1. yChemistry is explained through sharing or transferring electrons. yThis determines which elements can bond and what type of bond they form Why is this VERY important? Electron Configurations and Periodicity.

2. yWhat is an electron configuration? How are the electrons arranged in an atom? What orbitals are preferentially filled by electrons?

3. C. Johannesson yEnergy levels (refer to periods on periodic table) yAlso referred to as “shells” y7energy levels 1, 2, 3, 4 …7 yEnergy level 1 is lowest in energy and closest to the nucleus Energy levels and sublevels

4. C. Johannesson Sub-levels yThe main energy levels contain sub-levels (refer to groups on periodic table #1-18) yThe different main energy levels have different sub-levels in them yThere are four types based on shape of orbitals: s (groups 1-2) lowest energy, p, (13-18) d (transition metals), f (inner transition metals) highest energy

5. C. Johannesson Electron Configuration Electrons in Atoms

6. Hints for rules z1) The Pauli Exclusion Principle (not allowed) z2) The Aufbau Principle (building up or Lazy tenant rule) z3) Hund’s Rule (empty bus seat rule) C. Johannesson 3 RULES FOR THE ARRANGEMENT OF ELECTRONS IN ATOMS.

7. A. General Rules zPauli Exclusion Principle yEach orbital can only hold TWO electrons with opposite spins. yNo 2 electrons in the same atom can have the same set of all 4 quantum numbers (electrons can not occupy same space nor have the same spin) Right Wrong

8. C. Johannesson General Rules: Aufbau Principle yElectrons fill the lowest energy orbitals first. y(means building-up in German) in the ground state, the electrons will fill the atomic orbital of lowest energy first; “Lazy Tenant Rule”

9. C. Johannesson RIGHT WRONG A. General Rules zHund’s Rule yWithin a sublevel, place one electron per orbital before pairing them. y“Empty Bus Seat Rule”

10. C. Johannesson O 8e - zOrbital Diagram zElectron Configuration 1s 2 2s 2 2p 4 B. Notation 1s 2s 2p

11. C. Johannesson S 16e - Valence Electrons Core Electrons 1s 2 2s 2 2p 6 3s 2 3p 4 B. Notation zLonghand Configuration Outermost electrons in highest enrgy level

12. C. Johannesson © 1998 by Harcourt Brace & Company s p d (n-1) f (n-2) 12345671234567 6767 C. Periodic Patterns

13. C. Johannesson C. Periodic Patterns zPeriod # yenergy level (subtract for d & f) zGroup # ytotal # of valence e - zColumn within sublevel block y# of e - in sublevel

14. C. Johannesson s-block1st Period 1s 1 1st column of s-block C. Periodic Patterns zExample - Hydrogen