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

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

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

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

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.

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

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

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.

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

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

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

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+

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

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+

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

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

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

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.

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

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).