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

Explanation

`E = N hv = Nh (c)/(lamda) = ((6.02 xx 10^(23) mol^(-1)) xx (6.626 xx 10^(-34) Js) xx (3 xx 10^(8) ms^(-1)))/(242 xx 10^(-9) m)`
`= 4.945 xx 10^(5) J mol^(-1) = 494.5 kJ mol^(-1)`