Ionization Energy of Sodium from Wavelength | JEE Main PYQ | Structure of Atom
Q. The ionization energy of sodium in kJ mol⁻¹, if electromagnetic radiation of wavelength 242 nm is just sufficient to ionize sodium atom is ______.

Correct Answer: 494 kJ mol⁻¹

Explanation

Energy of one photon:

E = hc / λ

E = (6.626 × 10⁻³⁴ × 3 × 10⁸) / (242 × 10⁻⁹)

E ≈ 8.21 × 10⁻¹⁹ J per atom

Ionization energy per mole:

E = 8.21 × 10⁻¹⁹ × 6.022 × 10²³

E ≈ 4.94 × 10⁵ J mol⁻¹ = 494 kJ mol⁻¹

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