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

Energy possessed by electronmagnetic radiation with wavelength 242 nm will be equal to ionization energy,
`E = hv = (hc)/(lambda)`
`h = 6.626 xx 10^(34) Js`
`c = 3.0 xx 10^(8) m, lambda = 242 xx 10^(-9)m`
`:. E = ((6.626 xx 10^(-34) Js) xx (3.0 xx 10^8 ms^(-1)))/((242 xx 10^(-9)m))`
`= 8.21 xx 10^(-19) J`
Ionization energy per mol = `8.21 xx 10^(-19) J xx 6.023 xx 10^(23)`
`=494 xx 10^3 J = 494 kJ mol^(-1)`.