PERIODIC CLASSIFICATION
 
MODERN PERIODIC LAW
  In 1913, an English physicist MOSELEY, as a result of his work on characteristics X-rays of elements   discovered a fundamental and most accurate relation between chemical properties and atomic number of   elements, known as "Modern periodic law".
  ACCORDING TO THE MODERN PERIODIC LAW:

  1. The chemical and physical properties of elements are the periodic function of their atomic       numbers".

  2. The properties of elements depends upon their electronic configuration which vary with       increasing atomic number in a periodic way".
  The modern periodic law provides a logical and scientific ground for the classification of elements.
LONG FORM OF PERIODIC TABLE
  Periods
  Periodic table is divided into seven horizontal rows of elements. Each row of elements is called   "PERIOD".
  General features of a period
  1- Period number of an element represents number of energy levels in the element. For example,
ELEMENTS
PERIOD
NUMBER OF ENERGY LEVELS
Na (Z=23)
K (Z=39)
Rb( Z=55)
Third
Forth
Fifth
3 (K , L , M)
4 (K , L , M , N)
5 (K , L , M , N , O)
. . .
  1. Atomic size decreases in a period.
  2-Nuclear charge increases in a period.
  3-Ionization potential increases in a period.
  4-Electronegativity increases in a period.
  5-Electropositivity and metallic character decreases in period.
  6-Each period starts with Alkali metal and ends on a Noble gas.
  For example:
  2nd period : Li .................................. Ne
  3rd period : Na ..................................Ar
  7-First element of each period is most reactive (electropositive), and last element is chemically inert.
DESCRIPTION OF PERIODS

First period

  It is the shortest period and it contains only two elements (H and He). This period corresponds to filling   up of K-shell. Electronic configuration of the elements of this period is 1s1 and 1s2

Second period

  It is called first short period and it contains eight elements. This period corresponds to filling up of L-shell.   In this period electrons occupy 2s and 2p orbital. This period contain 2 element of s-block and six from
  p-block

Third period

  It also contains eight elements and is known as second short period. It corresponds to filling up of
  M-shell. It contains 2 s-block and 6 P-block elements. In this period 3s and 3P orbital are being filled.
Fourth period

  It contains 18 elements and is known as first long period. This period corresponds to the filling up of
  N-shell. It contains 2 s-block, 6 P-block and 10 d-block (transition) elements. It start with filling of 4s-   orbital followed by 3d and 4p orbital.

Fifth period

  Fifth period contain 18 elements and is known as 2nd long period. It corresponds to filling up of O-shell. It   starts with the filling of 5S-orbital followed by 4d and 5p orbital.
Sixth period
  Sixth period contains 32 elements and it is the longest period.
  Among 32 elements:
  2 elements of s-block with electronic configuration 6s1 and 6s2.
  6 elements of p-block with electronic configuration 6s2, 6p1 to 6s2, 6p6.
  10 elements of d-block with electronic configuration 6s2, 5d1 to 6s2, 5d10
  14 elements of f-block with electronic configuration 6s2, 5d1, 4f1 to 6s2, 5d1, 4f14.
  In sixth period electrons starts filling 4f-orbital after 5d-orbital accommodate one electron.
Seventh period
  7th period is incomplete period.
  It includes:
  2 elements of s-block with electronic configuration 7s1, 7s2
  10 elements of d-block with electronic configuration 7s2, 6d1 to 7s2, 6d10
  14 elements of f-block with electronic configuration 7s2, 6d1, 5f1 to 7s2, 6d1, 5f14

Groups

  Modern periodic table is divided into eight vertical columns of elements. Each vertical column of elements   is called a "GROUP". The groups of the periodic table are further divided into two sub-groups or families "A   and B". Elements of sub-group "A" are known as Normal elements or Representative elements. While the   elements of sub-group "B" are known as Transition elements. Group numbers is designated by Roman   numbers.

General features of a group are as under

  1-Group number of an element shows the number of electrons in the outermost shell of that element
ELEMENT
NUMBER OF VALENCE ELECTRONS
GROUP
Na
Cl
C
1
7
4
I-A
VII-A
Iv-A
  2-Atomic size increases in group.
  3-Ionization potential of elements decreases down the group.
  4-Electronegativity decreases down the group.
  5-Metallic character increases down the groups.
BLOCKS
  On the basis of valence shell electronic configuration, periodic table is divided into four distinct blocks of   elements.

  1. s-block

  2. p-block

  3. d-block

  4. f-block

S-block elements
  All the elements in which last electron enters "ns" orbital are known as s-block elements.
  Elements of group I-A and II-A belong to s-block.
  Their valence shell electronic is ns1 to ns2.
  All the elements of s-block are very reactive and electropositive in nature.
  S-block elements are good reducing agents.
  They form ionic compounds.
  They are all metals and solid. They are low density metals.
  For example :
  Li (z=3) 1s2, 2s1
  Na (z=11) 1s2, 2s2, 2p6, 3s1
  Be (z=4) 1s2, 2s2
p-block elements

  The elements in which valence electrons enter p-orbital and this orbital is progressively filled are
    called p-block elements.
  Their valence shell electronic configuration is from ns2, np1 to
ns2, np6.
  P-block consists of the elements of group III-A to VIII-A (zero-group).
  They include metals, nonmetals and metalloids.
  There are 30 elements in six sub-groups of p-block.

d-block elements
  The elements in which last electron enters (n-1) d-orbital are called d-block elements or outer transition   elements.
  Valence shell electronic configuration of these elements is ns2, (n-1) d1-10.
  All these elements are metals.There are four series of outer transition elements.
  Fourth series is incomplete.
f-block elements
  The elements in which last electron enters (n-2) f-orbital are called f-block elements or inner transition   elements. Their outer electronic configuration is ns2,(n-1)d1,(n-2) f1-14.f-block elements constitute 2   series of elements.
  (1) lanthanides
  (2) Actinides
Lanthanides
  Elements from Cerium (Ce : Z=58) to lutetium (Lu: Z=71) in the periodic table are known as   "Lanthanides".It is a series of 14 elements occurs in the 6th period.They are all silvery and fairly reactive   metals. Most of their compounds contain M+3 ions. Some other lanthanides are also form M+4 complex   fluorides.They are also   known as "rare earth metals".
LANTHANIDE
SERIES
Ce
58
Pr
59
Nd
60
Pm
61
Sm
62
Eu
63
Gd
64
Tb
65
Dy
66
Ho
67
Er
68
Tm
69
Yb
70
Lu
71
Actinides
  Elements from Thorium (Th : Z=90) to lawrencium (Lw : Z=103) in the periodic table are known as   "Actinides".
   It is a series of 14 elements occurs in the 7th period. All actinides are radioactive elements. Most
   of them have very short half life. They are fairly reactive metals. Most of their compounds contain M+3   ions. Among the heavier elements M+2 state becomes stable. They are also known as "Artificial   elements" as they do not occur naturally. They were discovered as products formed during nuclear   reactions.
ACTANIDE
SERIES
Th
90
Pa
91
U
92
Np
93
Pu
94
Am
95
Cm
96
Bk
97
Cf
98
Es
99
Fm
100
Md
101
No
102
Lr
103
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