Electromagnetic radiation of wavelength 242 nm is just sufficient to ionise the sodium atom. What is the ionisation energy of sodium per atom?

Explanation

lonisation energy of sodium per atom = Energy of the radiation used hc
`=(hc)/(lambda)=(6.626 xx 10^(-34) xx 3 xx 10^(8))/(242 xx 10^(-9))`
`=8.214 xx 10^(-19) " J atom"^(-1) (lambda=242nm=242 xx 10^(-9)m)`
Ionisation energy of sodium per mole
`=8.214 xx 10^(-19)xx 6.022 xx 10^(23)`
`=4.946 xx 10^(5) " J mol"^(-1)`
`=494.6"kJ mol"^(-1)`