Question

According to Bohr's theory, the electronic energy of hydrogen atom in the nth Bohr's orbit is given by
En= -21.76×10⁻¹⁹/n² J
Calculate the longest wavelength of light that would be needed to remove an electron from the third orbit of He⁺ ion.

Answer 1

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Answer 2

En of H = -21.76 *10-19/n2 J

∴ En of He+ = -21.76 *10-19/n2 * Z2 J

∴ E3 of He+ = -21.76 *10-19 *4/9 J

Hence energy equivalent to E3 must be supplied to remove the electron from 3rd orbit of He+. Wavelength corresponding to this energy can be determined by applying the relation.

E = hc/λ

or

λ = hc/E

= 6.625 *10-34 *3 */ 108 *9/21.76 *10-19 *4

= 2055 *10-10 m

= 2055 Å