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MODERN PERIODIC TABLE

The modern long form of periodic table was constructed by Neils Bohr based on modern periodic law proposed by Moseley.

LONG FORM OF MODERN PERIODIC TABLE
GROUPS
s-block d-block           p-block
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
IA IIA IIIB IVB VB VIB VIIB VIII IB IIB IIIA IVA VA VIA VIIA 0
ns1 ns2np6
P
E
R
I
O
D

S

1 1H ns2 ns2np1 ns2np2 ns2np3 ns2np4 ns2np5 2He
2 3Li 4Be 5B 6C 7N 8O 9F 10Ne
3 11Na 12Mg (n-1)d1-10 ns1-2 13Al 14Si 15P 16S 17Cl 18Ar
4 19K 20Ca 21Sc  22Ti 23V 24Cr 25Mn 26Fe 27Co 28Ni 29Cu 30Zn 31Ga 32Ge 33As 34Se 35Br 36Kr
5 37Rb 38Sr 39Y 40Zr 41Nb 42Mo 43Tc 44Ru 45Rh 46Pd 47Ag 48Cd 49In 50Sn 51Sb 52Te 53I 54Xe
6 55Cs 56Ba 57-71  72Hf 73Ta 74W 75Re 76Os 77Ir 78Pt 79Au 80Hg 81Tl 82Pb 83Bi 84Po 85At 86Rn
7 87Fr 88Ra 89-103  104Rf 105Db 106Sg 107Bh 108Hs 109Mt 110Ds 111Rg 112Cn 113Uut 114Fl 115Uup 116Lv 117Uus 118Uuo
  f-block
Lanthanoids 57La 58Ce 59Pr 60Nd 61Pm 62Sm 63Eu 64Gd 65Tb 66Dy 67Ho 68Er 69Tm 70Yb 71Lu
Actinoids 89Ac 90Th 91Pa 92U 93Np 94Pu 95Am 96Cm 97Bk 98Cf 99Es 100Fm 101Md 102No 103Lr

 

MODERN PERIODIC LAW

The modern periodic law was proposed by Moseley. He found the relation between atomic numbers (Z) and the frequencies (ν) of X-rays produced when the atoms of different elements are bombarded with cathode rays. The relation between the square root of frequency (√ν) of highest energy emission line, called Kα line, with the atomic number, Z was found to be linear. 

The mathematical relation can be presented as:

νa(Z-b)

Where a & b are constants, characteristic of elements.

Later on it was clearly established that an element can be characterized by its atomic number, Z and not by the atomic weight. It was also found that there is a relation between electronic configuration and properties of elements. The number of electrons in an atom and its electronic configuration are in turn are related to the atomic number. 

Thus the modern periodic law can be stated as: 

"The chemical and physical properties of elements are the periodic functions of their atomic numbers and electronic configurations."

The modern long form of periodic table was constructed based on above law. The following points are considered while constructing the periodic table.

* The elements in the periodic table are arranged in the increasing order of the atomic number.

* Every row, also called as period, in the periodic table starts with the filling up of differentiating electron into a new quantum shell.

* The elements in a vertical column called as group should get similar outer electronic configuration since it is observed that the elements with similar outer electronic configuration show similar chemical properties. 

 

SALIENT FEATURES OF LONG FORM OF MODERN PERIODIC TABLE

The long form of modern periodic table consists of seven rows called periods and eighteen columns called groups

Periods: 

* Each period starts with an alkali metal and ends with an inert gas element. 

* The first period is a very short period with only two elements i.e., Hydrogen (H) & Helium (He). In this period, the 1s orbital is being filled up.

1 1H 2He

 

* The second period starts with Lithium (Li) and ends with Neon (Ne) and contains 8 elements. It is called first short period. In this group, the 2s & 2p orbitals are being filled up.

2 3Li 4Be 5B 6C 7N 8O 9F 10Ne

 

* The third period also contain 8 elements i.e., from Sodium (Na) to Argon (Ar). It is called second short period. The 3s & 3p orbitals are being filled up in this period.

3 11Na 12Mg 13Al 14Si 15P 16S 17Cl 18Ar

 

* The fourth period is the first long period with 18 elements, it starts with Potassium (K) and ends with Krypton (Kr). It also includes 10 elements belonging to 3d series i.e., from Scandium (Sc) to Zinc (Zn). In this period, not only 4s & 4p and also the 3d orbitals are being filled up by electrons.

4 19K 20Ca 21Sc  22Ti 23V 24Cr 25Mn 26Fe 27Co 28Ni 29Cu 30Zn 31Ga 32Ge 33As 34Se 35Br 36Kr

 

* The fifth period is the second long period with 18 elements, it starts with Rubidium (Rb) and ends with Xenon (Xe). It also includes 10 elements belonging to 4d series i.e. from Yttrium (Y) to Cadmium (Cd). The 5s & 5p along with 4d orbitals are filled up by electrons.

5 37Rb 38Sr 39Y 40Zr 41Nb 42Mo 43Tc 44Ru 45Rh 46Pd 47Ag 48Cd 49In 50Sn 51Sb 52Te 53I 54Xe

 

* The sixth period is the longest period with 32 elements. It not only includes 10 elements belonging to 5d series i.e., Lanthanum (La), Hafnium (Hf) to Mercury (Hg) but also contains 14 elements belonging the 4f series called lanthanides (Cerium (Ce) to Lutetium (Lu)). 

In this period, the 6s & 6p along with 4f & 5d orbitals are being filled up.

6 55Cs 56Ba 57-71  72Hf 73Ta 74W 75Re 76Os 77Ir 78Pt 79Au 80Hg 81Tl 82Pb 83Bi 84Po 85At 86Rn
Lanthanoids 57La 58Ce 59Pr 60Nd 61Pm 62Sm 63Eu 64Gd 65Tb 66Dy 67Ho 68Er 69Tm 70Yb 71Lu

 

Note: Lanthanum is also considered to be the part of f-block since its properties resemble more to lanthanoids.

* The seventh period is an incomplete period. It starts with Fr. It also includes the 14 elements belonging to 5f series called actinides (Thorium (Th) to Lawrencium (Lr)). 

In this period, the 7s & 5f orbitals are filled up. Until recently this period is considered to be incomplete. The names of some of its elements are not yet finalized (like Uut, Uup etc.)

7 87Fr 88Ra 89-103  104Rf 105Db 106Sg 107Bh 108Hs 109Mt 110Ds 111Rg 112Cn 113Uut 114Fl 115Uup 116Lv 117Uus 118Uuo
Actinoids 89Ac 90Th 91Pa 92U 93Np 94Pu 95Am 96Cm 97Bk 98Cf 99Es 100Fm 101Md 102No 103Lr

Note: Actinium is also considered to be the part of f-block since its properties resemble more to actinoids.

* The Lanthanides and actinides are placed below the periodic table separately.

Groups: 

* The 18 groups in the periodic table are numbered from 1 to 18 according to IUPAC convention. 

However, according to American convention, these are also denoted by IA , IIA, IIIB, IVB, VB, VIB, VIIB, VIII (which actually includes 3 groups), IB ,IIB, IIIA, IVA, VA, VIA, VIIA and 0 (zero). This is based on maximum valency shown by elements in the group.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
IA IIA IIIB IVB VB VIB VIIB VIII IB IIB IIIA IVA VA VIA VIIA 0

 

* The elements of IA to VII A groups i.e., 1, 2, 13, 14, 15, 16 & 17 groups are called as representative elements

* The zero group (or 18th group) elements are called as inert gases or noble gases. This group includes He, Ne, Ar, Kr, Xe and Rn.

* The elements of IIIB to IIB i.e., from groups 3 to 12 are called as transition elements.

* However the Lanthanoids and Actinoids are also considered to be the part of IIIB group (i.e., group 3). These are usually called as inner transition elements.

* The elements present in a group show similar physical & chemical properties since they have similar outer electronic configurations.

 

By Aditya vardhan Vutturi