Wednesday, 17 June 2015

Atomic Number, Mass Number, Isotopes and Isobars

Atomic Number

Number of protons present in nucleus of atom of an element is known as atomic number.
It is denoted by (z)
example : Carbon have 6 protons so its atomic number is 6 (z = 6)
For neutral atom,
 atomic number (z) = number of protons (p) = number of electron (e)
Number of protons in cation > Number of electrons in cation
Number of protons in anion < Number of electrons in anion
Number of protons in neutral atom = Number of electron in neutral atom

Mass Number

Mass number is also known as atomic mass. Atomic number or mass number is equal to number of protons and neutrons in atom.
Atomic mass = number of protons + number of neutrons
                 A = p+n
example : Helium have two protons and two neutrons so its atomic mass is 2+2=4


Atoms of same elements which have same atomic number but different mass number is called isotopes.
example : Protium, Deutrium, Tritium are isotopes of hydrogen.

Types of Isotopes

1. Non-radioactive isotope 

                       Example C(12), C(13)

2. Radioactive isotopes 

                       Example U(235), U(233), U(238), U(239)


Atoms of different elements which have similar atomic mass and different atomic number are called isobars.
example : Ca(40), Ar(40), Kr(40)
                 50Cr24, 50Ti22
Isobars do not similar in physical and chemical properties

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