How do you calculate the wavelength of light (in nm) required for mercury to emit an electron?
1 Answer
You must look up the ionization energy for mercury and use Planck's relation
The result will be
Explanation:
Since atoms can only absorb energy in discrete quantities, called photons, the energy of a single photon must be sufficient to provide the ionization energy of the atom. If not, the electron will jump into a higher bound state (a higher energy orbital) but will soon return to the ground state, with emission of a photon.
So, we require the ionization energy of mercury to do this calculation. You look this up - it is 1007 kJ/mol.
So, the minimum energy of a photon that will be able to remove an electron from mercury is this same value, 1007 kJ/mol.
We place this into Planck's relation for the energy and wavelength of absorbed photons
Since the units on ionization energy are kJ per mol, we must convert Planck's constant into a kJ s per mol value.