Electron Configuration: Aufbau Principle

Warm Up Activity

• Define the mass number of an elements
• Identify the atomic number of calcium
• Calculate the number of neutrons in Silicon

The Atom

• Recognize and compare the relative energies of s, p, and d orbitals
• Apply principles (Aufbau, Hund's rule, Pauli Exclusion) to determine electron configuration
• Compare and rank the relative energies of s, p, and d orbitals and explain their significances.
• Construct full and condensed electron configurations for elements and ions up to Z=36

Electron Configuration

• Electron configurations show where the electrons are located within an atom.
• Each energy level or shell surrounding an atom is given a letter: s, p, d and f.
• Each orbital can hold up to 2 electrons

Electron Configuration Principles

• Based on the Aufbau principle, Pauli Exclusion Principle, and Hund's Rule

Aufbau Principle

• Electrons occupy the lowest energy orbitals (or shells) first.
• Principle energy level (n = 1,2,3,...) corresponds to the energy levels of an electron within an atom.

Electron Configuration: Levels/Sublevels

• Each principal energy level is divided into sub-levels: s, p, etc.
• In each sublevel the electrons are found within specified orbitals.
• The order of energy levels and sublevels when creating an electron configuration is: 1s² → 2s² → 2p⁶ → 3s² → 3p⁶ → 4s² → 3d¹⁰ → 4p⁶

Example: Silicon Configuration

• Silicon has 14 electrons, so the full electron configuration begins at 1s.

Sub-level Orbitals and Shapes

• s

  • Contains 1 orbital
  • Spherical shape
  • Starts at the 1st principal energy level

• p

  • Contains 3 orbitals
  • Three tear shapes
  • Starts at the 2nd principal energy level

• d

  • Contains 5 orbitals
  • Five different shapes
  • Starts at the 3rd principal energy level

• f

  • Contains 7 orbitals
  • Seven different shapes
  • Starts at the 4th principal energy level

• Each orbital can hold 2 electrons

Check In

• If each orbital (region of space) can hold a maximum of 2 electrons
  • How many electrons fit in each orbital? s, p, d f

Question

• Write the electron configuration of the following elements
  • Sodium
  • Magnesium
  • Boron
  • Neon
  • Sulfur

Layout of the Periodic Table

• The energy sublevel filled or partially filled last aligns with the location of that element within the periodic table.
• Phosphorus is in the p block so the electron configuration ends at 3p.
• P=15: 1s²2s²2p⁶3s²3p³

Electron Configurations, Magnesium

• Electron configuration: 1s²2s²2p⁶3s²
  • Condensed electron configurations: [Ne]3s²
• Guidelines for condensed configurations
  • Check for the closest noble gas to the left of the element.
  • Input noble gas in square brackets and then state the location of the remaining outer electrons in the atom.

Aufbau/ Orbital Diagrams

• Are a visual representation of electron configurations.
• Gives more information specific to the individual electrons involved.
• Each square represents an orbital and sublevels that contain more than one orbital appear together. -d sublevels, for example, contain 5 orbitals and will have 5 associated squares

Pauli Exclusion Principle

• Each orbital can hold a maximum of two electrons.
  • An orbital can contain 0, 1, or 2 electrons.
• Each electron appears to spin around an axis.

Electron Spin

• Spin occurs in two directions, represented as up and down arrows (↑↓).
• The first drawn electron to enter the orbital is drawn as an upwards pointing half-arrow.
• The second electron must have an opposing direction to the first electron.

Hund’s Rule

• One electron enters each orbital until each contains an electron with the same spin direction.
• A second electron in the opposite direction can then enter any of the orbitals.

Understand electron configurations using the Aufbau principle, Pauli Exclusion Principle, and Hund's Rule. Learn how electrons fill energy levels and orbitals. Determine electron configurations for elements and ions.