Question

The colour of halogens progressively deepens from fluorine to iodine because:

• A. halogens of higher atomic number absorb light of longer wavelength since the difference in energy between the ground state and excited state decreases as the atomic number increases
• B. fluorescence and phosphorescence become more intense as the atomic numbers of halogen increases
• C. the standard electrode potential increases from $I_{2}to{F}_2$
• D. halogens of higher atomic number absorb light of shorter wavelength since the difference in energy between the ground state and excited state increases as the atomic number increases

Answer 1

Answer: (A)

Halogens of higher atomic number absorb light of longer wavelength since the difference in energy between the ground state and excited state decreases as the atomic number increases. Energy difference = $-13.6\times \frac{Z^2}{N^2}\times \frac{1}{n_1^2-n_2^2}$ For higher states, the energy difference is less. And, since, $E=\frac{hc}{\lambda }$, lesser energy implies higher wavelength.