Download Answers to Critical Thinking Questions 4

Tutorial 4 – Answers to Critical Thinking Questions
The worksheets are available in the tutorials and form an integral part of the learning
outcomes and experience for this unit.
Model 1: Atomic Orbitals and Quantum Numbers
1.
2.
3.
4.
The angular momentum quantum number, l.
n
Possible l values
Orbital labels
1
0
s
2
0 and 1
s and p respectively
3
0, 1 and 2
s, p and d respectively
4
0, 1, 2 and 3
s, p, d and f respectively
l
Possible ml values
Orbital labels
0
0
1xs
1
1, 0, -1
3 × p {px, py, pz}
2
2, 1, 0, -1, -2
5×d
3
3, 2, 1, 0, -1, -2, -3
7×f
s orbitals have no planar nodes. p orbitals have one planar node. d orbitals have
two planar nodes.
5. The number of planar nodes is equal to the value of the angular momentum
quantum number, l.
6.
The 2s and 3pz orbitals both have one spherical node and 3dx2-y2 has none. In
general, the number of spherical nodes is equal to n – l - 1.
Model 2: Electronic Configurations in Atoms
7. a. The Aufbau principle: Orbitals are filled with electrons in order of energy with
the lowest energy orbital being filled first.
b. Pauli exclusion principle: no two electrons may have the same set of quantum
numbers. Each orbital can accommodate no more than 2 electrons. These 2
electrons will have opposite spin (ms).
c. Hund’s Rule: in a set of orbitals with the same energy, electrons may not be
spin-paired until each orbital in the set contains one electron.
8.
See figure.
a. The Pauli exclusion principle
means that a maximum of two
electrons can occupy an s orbital.
The electron configuration of
carbon 1s2 2s3 2p1 has three
electrons in 2s.
Hund’s rule means that the three
2p orbitals must each be occupied
before electrons can pair up.
b.
The configuration 1s2 2s2 2px2 has
two electrons spin-paired in 2px
with the 2py and 2pz empty.
9.
2
10. All s orbitals can only have a maximum of 2 electrons.
11. All p orbitals can only have a maximum of 6 electrons (= 3 x 2 for each degenerate
orbital).
12.
a) 1s22s22p63s23p44s1 – the 3p orbitals were not completely filled before electrons
were added to 4s (violating the Aufbau principle). The correct configuration is
1s22s22p63s23p5
b) 1s22s22p63s23p7 – the maximum number of electrons in 3p is 6 (violating the
Pauli exclusion principle). The correct configuration is 1s22s22p63s23p64s1
c) 1s22s22p63s23p63d2 – the 4s orbital has a lower energy than 3d, so it will be
filled first (violating the Aufbau principle). The correct configuration is
1s22s22p63s23p64s2
d) 1s22s22p63s23p64s23d104p65s23f 2 – there is no 3f orbital. The only orbitals with
a principal quantum number of 3 are s, p and d. The correct configuration is
1s22s22p63s23p64s23d104p65s24d 2
Model 3: Electronic Configurations in Atoms and Ions
13.
14. The 4s orbital comes before the 3d orbital. Because of electron shielding (which
results from the different shapes of the s and d orbitals), the 4s orbital has lower
energy than the 3d orbital.
15.
Atom
or ion
Number of Number of Electron configuration
protons
electrons
Cl
17
17
1s22s22p63s23p5
Noble gas configuration
(shorthand electron
configuration)
[Ne]3s23p5
Ar
18
18
1s22s22p63s23p6
[Ar]
K
19
19
1s22s22p63s23p64s1
[Ar]4s1
Ca
20
20
1s22s22p63s23p64s2
[Ar]4s2
Cl-
17
18
1s22s22p63s23p6
[Ar]
K+
19
18
1s22s22p63s23p6
[Ar]
Ca2+
20
18
1s22s22p63s23p6
2
6
2
6
[Ar]
Zn
30
30
1s 2s 2p 3s 3p 4s 3d
[Ar]4s23d10
Sr
38
38
1s22s22p63s23p64s23d104p65s2
[Kr]5s2
Sr2+
38
36
1s22s22p63s23p64s23d104p6
[Kr]
16. Ar, Cl-, K+, Ca2+
17. Kr, Rb+, Br-, Se218. Sr
19. K
20. Cl
21. Zn
2
2
10