Question 1102042
What is the wavelength and frequency of light required to ionize a hydrogen atom (that is, to completely remove its electron)? This light is in what part of the EM spectrum?
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The ionization energy of hydrogen is 1312 kJ/mol. The energy required to ionize a single hydrogen atom is this quantity divided by Avagadro's number (the number of particles in a mole): 

(1.312*10^6 J/mol)/(6.022*10^23 atoms/mol) = 
2.179*10^-18 J/atom 


The energy of a photon is related to its wavelength by: 

E = h*c/wavelength 

where c is the speed of light in a vacuum = 2.998*10^8 m/s 
h is Planck's constant = 6.626*10^-34 (kg*m^2)/s 

Solving for the wavelength of a photon that has enough energy to ionize hydrogen: 

wavelength = (2.998*10^8 m/s)*(6.626*10^-34 (kg*m^2)/s)/(2.179*10^-18 J) 

wavelength = 9.118*10^-8 m = 91.18 nm