Honors Chemistry Section 4.3 Electron Configurations Electron Configuration is the arrangement of electrons in an atom Every atom has a unique electron configuration Atoms tend to lowest E state, so normally exist in ground state Electron Configuration Aufbau Principle – Electrons occupy the lowest energy orbital available to them Pauli Exclusion Principle – No two electrons can have the same 4 quantum numbers Hund’s Rule – Orbitals of equal energy (called degenerate orbitals) are each occupied by one electron, before any is occupied by a second electron. All single electrons have the same spin. Rules for Electron Configuration Orbital Energies Hydrogen ◦ Helium ◦ ↿ 1s ↿⇂ 1s Oxygen ◦ ↿⇂ 1s ↿⇂ 2s ↿⇂ ↿⇂ ↿⇂ 2px 2py 2pz Orbital Notation Hydrogen ◦ 1s1 Helium ◦ 1s2 Oxygen ◦ 1s2 2s2 2p4 Electron Configuration Filling Order – Memory Aid What is the electron configuration of Carbon? Write the electron configuration and orbital notation for Sulfur Practice Highest Occupied Level – The highest main energy level (highest n value) that contains an electron Outer shell electrons – electrons in the Highest Occupied Level Inner shell electrons – all those electrons EXCEPT those in the Highest Occupied Level Example – Carbon ◦ 2 inner shell electrons ◦ 4 outer shell electrons Definitions Noble gas – Has full s and p orbitals Noble gas configuration ◦ [symbol] stand for the complete electron configuration of the specified noble gas ◦ Add electrons after noble gas required for element. ◦ Na – [Ne] 3s1 Noble Gases All noble gases have full outer main energy levels ◦ He – 2 electrons (Energy Level n=1) ◦ All others – 8 electrons (Energy Level n = 2 to 7) Important Note Filling Orbtials and the Periodic Table Fill 4s first Then next lowest energy 3d – it fills next Followed by 4p Fourth Period Chromium ◦ Expected - [Ar] 3d4 4s2 ◦ Actual - [Ar] 3d5 4s1 ◦ Why? Two half filled orbitals have more stability and lower energy than one full and one partially full Copper ◦ Expected - [Ar] 3d8 4s2 ◦ Actual - [Ar] 3d10 4s0 ◦ Why? A full d orbital and unfilled s orbital have more stability and lower energy than one full and one partially full 4th Period Exceptions to the Expected Filling Order – KNOW THESE!!!! Deviates from Nb to Ag 5th Block Exceptions to the Expected Filling Order 1. What element has 2 electrons in the p orbitals in the 2nd Energy Level? 2. What is the maximum number of electrons that can be found on the second energy level? 3. What element in the third period has the same outer electron configuration as the element in #1? Practice 1. What element has 5 electrons in the p sublevel on the third energy level? 2. How many total electrons does this element have on the third energy level? 3. What element in the 4th Period has the same outer configuration as this element? More Practice What element has the configuration [Ne]3s1? How many inner shell electrons does this element have? What is the Noble Gas configuration for Al? ◦ How many outer shell electrons? ◦ How many inner shell electrons? Even More Practice Write the electron configuration and Noble Gas configuration for Ti. How many electron containing orbitals in Ti? How many orbitals in Ti are completely filled? Are you Ready for More?