Exercises-Part 1 2020

Home exercises
Part 1
1. The wavelength of the green light from a traffic signal is centered at 522 nm. What is the
frequency of this radiation?
2. Calculate the energy (in joules) of
a) a photon with a wavelength of 5.00x104 nm (Infrared region)
b) a photon with a wavelength of 5.00x10-2 nm.
3. The energy of a photon is 5.87x10-20 J. What is the wavelength (in nanometers)?
4. What is the wavelength of a photon emitted during a transition from the n i=5 state to the nf = 2
in the hydrogen atom?
5. Calculate the wavelength in the following two cases:
* The wavelength of an electron traveling at 1.24x107 m/s. me = 9.1x10-31 kg
* The wavelength of a baseball of mass 149g traveling at 41.3m/s.
6. Calculate the wavelength of the “particle” in the following two cases:
a) The fastest serve in tennis is about 62 m/s. Calculate the wavelength associated with a
6.0x10-2 kg tennis ball traveling at this velocity
b) Calculate the wavelength associated with an electron moving at 62 m/s.
7. How many individual orbitals are there in the third shell? Write out n, l, m l quantum numbers
for each one and label each set by the s, p, d, f designations.
8. Describe the characteristics of an s orbital, a p orbital, and a d orbital. Which of the following
orbitals do not exist: 1p, 2s, 2d, 3p, 3d, 3f, 4g?
9. What is the maximum number of electrons in an atom that can have the following quantum
numbers? Specify the orbitals in which the electrons would be found. (a) n = 2, ms = +1/2;
(b) n=4, ml = +1; (c) n=3, l =2; (d) n=2, l=0, ms = +1/2; (e) n=4, l =3, ml =-2
10. An electron in a certain atom is in the n=2 quantum level. List the possible values of l and m l
that it can have.
11. List all the possible subshells and orbitals associated with the principle quantum number n, if
n=5.
12. Indicate which of the following sets of quantum numbers in an atom are unacceptable and
explain why:
(a) (1,0,1/2,1/2) (b) (3,0,0,+1/2) (c) (2,2,1,+1/2)
(d) (4,3,-2,+1/2) (e) (3,2,1,1,)
13. Indicate the number of unpaired electrons present in each of the following atoms: B (Z=5),
Ne (Z=10), P (Z=15), Sc (Z=21), Mn (Z=25), Se (Z=34), Kr (Z=36), Fe (Z=26), I (Z=53), Pb
(Z=82), Cd (Z=48).
d 2 2
Z2
14. Draw the shapes (boundary surfaces) of the following orbitals: a) 2py; b) 3 ; c) 3d x − y
15. Draw orbital diagrams for atoms with the following configuration:
a) 1s22s22p5 b) 1s22s22p63s23p3 c) 1s22s22p63s23p64s23d7
16. The ground-state electron configurations listed here are incorrect. Explain what mistakes
have been made in each and write the correct electron configurations
Al: 1s22s22p43s23p3
B: 1s22s22p5
F: 1s22s22p6
17. Without referring to a periodic table, write the electron configuration of the elements with
the following atomic numbers: a) 9; b) 20; c) 26; d) 33. Classify the elements.
18. Specify the group of the periodic table in which each of the following elements is found: a)
[Ne] 3s1, b) [Ne]3s23p3, c) [Ne]3s23p6, d) [Ar]4s23d8
19. A M2+ ion derived from a metal in the 1 st transition metal series has four electrons in the 3d
subshell. What element might M be?
20. In general, ionization energy increases from left to right across a given period. Aluminum,
however, has lower ionization energy than magnesium. Explain.
Al has one unpaired electron in its highest energy orbital (3p), and Mg's highest energy
orbital (3s) has the paired electrons. It is energetically favorable for all the electrons in an
orbital to be paired, which means that breaking up this pair would require more energy.
21. Two atoms has the electron configurations 1s 22s22p6 and 1s22s22p63s1. The first ionization
energy of one is 2080 KJ/mol, and that of the other is 496 KJ/mol. Match each ionization
energy with one of the given electron configurations. Justify your choice.
22. A hydrogen-like ion is an ion containing only one electron. The energies of the electron in a
hydrogen-like ion are given by
( ) 1
En =−(2. 18 x 10−18 J )Z 2 2
n
Where n is the principle quantum number and Z is the atomic number of the element.
Calculate the ionization energy of the He+ ion.
23. From the following data, calculate the average bond energy for the N-H bond:
NH3(g) ® NH2(g) + H(g) DHo = 435KJ
NH2(g) ® NH(g) + H(g) DHo = 381 KJ
NH(g) ® N(g) + H(g) DHo = 360 KJ
24. The energy needed for the following process is 1.96x104KJ.mol-1:
Li(g) ® Li3+ (g) + 3e-
If the first ionization energy for lithium is 520 kJ/mol -1, calculate the second ionization
energy of lithium, that is, the energy required for the process
Li+(g) ® Li2+(g) + e-
(Use the equation:

( )n
1
En =−(2. 18 x 10−18 J )Z 2 2
)
25. According to VB theory, explain, why the nitrogen atom cannot have pentavalence, while the
phosphorus has.
26. Determine and explain all possible valences of the following atoms: S, Cl, C.
27. Draw a Lewis formula for the following species: H2O, H3O+, NF3, OF2, BF3, [BF4]-, SF4, SF6.
28. What is the hybridization of the central atom in each of the following: NCl 3, CF4, SF6, NH3,
NH4+.
29. What hybridizations are predicted for the central atoms in the following molecules:
H2O H2S H2Se H2Te
104.5 o
92.2 o
91o 89.5o
Why the bond angles decrease by the above order?
30. Predict geometry of the following molecules: H2O, H3O+, CH4, CO2, SO2, BF3.
31. Describe the hybridization of N in each of these species:
i) NH3; ii) NH4+; iii) H N̈ = N̈ H; iv) ; v) H2 N̈ - N̈ H2
32. What change in hybridization occurs in the following reaction?
:NH3 + BF3 →H3N: BF3
31. Briefly discuss the bond angles in the hydroxylamine molecule in terms of the ideal geometry
and the small changes caused by electron-pair repulsions.
32. Use the appropriate molecular orbital energy diagram to write the electron configuration for
each of the following; calculate the bond order of each, and predict which would exist (a)
H2+; (b) H2; (c) H2-; (d) H22-.
33. Repeat exercise 32 for (a) He2+; (b) He2; (c) He22+
34. Repeat exercise 32 for (a) N2; (b) Ne2; (c)C22-
35. Repeat exercise 32 for (a) Li2; (b) Li2+; (c) O22-
36. Use the appropriate molecular orbital energy diagram to write electron configurations of the
following molecules and ions: (a) Be2, Be2+, Be2-; (b) B2, B2+, B2-.
37. Use the preceding diagram to fill in an MO diagram for NO -, what is the bond order of NO - ?
It is paramagnetic? How would you assess its stability?
38. Repeat exercise 37 for NO+
39. Repeat exercise 37 for CN +. Refer to the preceding diagram but assume that the P2px P2py
MOs are lower in energy than the 2σp MO.
40. Explain why ionization energies of molecules H2, N2, C2, CO higher than those of the
corresponding atoms ?
H C N O F
I1 (KJ.mol )-1
1308 1083 1396 1312 1675
H2 C2 N2 O2 F2
I1 (KJ.mol )-1
1488 1154 1507 1173 1526
41. Compare dipole moment of the following molecules: NH3 and NF3 and explain?
42. Do the following molecules have dipole moment ? Explain?
F2; BeF2; BF3; CF4; CO2; SO2

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