What are the requirements for two atoms to be isotopes of each other?

The basic requirements for atoms to be an isotope is that:

1. They must have the same atomic number (i.e proton)

2. They must have different mass number.

Isotopy is a phenomenon where by two or more atoms have the same atomic number (i.e proton) but different mass number due to the difference in the neutron number of the atoms involved. The atoms involved in Isotopy are called isotopes.

Chlorine for example has 2 isotopes ³⁵₁₇Cl and ³⁷₁₇Cl.

Considering the two isotopes given above, we can see clearly that the two isotopes both have the same atomic number (i.e proton) but different mass number.

NOTE: The difference in mass number is due to the difference in the neutron number of the atoms.

Therefore, the basic requirement for atoms to be called isotope is that:

1. They must posses the same atomic number (i.e proton)

2. They must have different mass number. This is due to the difference in the neutron number of the atoms.

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