Question

The ionisation enthalpy of magnesium atoms is 737KJ/mol. Radiation of which frequency is required to remove an electron from the atom.

Answer 1

Hint: The ionisation enthalpy is defined as the energy which is required to remove the electron from the outermost orbital. The ionisation enthalpy depends on the penetration effect, the shielding effect and the electronic effect. The penetration effect is the proximity of the electron in the orbital to the nucleus.

Complete step by step answer:
Let us understand the terms in the question first.
A quantum of light is called a photon. Photons are minute energy packets of electromagnetic waves which are also called light quantum.
Wavelength is known as the distance between two successive crests or troughs of a wave. Wavelength is inversely proportional to frequency.
The frequency is the number of waves that pass a certain point in a specified amount of time.
The energy of the equation can be written as E = hν.
Energy of 1 mol = 7.38$ \times {10^2}$ KJ/mol
= 7.38$ \times {10^5}$ J/mol
Find energy of 1 photon first
Energy of 1 photon = $\dfrac{\text{energy of 1 mol}}{\text{Avogadro's number}}$
\[
   = \dfrac{{{\text{ }}7.38 \times {{10}^5}}}{{6.022 \times {{10}^{23}}}} \\
   = 1.226 \times {10^{ - 18}} J
 \]
This is the energy of 1 photon
E = hv
\[
  1.226 \times {10^{ - 18}} = 6.6 \times {10^{ - 34}}v \\
  v = 1.85 \times {10^{14}}Hz
 \]

Additional information:
Let us understand the relation between wavelength and frequency.
Wavelength is inversely proportional to frequency. So according to this longer wavelength, lower the frequency. So we can also say that shorter the wavelength, higher will be the frequency.
As we know that the wavelength and frequency are related to light, we can also relate them to energy. The shorter the wavelengths, the higher the frequency and it indicates greater energy. So the longer the wavelengths and lower the frequency results in lower energy.

Note: The ionisation energy increases from left to right in the period as the size of the atom decreases so the attractive force between the electron and the nucleus increases thereby increasing the ionisation enthalpy. The ionisation enthalpy decreases down the group. This is due to increases in the shells down the group so the atom size increases and the electron and nucleus attraction decreases.