Electron Configuration and Periodic Trends

Evolution of Atomic Theory

Dalton’s Atomic Theory

Dalton’s Atomic Theory did not explain how atoms break down into subatomic particles

J.J. Thompson

found the existence of electrons and created the plum pudding model J.J. Thompson found the existence of electrons and created the plum pudding model

Rutherford

Rutherford discovered the nucleus and proposed the idea of a dense nucleus surrounded by electrons

Bohr

Bohr proposed that electrons are arranged in orbits around the nucleus and that the electrons have a fixed energy so they can’t fall into the nucleus

Quantum Mechanical Model The modern description of electrons in atoms proposed by Schrödinger

Quantum Mechanical Model proposed that the location and energy of an electron could be determined by the Schrödinger wave equation

Quantum Mechanical Model

Quantum Mechanical Model This model tells you that the e is found 90% of the time within a cloud

Quantum Mechanical Model

Quantum Mechanical Model and Atomic Orbitals Principle Quantum Number (n) designates energy levels by n=1,2,3,4….as the electrons move away from the nucleus

Quantum Mechanical Model and Atomic Orbitals Sublevels are found within each energy level and they are designated by s, p, d, and f

Quantum Mechanical Model and Atomic Orbitals

Quantum Mechanical Model and Atomic Orbitals Atomic orbitals make up each sublevel

Quantum Mechanical Model and Atomic Orbitals Each Atomic orbital holds 2 electrons

Quantum Mechanical Model and Atomic Orbitals Chart

Summary Principle Quantum numbers always equal the number of sublevels within that energy level

Summary The number of orbitals within each energy level is n2

Summary The maximum number of electrons that can occupy each energy level is 2n2

Electron Configuration The way electrons are arranged around the nucleus of an atom according to the quantum mechanical model Represented by orbital notation

Electron Configuration Guidelines: 1. Aufbau Principle Electrons enter orbitals of lowest energy first

Electron Configuration 2. Pauli Exclusion Principle An atomic orbital at most describes 2 electrons, and they must be of opposite spin

Electron Configuration 2. Pauli Exclusion Principle

Electron Configuration 3. Hund’s Rule When electrons occupy orbitals of the same energy, one electron occupies each orbital until all electrons are of the same spin, then second electrons can be added

Electron Configuration 3. Hund’s Rule

Electron Configuration Exceptions to the rules Cu and Cr

Electron Configuration Shorthand Notation Energy level (n=1,2,3,…) symbol for sublevel (s, p, d, f) Superscript for electrons Superscripts sum = total electrons

Electron Configuration

Electron Configuration Noble Gas Notation Previous noble gas symbol in brackets Additional orbitals in shorthand

Electron Configuration Noble Gas Notation