Question

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)`.

Answer 1

`lamda=242nm=242xx10^(-9)m`
`c=3xx10^(8)ms^(-1)`
`E=hv=h.(c)/(lamda)=6.6256xx10^(-34)xx(3xx10^(8))/(242xx10^(-9))`
`=0.082xx10^(-17)J=0.082xx10^(-20)kJ`
Energy per mole for ionisation `=0.082xx10^(-20)xx6.02xx10^(23)`
`=493.6kJmol^(-1)`.