1. Periodic properties of the elements
Chapter 8

2. Quantum numbers Principal quantum number, n
Determines size and overall energy of orbital
Positive integer 1, 2,
Corresponds to Bohr energy levels

3. Quantum numbers Angular momentum quantum number, l
Determines shape of orbital
Positive integer 0, 1, (n–1)
Corresponds to sublevels l
letter s 1 p 2 d 3 f

4. Quantum numbers Magnetic quantum number, ml
Determines number of orbitals in a sublevel and orientation of each orbital in xyz space
integers –l l

5. What type of orbital is designated by each set of quantum numbers?
n = 5, l = 1, ml = 0 5p
n = 4, l = 2, ml = –2 4d
n = 2, l = 0, ml = 0 2s
Write a set of quantum numbers for each orbital
4s n = 4, l = 0, ml = 0
3d n = 3, l = 2, ml = –2, –1, 0, +1, or +2
5p n = 5, l = 1, ml = –1, 0, or +1

6. Electron configurations
Electrons exist within orbitals, given by three quantum numbers n, l, and ml

7. Electron configurations
Configuration shows which orbitals are occupied
Aufbau principle: e– takes lowest available energy
Hund’s rule: if there are 2 or more orbitals of equal energy (degenerate orbitals), e– will occupy all orbitals singly before pairing

8. Electron configurations
Electron has spin, either “up” or “down”
Electron spin given by 4th quantum number, ms
Pauli exclusion principle: no two e– in an atom can have the same set of 4 quantum numbers ⇒ 2 e– per orbital, one up ↑ and one down ↓

10. Magnetic properties
Atom or ion with unpaired e– is attracted to a magnetic field = paramagnetic
Atom or ion with all e– paired is slightly repelled by a magnetic field = diamagnetic

11. Effective nuclear charge: Zeff
Electron experiences attraction of nucleus and repulsion of other e– in the atom
Outer e– is partially shielded from full charge of nucleus
Zeff = actual nuclear charge – charge shielded by other e–

12. Effective nuclear charge: Zeff
Core e– effectively shield outer e– from nuclear charge
Outer e– do not shield other outer e– very efficiently
Thus,
Li outer e– experiences Zeff ≈ 3–2 = +1
Be outer e– experience Zeff ≈ 4–2 = +2

13. Trends in atomic radius
Atomic radius increases down a group
Same Zeff
Outer e– in higher principal energy level = larger orbital
Atomic radius decreases across a period
Same principal energy level
Increasing Zeff pulls in outer e–

14. Trends in atomic radius
Transition metal radii stay roughly constant across a period
Outer e– stay same
Adding protons to nucleus and electrons to n–1 (core) orbital, so Zeff stays about constant

17. Ions and ionic radii Elements may lose or gain outer e– to form ions
Metals lose e– → cations
Nonmetals gain e– → anions
The ions in these examples are isoelectronic (same e– configuration)

18. Transition metal ions
Transition metals lose their ns e– before losing their (n–1)d e–

19. Ions and ionic radii
A cation is much smaller than its parent atom

20. Ions and ionic radii
An anion is much larger than its parent atom

21. Ions and ionic radii
For isoelectronic species, the one with the highest nuclear charge will have the smallest radius
S2–
18 electrons
16 protons
184 pm
Cl1–
17 protons
181 pm
K1+
19 protons
133 pm
Ca2+
20 protons
99 pm

22. Ionization energy
Ionization energy (IE) = energy needed to remove e– from atom/ion in gaseous state
IE always positive (endothermic)
Successive IE values always increase
IE increases dramatically when begin to remove core e–

23. Trends in 1st ionization energy
IE1 decreases down a group
Same Zeff
Outer e– in higher principal energy level = farther from nucleus, easier to remove
IE1 generally increases across a period
Increasing Zeff pulls outer e– closer to nucleus, harder to remove

25. Two important exceptions
1st e– in p sublevel
3s orbital penetrates closer to nucleus
3p e– somewhat more shielded from nuclear charge, easier to remove
e– begin pairing in p sublevel
P S

26. Electron affinity (EA)
EA = energy change when gaseous atom/ion gains an e–
Trends less regular but generally becomes more exothermic across a period

27. Summary of periodic trends
Across a period
atomic radius decreases
IE1 (always endothermic) increases (with two important exceptions)
EA generally becomes more exothermic
Down a group
atomic radius increases
IE1 decreases