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# Electromagnetic radiation of wavelength 242 nm is just sufficient to ionise the sodium atom. Calculate the ionisation energy of sodium in kJ mol -1 .

2.10  Electromagnetic radiation of wavelength 242 nm is just sufficient to ionise the sodium atom. Calculate the ionisation energy of sodium in kJ mol–1.

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Given the wavelength of the electromagnetic radiation is $242\ nm$ which is just sufficient to ionize the sodium atom.

So, the ionization energy required will be:

$E = Nh\nu = N\frac{hc}{\lambda}$

$= \left ( 6.022\times10^{23} mol^{-1} \right )\left ( \frac{6.022\times10^{23}J.s\times 3.0\times10^8 ms^{-1}}{242\times10^{-9 } m} \right )$

$= 4.945\times10^5 Jmol^{-1} = 494.5 kJmol^{-1}$

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