Isotopes

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Isotopes

Isotopes: Atoms of the same element that contain different numbers of neutrons

Mass number: The number of protons and neutrons in one atom of an element. The mass number is always a whole number.

Relative atomic mass: The weighted mean mass of an atom of an element compared to \( \frac{1}{12} \) of the mass of an atom of carbon-12.

Relative atomic mass = \( \frac{\text{Total mass of the atoms}}{\text{Total number of atoms}} \)

Relative formula mass: The sum of the relative atomic masses of all the atoms in the empirical formula of an molecule

Relative molecular mass: The sum of the relative atomic masses of all the atoms in a molecule

Relative isotopic mass: The mass of an individual atom of a particular isotope relative to \( \frac{1}{12} \) of the mass of an atom of carbon-12. This is not likely to be a whole number.

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Example Calculation:

The abundances of the two isotopes of Cl are 75% and 25% of Cl-35 and Cl-37 respectively.

If we take 100 atoms, the relative atomic mass is = \[ \frac{\text{Total mass of the atoms}}{\text{Total number of atoms}} \ \] \[ \frac{\text{(75x35) + (25x37)}}{\text{100}} \ = 35.5\]

The relative atomic mass of chlorine is 35.5