Define (i) mass number, (ii) relative atomic mass - Leaving Cert Chemistry - Question (b) - 2014

Relative atomic mass is the average mass of the atoms of an element, taking into account the abundances of the isotopes of that element, relative to 1/12 of the mass of a carbon-12 atom.

The two other fundamental processes that occur in mass spectrometry are ionisation to form positive ions and separation of ions.

1. Vaporisation
2. Ionisation
3. Acceleration
4. Separation
5. Detection

To calculate the relative atomic mass (RAM) of gallium:

1. Calculate the contributions from each isotope:

   • For gallium-69:

   $69 imes 60.1 = 4146.9$

   • For gallium-71:

   $71 imes 39.9 = 2839.9$

2. Sum the contributions:

   $4146.9 + 2839.9 = 6986.8$

3. Divide by 100 to find the average:

   $\text{Relative Atomic Mass} = \frac{6986.8}{100} = 69.868$

Thus, the relative atomic mass of gallium is approximately 69.9.