or gas.
Metalloids
Present on zig-zag between metals and non-metals.
e.g. B,Si,Ge,As,Sb and Te.

34. Merits of long form of periodic table
Based on a more fundamental basis - the atomic number
Position of an element is related to the electronic
configuration of its atom.
Due to separation of elements into groups, dissimilar elements (e.g. alkali metals I A and coinage metals I B) do not fall together.

35. Defects of long form of periodic table
It is unable to include lanthanides and
actinides in its main body.
The problem of the position of hydrogen in
the table has not been solved completely
Configuration of Helium(1s2 ) is different
from inert gases (ns2,np6) but are placed in
the same group.

36. Nomenclature of the elements with atomic number >100
Digit
Name
Abbreviation
nil n 1 un u 2 bi b 3
tri t 4
quad q 5
pent p 6
hex h 7
sept s 8
oct o 9
enn e
Name
=digits name + ium
e.g. atomic number 115
Will be named as un+un+pent+ium
=ununpentium
and symbol is Uup