Definition:
- Atoms with same atomic number (number of proton), but different atomic weight (number of protons and neutrons).
- Atoms of same element with different atomic weight.
Types of isotope:
- Stable isotope
- Stability of an isotope depends on the definite neutron to ration which is specific for a specific atom.
- In atoms of low atomic weight stability is usually achieved with neutron to proton ration around one.
- In atoms of high atomic stability is usually achieved with more neutron than proton
- Neutrally occurring isotopes of most of the predominant elements are stable isotopes.
- Unstable isotope
- These are the isotopes having neutron to proton ration far away from its stability ratio.
- Neutrally occurring isotopes of heavy elements are usually unstable
- Rarely some naturally occurring isotopes of lighter elements can also be unstable
- Unstable isotopes tend to become stable by radio active decay
