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Atomic number, Mass number and Atomic species

 Atomic number, Mass number and Atomic species

Atomic number or Nuclear charge 

(i) The number of protons present in the nucleus of the atom is called atomic number (Z). 
(ii) It was determined by Moseley as, 

V1/2 =a(z-b)

Where, v=X -  ray’s frequency

 Z= atomic number of the metal a & b are constant. 
(iii) Atomic number = Number of positive charge on nucleus = Number of protons in nucleus = Number of electrons in nutral atom.
 (iv) Two different elements can never have identical atomic number.

 Mass number 

Mass number (A) = Number of protons or Atomic number (Z) + Number of neutrons or Number of neutrons = A – Z .
 (i) Since mass of a proton or a neutron is not a whole number (on atomic weight scale), weight is not necessarily a whole number.
 (ii) The atom of an element X having mass number (A) and atomic number (Z) may be represented by a symbol, ZXA

Different types of atomic species

Isotopes

Given by Soddy

1.They are the atoms of a given element  which have the same Atomic number (Z) but different Mass number (A).

2.They have same number of protons and same number of electrons but  different number of neutrons.

3. They have same electronic confriguration , same chemical properties and same position in the periodic table but different physical properties. 

examples: 


 Isobars

Given by Aston 
1.They are the atoms of different elements which have the same Mass number (A) but different Atomic number(Z).
2.They have different number of electron , protons and neutrons but sum of number of protons and neutrons i.e. number of neucleons remains same .
3. They have different electronic configuration , chemical properties and the position in the periodic table. 
examples 

 Isotones

1.They are the atoms of different elements which have the same number of neutrons but different atomic number, mass number , number of protons and number of electrons.

2. They have the different electronic configuration, physical properties , chemical properties and position in the periodic table. 

examples 

Isodiaphers 

They are the atoms of different elements which have the same difference of the number of Neutrons and protons. 
examples 

Isoelectronic species 

They are the atoms of given element which have the same number of electrons and electronic configuration but different atomic numbet and mass number. 
examples 

Isosters 

they are the molecules which have the same number of atoms , number of electrons and physical properties and chemical properties. 
examples 



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