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Isotopes and Isobars

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Isotopes and Isobars - Lesson Summary

Symbolic representation of an atom

Z = Total number of protons present in an atom.
A = Total number of protons and neutrons present in an atom.

The atoms have the same atomic number but different mass numbers are called isotopes.

Isotopes of the same element occupy the same place in the periodic table because they have the same atomic number.

Ex: Isotopes of Hydrogen

Protium - ₁H¹ with one proton and zero neutrons.

Deuterium - ₁H² with one proton and one neutron.

Tritium - ₁H³ with one proton and two neutrons.

Isotopes of Carbon:

₆C-12 and ₆C-13

Isotopes of Chlorine:

₁₇Cl - 35 and ₁₇Cl - 37

The chemical properties of an element depend on the number of electrons present and their configuration within an atom and not on the number of neutrons, as the isotopes have the same number of electrons; they exhibit similar chemical properties but differ in physical properties because of difference in mass number.


Atoms of different elements with different atomic numbers but the same mass numbers are called isobars.

Isobars have different chemical properties because they have different atomic numbers.


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