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

Explanation

We know that
`E = hv `
`E = ( hc)/( lamda) ...(i) because v = (c )/(lamda)`
Given, ` lamda = 242 nm`
`lamda = 242 xx 10 ^(-9) m " " because 1 nm = 10 ^(-9) m`
`therefore E = (( 6. 626 xx 10 ^(-34) Js) ( 3. 0 xx 10 ^(8) ms ^(-1)))/( 242 xx 10 ^(-9) m ) because h = 6.626 xx 10 ^(-34) jp , C = 3. 0 xx 10 ^(8) ms ^(1)`
`E =8.21 xx 10 ^(-19) J`
Ionisation energy per mol `= 8.21 xx 0 ^(-9) J xx 6. 0 23 xx 10 ^(3) = 494 xx 10 ^(3)J = 494 kJ mol ^(-1).`