Modern periodic table
• In modern periodic table 118 elements are present. In which 92 are naturally occurring and 26 are man made elements.
• Periodic table is a tabular form arrangement of elements in the increasing order of their atomic number.
• The modern periodic table is discovered by scientists ‘Henry Mosley ‘ in 1913.
1) Firstly in 1817 the’ Wolfgang Dobereiner ‘ tried to arranged elements of similar properties.
He arrange 3 element in a group by their decreasing order of atomic mass . This arrangement is called Doebereiners triads’
Due to improper arrangement it is rejected
2) After that in 1866 the English scientists ‘Newlands’ arranged the known elements by their increasing order of atomic mass.
He arranged eight element of same properties in a group it is called ‘ Newlands law of octaves ‘
Newlands failed to explain the properties of elements
3) The rejection of Newlands law of octaves.
• The Russian chemist ‘ Mendeleev ‘arrange the known 63 elements on the basis of increasing atomic mass of element , chemical and physical properties of elements.
• Mendeleev created periodic law The law states that ‘ the properties of elements are the
periodic function of their atomic masses’
• Mendeleev periodic table contains vertical ( column) and horizontal rows ( periods)
Due to the limitations Mendeleev periodic table also rejected.
4) Finally in 1913 ‘ Henry Mosley ‘ made periodic table by the increasing order of atomic number and same physical and chemical properties . He also predict the ‘modern periodic law’
The modern periodic law states that ‘ properties of elements are a periodic function of their atomic number’
This periodic table is accepted.
➢ Arrangement of modern periodic table :
In modern periodic table elements arrange by their increasing of atomic number in the blocks
• In modern periodic table 18 vertical column (groups) and 7 horizontal rows (periods) are present.
In periods elements are arrange by the same number of valance electron present in shell.
In rows they are arrange by increasing order of atomic number.
• In modern periodic table 4 blocks are present 4 blocks are differentiated on the basic of their physical and chemical properties.
• 4 blocks : s, p , d, f
In s block 1 and 2 group elements are present.
1st group element is alkali metal and 2nd group element is alkaline earth metals.
All the elements in s block having the same physical and chemical properties
S block elements Have their outermost electron in s orbital.
P block :
In p block 13 to 18 group element is present.
Metal, Metalloids and Nobel gas are present in p block.
All the p block elements have their outermost electron in p orbital.
In d block 3- 12 group elements are present.
Metals are generally present in d blocks.
All the elements present in d blocks have their outermost electron occupy in d orbit.
In f block lanthanide and actinides series are present.
It is mainly radio active elements.
The lanthanide and actinides series place at the bottom of periodic table.
This is all about arrangement of periodic table.
Notation of element in periodic table :
At the top of left side year of discovery is written
At the bottom of left side name of element is written
At the middle. Atomic symbol is present
At the top of left hand side atomic number is written
And at the bottom of right hand side atomic mass is written .
Terms related to periodic table
1) Atomic number : the number of proton or number of electron present in atom is called as atomic number .
It is denote by Z
e.g. atomic number of carbon is 6 In carbon 6 number of proton or electron is present
2) Atomic mass (weight): the addition of number of proton and neutron present in the nucleus of element is called atomic mass
It is denoted by A
e.g. atomic mass of nitrogen is 14.066 gm/ mol -1
In nitrogen 7 proton and 7 neutron is present.
Addition of this is 14 . Hence nitrogen have 14 atomic weight .
3) Proton : proton is a positive charge particles present in nucleus of atom
It is denoted by P
4) Neutron : neutron is a charge less particles present in nucleus of atom
It is denoted by N
5) Electron : electron is a negative charge particle revolve around the nucleus in a orbital
It is denoted by e
6) Shell : K, L , M, N shell is present in atom
The capacity of K shell is 2 electrons
The capacity of L shell is 8 electrons
The capacity of M shell is 18 electrons
The capacity of N shell is 32 electrons
7) Atomic size : it is also known as atomic radius
Atomic size is the distance between the centre of the nucleus and the outer most shell of atom .
8) Valency : the number of valance electron present in outer most shell of atom .
Valency of sodium is 1 because it contain only 1 valence electron
9) Isotopes : isotopes is the element which having same atomic number but different atomic mass
e.g. hydrogen have 2 isotopes i.e. deuterium and tritium . Deuterium have atomic weight is 2 gm/mol -1 and tritium have atomic weight is 3 gm /mol -1