Question

Question 2.10 Electromagnetic radiation of wavelength 242 nm is just sufficient to ionise the sodium atom. Calculate the ionisation energy of sodium in kJ mol–1.

Class XI Structure of Atom Page 65

Answer 1

Here,
wavelength ( λ ) = 242 nm = 2.42 × 10^-7 m
we know,
Energy ( E ) = hc/λ
here, h is Plank's constant
c is the speed of light
and λ is the wavelength of photons
so, E = 6.626 × 10^-34 Js × 3 × 10^8 m/s /2.42 × 10^-7 m
= 0.0821 × 10^-17 J / atom

0.0821 × 10^-17 J energy is sufficient for ionisation of one Na atom , so it is the ionisation energy of Na .
hence, I.E = 0.0821 × 10^-17 J/atom
= 0.0821 × 10^-17 × 6.022 × 10²² J/mol
= 4.945 × 10^5 J/mol
= 4.945 × 10² KJ/mol

Answer 2

Answer:2.10

Explanation:HERE WAVELENGTH=242nm

SO IT CAN BE WRITTEN AS = 242×10^-9m