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Homework 6
1.) A Hydrogen electron makes a transition from n=2 to n=4. Calculate the energy, frequency, and
wavelength of the photon. Do NOT use calculated values to calculate other values unless you
have NO choice. In what region of the spectrum is this photon?
 1
1 
-2.179 x 10-18 J  2  2 
 nH nL 
E=
 1
1 
E = -2.179 x 10-18 J  2  2  = 2.179 x 10-18 J (0.1875) = 4.086 x 10-19 J
4
2 

E = 4.086 x 10-19 J - since the electron goes from a lower n to a higher n, E
will be positive
 1
1
1 
 1.0968 x 10 7 m -1  2  2 

 n1 n2 
 1
1 
 1.0968 x 10 7 m -1  2  2  = 1.0968 x 107m-1 (0.1875)
4

2 

1
1
 2.056500 x 106 m-1


1
=
2.056500 x 10 6 m 1
4.8626 x 10-7 m - this is in the visible region (486.26
nm)
c = 
 = c/ = 2.9979 x 108m/s / 4.8626 x 10-7 m = 6.1652
x 1014 sec-1
Or
E = h
 = E/h = 4.086 x 10-19 J/6.626 x 10-34 Jsec = 6.167
x 1014 sec-1
2.) Which of the following quantum number sets are allowed? If there is an error identify AND
correct it with a valid quantum number – each incorrect set, only contains ONE error, therefore
only change ONE of the quantum numbers to make the set valid. If the set is valid, write the word
valid or ok after it!
a. n= 2, l= 1, ml= 0: valid
b. n= 2, l= 2, ml = 2: not valid – l and n cannot be the same number n = 3 (or greater)
c. n= 6, l= 4, ml= -5: not valid, ml cannot be outside –l . . .+ l therefore l = 5 ok or ml
betweent -4 . . . +4
d. n=6,
l=5, ml = -4: valid
3.) Write the electron configurations for
a. Zn: 1s22s22p63s23p64s23d10
b. Cu: 1s22s22p63s23p64s23d9 BUT!! Becomes 4s13d10
c. Cr: 1s22s22p63s23p64s23d4 BUT!! Becomes 4s13d5
d. Na: 1s22s22p63s1