Electron Configurations

2s 2p 1s 3s Electron energy levels have sublevels of different shapes orbital Nucleus 2p orbitals 1s orbital 3s orbital

How do electrons fill these orbitals? Electron Configurations: location of e–’s in different orbitals 3 principles describe the electron configuration of any atom: the aufbau principle the Pauli exclusion principle and Hund’s rule The 3 rules work “in concert”. So you must be able to use any one when it is required.

e–’s fill orbitals of lowest energy first Aufbau Principle: (building up) e–’s fill orbitals of lowest energy first -Where should we start placing electrons first? -Opposite spin alleviates repulsion. -All single before double. nucleus

Arrows go as you progress along the Periodic Table.

Pauli Exclusion Principle: (up/down) e–’s in same orbital have opposite spin -Where should we start placing electrons first? -Opposite spin alleviates repulsion. -All single before double. nucleus

e–’s pair after one in each same E orbital Hund’s Rule: (up/up/up/ down/down/down) e–’s pair after one in each same E orbital -Where should we start placing electrons first? -Opposite spin alleviates repulsion. -All single before double. nucleus

Write the electron configuration for Phosphorus (P): nucleus

Write the electron configuration for Selenium (Se): 1s22s22p63s23p64s23d104p4 nucleus

Hund’s Rule Exception 1: Copper (Cu) 1s22s22p63s23p64s13d10 nucleus

Hund’s Rule Exception 2: Chromium (Cr) 1s22s22p63s23p64s13d5 nucleus

1s2 2s2 2p6 3s2 3p3 valence electrons: Write the electron configuration for phosphorus (P): 1s2 2s2 2p6 3s2 3p3 valence electrons: e–’s in the outer most (highest) energy level How many valence e–’s in phosphorus (P)? 5 nucleus

Write the electron configuration for Krypton (Kr): 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 (3d fills after 4s) -Where should we start placing electrons first? -Opposite spin alleviates repulsion. -All single before double. nucleus

Write the electron configuration for Krypton (Kr): 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 valence electrons: e–’s in the outer most (highest) energy level - At left has a lack of subtlety. For now, ignore d electrons. Highest open s and p only. -Where should we start placing electrons first? -Opposite spin alleviates repulsion. -All single before double. How many valence e–’s in Krypton (Kr)? nucleus 8

Write the full electron configuration for Gallium (Ga), atomic number 31. 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p1 [Ar] 4s2 3d10 4p1 OR noble gas core configuration Ar

P Br valence e–’s: Lewis dot diagram: e–’s in highest energy level valence e–’s as dots Phosphorus (P): Bromine (Br): 1s2 2s2 2p6 3s2 3p3 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p5 [Ne]3s2 3p3 [Ar]4s2 3d10 4p5 # valence e–’s: ___ 5 # valence e–’s: ___ 7 Group # : ___ 5A Group # : ___ 7A Lewis dot diagram: Lewis dot diagram: P Br

Quick Quiz! 1. Which element has following electron configuration: 1s2 2s2 2p6 3s2 Ca Ne Na Mg How many valence e–’s? 2 Group 2

Quick Quiz. 2. Write the electron configuration for an atom of oxygen (O). 1s2 2s6 1s2 2p6 1s2 2s2 2p4 1s2 2s3 2p3 How many valence e–’s? 6 Group 16 (6A)