class 11 classification of elements- important points

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