AP Chemistry: Class 33

Period E – Monday, November 4th

Chapter 7 Terms

• valence orbitals
• effective nuclear charge
• atomic radius
• isoelectronic
• ionization energy
• electron affinity
• metallic character

Class Activity – Trends

• Take a look at the shared spreadsheet [LINK]
• Note: Google Drive – Lecture & Content – Atomic Property Information
• Open the “Numbers” app on your iPad
• Create a graph for each of the columns
  • Z vs IE
  • Z vs AR
  • Z vs IR
• Be sure and label properly and scale each accordingly
• Write an explanation for each graph that correlates to the elements
• NOTE: use as many of the terms from the list above as are appropriate
• SUBMIT: turn in as a PDF to Dropbox folder, including proper graphs and commentary

Homework

• Ch. 7 (16, 25, 28, 37, 45, 47, 93) on paper
• Finish the graphing assignment

Answer

• the key to the trends is understanding effective nuclear charge
• Zeff is the “net protons” that can “see through” the full levels in an atom
• Example
  • Na = 11 protons, 2 full shells (10 electrons) Zeff = 11-10 = 1
  • Mg = 12 protons, 2 full shells (10 electrons) Zeff = 12-10 = 2
  • Atomic radius of Mg < Na because greater pull on outer electrons
  • Ionization energy Mg > Na because greater pull on outer electrons
• Once there is an electron in a shell then adding more does not increase size – level already exists (analogy = floors in a building: once the floor is built then adding more people doesn’t change overall height of building)
• Adding a level DOES change average electron distance
  • atomic radius Na > Li (3 levels vs 2 levels with same Zeff)
  • ionization energy Li > Na because electrons close in Li, harder to remove
• Ion sizes (and ionization energies) are largely determined by the RATIO of protons to electrons
  • size of Mg+2 < Na+1 because Mg has 12 protons and Na has 11 protons (both have 10 electrons)