Electron Configuration

Why we study electrons Knowing the position of electrons helps us with many topics: Why chemical reactions occur Why some atoms are more stable than others Why some elements react with only certain atoms Goal for this topic: We want to know how many electrons an atom has, and where they’re located.

The Big (actually small) Picture! “Electron Cloud” - Energy Levels ( 1 – 7) - Sublevels (S,P,D,F – Shapes) - Orbitals (Specific Orientations– X/Y/Z axis)

- S Sublevel – Think Sphere What the orbitals look like… - S Sublevel – Think Sphere - P Sublevel – Figure 8 P Sublevel- X Axis P Sublevel- Y Axis Nucleus P Sublevel- Z Axis S Sublevel

Periodic Patterns s p d (n-1) f (n-2) 1 2 3 4 5 6 7 6 7 © 1998 by Harcourt Brace & Company

Orbital Diagrams Orbital Diagrams are Visual illustrations that show the order that electrons will follow as they fill in the electron cloud. We start from the bottom and work your way up. That symbolizes starting on the first energy level and work outward.

General Rules Aufbau Principle Electrons must fill the lowest sublevel available. (Letters - S,P,D,F) You cannot skip any sublevels. It’s like the Alphabet!

General Rules Pauli Exclusion Principle Each orbital (each box on the diagram) can hold only TWO electrons, and the electrons have opposite spins.

General Rules WRONG RIGHT Hund’s Rule Within a sublevel, place one electron in each orbital with the same spin before pairing them with a second electron. - “Empty Seat Rule” WRONG RIGHT

A Few things to know… You are drawing arrows, and they represent electrons. (Neon has 10 electrons so you will need to draw 10 arrows.) Divided up into different sublevels containing a specific number of orbitals. KNOW THIS INFO! - The S sublevel has only 1 orbital= total of 2 e- - The P sublevel has 3 orbitals = total of 6 e- - The D sublevel has 5 orbitals = total of 10 e- - The F sublevel has 7 orbitals = total of 14 e-

Practice - Fill in the orbital diagram for Magnesium

Electron Configuration An atom’s electron configuration… Describes the location of electrons within the atom Identifies the shape of the electron clouds - regions where the electrons are held. Uses numbers and letters to describe electrons’ location and which electron cloud it is part of.

1s2 The Format: The “s” tells you the electron’s cloud shape. In this case it’s a spherically shaped cloud. It is called the s sublevel. Sublevel = Shape 1s2 The “2” simply tells you how many electrons are in this cloud. The “1” tells you how far from the nucleus the electrons can go. In this case 2 electrons are creating the cloud. In this case, its in the 1st energy level, which is the closest level to the nucleus. Note: Every orbital can only hold 2 electrons. They must have opposite spins.

Connection b/w Orbital Diagram and Electron Configuration 1s 2s 2p Electron Configuration 1s2 2s2 2p4

Configuration Practice Problem s p 1 2 3 4 5 6 7 d (n-1) f (n-2) 6 7 Zinc:

Noble Gas Configuration Steps: Shorthand Configuration This is a shorter way to do e- configurations Steps… 1) Find the noble gas (group 18) that precedes and comes before the element you are doing. 2) To begin, put the symbol of that noble gas in [brackets] 3) Starting with that noble gas, continue the electron configuration until you get to the element in question.

1s2 2s2 2p3 Nitrogen: [He] 2s2 2p3 B. Notation Nitrogen: Longhand Configuration Nitrogen: 1s2 2s2 2p3 Valence Electrons Core Electrons Shorthand Configuration Nitrogen: [He] 2s2 2p3

C. Shorthand practice Example - Sulfur [Ne] 3s2 3p4

C. Shorthand practice Example - Germanium [Ar] 4s2 3d10 4p2

Practice these in shorthand Tin (Sn) Uranium (U)