1. Chapter 5.4 – Atomic Energies and Periodicity
CHM1111 Section 04
Instructor: Dr. Jules Carlson
Class Time: M/W/F 1:30-2:20
Friday, October 14th

2. Atomic Properties
Going to look at 5 properties and trends in these properties for elements with periodic table.
Orbital size and stability
Size of Atomic Radii (neutral)
Ionization Energy
Electron Affinity
Size of Atomic Ions

3. Electron Affinity
Atomic number (Z) can be used to describe trends in orbital size and stability.

4. Atomic Radii
Most of the volume of an atom is occupied by it’s electron cloud, so electron orbital sizes control atomic radii size.
Atomic Radii increase
Little difference across transition metals due to screening.
Atomic Radii decrease

5. Atomic Radii Trends
Fast decrease in atomic radii size across s and p blocks
Slower decrease in atomic radii along d and f blocks
Effect of larger atomic radius with higher n is smaller than effect of size decreases across a row.

6. Atomic Radii Problem
Which compound has a larger atomic radii out of the following pairs:
Mg or Cl
Li or Rb
Na or I

7. Ionization Energy
The minimum amount of energy needed to remove an electron from a neutral atom is the First Ionization Energy, IE1.
Ionization energy decreases
Little difference across transition metals due to screening.
Ionization Energy increases

8. Ionization Energy Trend Reasoning
As n increases, the orbital energies get closer together, so IE decreases.
As you go from left to right, the charge on the nucleus increases making ground state orbitals more stable, so IE increases.

9. Ionization Energy Trends
IE1 decreases with increasing n (small effect)
IE1 increases with increasing electron orbital filling within a period (large effect)

10. Irregularities in Ionization Energies
Some exception occur in ionization energy trends due to screening effects.
Element Z
Atom Configuration
IE1
Cation Configuration Mg 12
[Ne] 3s2
738 kJ/mol
[Ne] 3s1 Al 13
[Ne] 3s2 3p1
577 kJ/mol Si 14
[Ne] 3s2 3p2
786 kJ/mol
Element Z
Atom Configuration
IE1
Cation Configuration N 7
1s2 2s2 2p3
1402 kJ/mol
1s2 2s2 2p2 O 8
1s2 2s2 2p4
1314 kJ/mol F 9
1s2 2s2 2p5
1681 kJ/mol

11. Higher Ionizations
Removing successive electrons takes more and more energy.
Also, removing core electrons requires far more energy than removing valence electrons.
Process
Configurations IE
Mg (g) → Mg+ (g) + e−
[Ne]3s2   →
[Ne]3s1
739 kJ/mol
Mg+ (g) → Mg2+ (g) + e−
[Ne]3s1   →
[Ne]
1450 kJ/mol
Mg2+ (g) → Mg3+ (g) + e−
[Ne]   →
[He]2s22p5
7730 kJ/mol
IE1
IE2
IE3

12. Ionization Energy Problem
Which compound has a larger ionization energy out of the following pairs:
Mg or Cl
Li or Rb
Na or I
Mg+ or Mg
Na+ or Mg+

13. First 3 Properties – Arrows increasing
Orbital stability
Orbital size
Atomic Radii
Ionization Energy
Little effect - screening
Little effect - screening

14. I Clicker Question
Consider the following table, which of the following will have the largest value of each property?
A, B, B, C
B, A, B, B
B, A, B, C
A, A, C, C
C, A, C, C
Property A B C
Orbital Stability Li F Cs
Atomic Radii Na Cl I
Ionization Energy Rb Ca
Ca+ K+

15. Electron Affinity
Electron Affinity (EA): The energy released when an atom gains an electron.
F + e-  F- EA = -322 kJ/mol
No clear trend across transition metals
No clear trend with increasing n
Electron Affinity Increases

16. Electron Affinity Trends
Electron affinity increases along a row, especially for s, p blocks.
No clear trend as n increases.

17. Ion Size Cations are always smaller than corresponding neutral atoms
Anions are always larger than corresponding neutral atoms

18. Ions and Chemical Periodicity
Elements in s, d, f blocks form atomic cations, act as metals.
Most elements in p block form atomic anions, vary in behaviour from metals to metalloids to non-metals, to relatively inert atoms.
Elements in s block can ns1 or ns2 configurations.
Elements in d block have one or two ns electrons and various numbers of (n-1)d electrons.
Elements in the f block have two ns electrons and various numbers of (n-2)f electrons.

20. s-block Elements Alkali metals – Group 1, ns1 configuration
Alkaline earth metals – Group 2, ns2 configuration
Common in Earth’s crust, important to body function – Na, K, Ca, Mg
Key industrial products from s block elements – calcium oxide (lime), sodium hydroxide, and sodium carbonate

21. p-block Elements
Properties of elements in the p-block vary more than in the s block.
Al, Ga, In, Sn, Tl, Pb, Bi have metallic propeties and form cations.
Al, Ga, In form 3+ cations Al(OH)3 and GaF3.
Can form anions if strongly electronegative (group 7 halogens and oxygen).
Those less electronegative can form polyatomic oxoanions (eg. CO32- and NO3-), and halogens can too (eg. ClO4-).
Group 8 atoms are noble gases and were believed to be inert. It has been found that Xe, Kr can react with halogens (eg. XeF6).