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5.ATOMIC STRUCTURE eLearn.Punjab
(a) When the electron moves from n = 1 to n = 2, how much does the radius of the orbit
increases.
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(Ans: 1.587 A )
(b) What is the distance travelled by the electron when it goes from n=2 to n=3 and n=9
ton=10?
[e0 = 8.85x 10-12 c2J-1 m-1 , h = 6.624 x.10-34 js, p = 3.14, m = 9.108x 10-31 kg, e = 1.602 x 10-19c]
while doing calculations take care of units of energy parameter.
[J = kgm2 s-2, c = kg1/2 m3/2 s-1]
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(Ans: 2.65 A ; 10.05 A )
Q 20 Answer the following questions, by performing the calculations.
(a) Calculate the energy of first five orbits of hydrogen atom and determine the energy
differences between them.
(b) Justify that energy difference between second and third orbits is approximately five
times smaller than that between first and second orbits.
(c) Calculate the energy of electron in He+ in first five orbits and justify that the energy
differences are different from those of hydrogen atom.
(d) Do you think that groups of the spectral lines of He+ are at different places than those
for hydrogen atom? Give reasons.
Q 21 Calculate the value of principal quantum number if an electron in hydrogen atom revolves in
an orbit of energy- 0.242 xlO-18 J.
(Ans:n=3)
Q 22 Bohr’s formula for the energy levels of hydrogen atom for any system say H, He+,Li2+ ,etc. is
En = -Z2e4m
8e0 2h2n2
or
En = -K  Z2 
 n2 
 
For hydrogen:Z = 1 and for He+, Z = 2.
(a) Draw an energy level diagram for hydrogen atom and He+ .
(b) Thinking that K = 2.18 x 10-18J, calculate the energy needed to remove the electron from
hydrogen atom and from He+.
(Ans: 2.18 x 10-18J; 8.72x10-18J)
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