Section 4: 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

This aufbau diagram shows the energy levels of the various atomic orbitals. Orbitals of greater energy are higher on the diagram. Using Tables Which is of higher energy, a 4d or a 5s orbital? Aufbau Principle (building up), electrons fill the orbitals of lowest energy first.

↑ ↓ s Pauli Exclusion Principle an atomic orbital may describe at most two electrons that must have opposite spins; that is, the electron spins must be paired. ↑ ↓ s

↑ ↓ ↑ ↓ ↑ ↓ px py pz Hund’s Rule electrons occupy orbitals of the same energy with as many of the same spin as possible before opposite spin. ↑ ↓ ↑ ↓ ↑ ↓ px py pz

Electron configuration Element # of electrons Orbital notation Electron configuration Lithium 3 ____ ____ ____ ____ ____ 1s 2s 2p 1s22s1 Beryllium 4 1s22s2 Boron 5 1s22s22p1 Carbon 6 1s22s22p2 Nitrogen 7 1s 2s 2p 1s22s22p3 Oxygen 8 1s22s22p4 Fluorine 9 1s22s22p5 Neon 10 1s22s22p6

Write the electron configuration for phosphorus (P): 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 -Where should we start placing electrons first? -Opposite spin alleviates repulsion. -All single before double. nucleus

valence electrons: 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 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 -Where should we start placing electrons first? -Opposite spin alleviates repulsion. -All single before double. How many valence e–’s in Krypton (Kr)? 8 nucleus

Quick Quiz! 1. Identify the element that corresponds to the following electron configuration: 1s22s22p63s2 Ca Ne Na Mg

Quick Quiz. 2. Write the electron configuration for the atom N. 1s22s22p5 1s22s22p3 1s22s1p2 1s22s22p1

Quick Quiz. 3. What is the first (lowest-numbered) principal energy level in which p orbitals are found? 1 2 3 4

Electron Configurations and the Periodic Table The period number tells you the energy level (remember, the d block is one energy level lower). The group # tells you the # of valence electrons. Group 1 elements have 1. Group 7A have 7.

Noble Gas Core Configuration Noble Gases are group 18 Na: 1s2 2s2 2p6 3s1 Ne: 1s2 2s2 2p6 Noble gas e- config for Na: [Ne] 3s1 Ne

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

P Lewis dot diagrams valence e–’s are shown as dots around the symbol of the element Phosphorus (P): 1s2 2s2 2p6 3s2 3p3 # valence e–’s: ___ 5 [Ne]3s2 3p3 Group # : ___ 5A Lewis dot diagram: P

Br Lewis dot diagrams valence e–’s are shown as dots around the symbol of the element Bromine (Br): 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p5 [Ar]4s2 3d10 4p5 # valence e–’s: ___ 7 Group # : ___ 7A Lewis dot diagram: Br