Question

Electromagnetic radiation of wavelength 242 nm is just sufficient to ionize sodium atom. Calculate the ionization energy of sodium atom. $\left(c=3 \times 10^{8} ms ^{-1}, h \right.$ $=6.626 \times 10^{-34}$ J.S).

Answer 1

Radiation of wavelength $242 nm$ removes the electron from sodium atom to produce sodium ion. Hence the energy corresponding to the wavelength is the ionization energy.

We know that $E=h v=\frac{h \times c}{\lambda}$

$\therefore \quad E=\frac{-6.626 \times 10^{-34} J.s \times 3 \times 10^{8} ms ^{-1}}{242 \times 10^{-9} m }$ per atom

$=\frac{6 \cdot 626 \times 3}{.242} \times 10^{-17} J$ per atom

$= 8 \cdot 21 \times 10^{-19} J$ per atom.