An Electromagnetic radiation of wavelength `242` nm is just sufficient to ionise a sodium atom .Calculate the ionisation energy of sodium in `KJ mol^(-1)`.

Explanation

The energy required to ionise one atom is given by `E= (hc)/(lamda) {{:(h= 6.626 xx 10^(-34)J.s),(c=3 xx 10^(8) ms^(-1)),(lamda= 242 xx 10^(-9) "metre"):}}`
Thus the energy required to ionise one mole (i.e., Av. Const) of Na atoms is `E= ((6.626 xx 10^(-34)) (3 xx 10^(8)))/(242 xx 10^(-9)) xx 6.022 xx 10^(23)`
`=4.946 xx 10^(5)J "mole"^(-1)`
`=4.946 xx 10^(2)kJ "mole"^(-1)`