The document summarizes the historical development of the periodic table. It discusses early classification attempts by scientists like Dobereiner, Newlands, and Meyer. Mendeleev organized the 63 known elements into the first recognizable periodic table in 1869 based on periodic trends in their properties. Moseley's work on X-ray spectra led to the modern periodic table being arranged by atomic number instead of atomic mass. The periodic table is now understood to result from the periodic repetition of electronic structures as electrons fill different atomic orbitals in shells.

1. SREENANDU
Jr. Faculty for CHEMISTRY
TMCC

2. • Historical development
• Relationship- position and electronic configuration

3. • Periodic table - 118 elements (2017)
• Difficult to study and remember all elements individually
• Classification was necessary
• Using atomic weight attempts started to classify elements

4. • Triads
• Law of octaves
• Lothar Mayer’s Atomic volume curve
• Mendeleev’s Periodic table
• Mosley's modern periodic table

5. • Dobereiner’s suggested that, “the atomic weights of the
middle element was the arithmetic mean of the other
two”.

6. • “If elements are arranged in the increasing order of the
atomic weights, the eighth element starting from a given
one is a kind of repetition of the first”

7. • the atomic volumes of the elements were plotted against
the atomic weight
• Elements with similar properties occupied similar
positions on the curve
• Periodicity in
properties with
atomic number

8. • Periodic law: the properties of elements are periodic
functions of their atomic weight
• Elements arranged in 7 horizontal rows (periods) and
vertical columns ( groups )
• 63 elements were known
• Gaps left for unknown elements
• Properties of these elements predicted on the basis of
periodic law
Eg: Gallium ( Eka aluminium) and Germanium (
Eka silicion)

11. Based on work done by Mosely on characteristic
X-rays produced from different elements
Atomic number is more fundamental property
than atomic mass
Proposed arrangement of elements in periodic
table based on atomic number
Modern periodic law: the physical and
chemical properties of elements are the
periodic functions of their atomic numbers

12. • The periodic repetition is called periodicity.
• If outer electronic configuration of atoms are same then
their properties are same

14. • Electronic configuration: distribution of electrons into
orbitals of an atom
• Location of element in the periodic table indicates its
quantum numbers.
• it helps to predict the chemical, electrical and magnetic
behavior of substance
• The electrons are distributed over different energy level.
These energy levels are called the shell or orbits.
• overall energy of all electrons of an atom remains
minimum for stability of atom

15. • The maximum number of electrons in any main energy
level (shell) is given by, ‘2n2’, where, n is an integer and
represents the “principal quantum number”.
Sl. No.
Energy level or Orbit
(shell)
Principal quantum number
‘n’
Maximum Number of electrons (2n2)
1 K 1 2×12 = 2
2 L 2 2×22 = 8
3 M 3 2×32 = 18
4 N 4 2×42 = 32

16. • The each main shell (energy level) is subdivided into sub
shells. These sub shell are called orbitals. These sub
shells /orbitals are designated by s, p, d, f etc. with
corresponding orbital quantum number
• The maximum electron capacity of sub shells is governed
formula of 2(2l + 1)
Sl. No. Subshell Quantum number (l) Electron capacity of sub shell 2(2l+1)
1 s 0 2(2 × 0+1) = 2
2 p 1 2(2 × 1+1) = 6
3 d 2 2(2 × 2+1) = 10
4 f 3 2(2 × 3+1) = 14

17. “states that in the ground state of
an atom, an electron enters the
orbital with lowest energy first and
subsequent electrons are fed in the
order of increasing energies”

18. • Every orbital in a subshell is singly occupied with one
electron before any one orbital is doubly occupied
• All electrons in singly occupied orbitals have the same
spin.

19. • states that, in an atom or molecule, no two electrons
can have the same four electronic quantum numbers.
• As an orbital can contain a maximum of only two
electrons, the two electrons must have opposing spins.
• This means if one is assigned an up-spin ( +1/2), the
other must be down-spin (-1/2).

20. • Horizontal rows in the periodic table
• The value of ‘n’ in the electronic configuration represent
the period which the element belongs
n = 1 Period 1 K shell
n = 2 Period 2 L shell
n = 3 Period 3 M shell
 Total 7 periods
 Lanthanides are extension of 6th period  4f subshell
 Actinides are extension of 7th period  5f subshell

21. Period Electronic
configuration
Number of elements
1 1s 2
2 2s2p 8
3 3s3p 8
4 4s3d4p 18
5 5s4d5p 18
6 6s4f5d6p 32
7 7s5f6d7p Incomplete (32)

22. Columns of the periodic table
Similar electronic configuration in the outer energy shell
Same number of valence electrons
Similarities in physical and chemical properties

23. s - block
d - block
p - block
f - block

24. • Electrons are filled in s – subshell
• Extreme left in the periiodic table
• General electronic configuration ns1-2
• ns1 – Alkali metals
• ns2 – Alkaline earth metals

25. • Electrons are filled in p – subshell
• Groups 13 – 18
• General electronic configuration ns2 np1-6
• ns2 np6 noble gases
• Group 17 – Halogens ( salt forming )
• Group 16 – Chalcogens ( ore forming )

26. • Electrons are filled in d - orbitals of penultimate shell
• Middle portiion of the table
• Groups 3 – 12
• General electronic configuration - ns1-2 (n-1)d1-10
• Known as transition elements
• All are metals with high M.P and B.P
• Variable oxidation state
• Form colored complexes
• Catalytic properties

27. • Electron enters into f- subshell of the anti-penultimate
shell
• Bottom of the periodic table
• Elements coming after Lanthanum- 14 elements (
Lanthanoids)
• Elements coming after Actinum- 14 elements ( Actinoids)
• General electronic configuration - ns2 (n-1)d1-10(n-2)f1-14
• Known as inner transition elements
• Heavy metals with high M.P and B.P
• Variable oxidation
• Colored complexes
• Elements after uranium are called transuranium