<span>First divide the ionization energy by Avogadro's number to get the energy per atom of potassium; </span>419 kj/mol / 6.023 x 10²³ = 4.19 x 10⁵ / 6.023 x 10²³ = 6.96 x 10⁻¹⁹ E = hc/λ where lambda (λ<span>) is the wavelength, h is Planck's constant, c is the speed of light </span>E = 6.96 x 10⁻¹⁹ j/atom<span> h =</span>6.63x10⁻³⁴<span> Js c = 3 x 10</span>⁸ m/s λ = ? λ = hc/E = (6.63x10⁻³⁴ x 3 x 10⁸ ) / 6.96 x 10⁻¹⁹ = 285.8nm = 286nm <span>The longest wavelength of light capable of this ionization is 286nm.</span>
