Electron configuration is the blueprint of atomic structure, showing how electrons are distributed in orbitals. It's key to understanding chemical behavior and periodic trends. This topic builds on quantum mechanics to explain electron arrangement.

Mastering electron configuration helps predict an element's properties and reactivity. We'll learn about principles like Aufbau and Hund's rule, and how to write configurations using notation and diagrams.

Electron Configuration Principles

Fundamental Principles of Electron Arrangement

• Aufbau principle dictates electrons fill orbitals from lowest to highest energy
• Electrons occupy subshells in order: 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f, 6d, 7p
• Pauli exclusion principle states no two electrons in an atom can have the same four quantum numbers
• Maximum of two electrons can occupy each orbital, must have opposite spins
• Hund's rule requires electrons in orbitals of equal energy to occupy separate orbitals before pairing
• Unpaired electrons in separate orbitals of equal energy must have parallel spins

Electron Configuration Notation and Representations

• Electron configuration notation uses noble gas core notation to simplify writing
• Shorthand notation includes [Noble Gas] followed by valence electron configuration
• Full notation lists all occupied orbitals with superscript numbers indicating electron count
• Orbital box diagrams visually represent electron distribution in orbitals
• Arrows in orbital box diagrams indicate electron spin (up or down)
• Superscript 1 denotes one electron in an orbital, while 2 indicates a filled orbital

Electron Types and Orbitals

Valence and Core Electrons

• Valence electrons occupy the outermost shell of an atom
• Valence electrons participate in chemical bonding and reactions
• Number of valence electrons determines an element's chemical properties
• Core electrons reside in inner shells closer to the nucleus
• Core electrons typically do not participate in chemical reactions
• Core electrons shield valence electrons from the full nuclear charge

Orbital Diagrams and Electronic States

• Orbital diagrams visually represent electron distribution in atomic orbitals
• s orbitals represented as single boxes, p orbitals as three boxes, d orbitals as five boxes
• Arrows pointing up (↑) or down (↓) indicate electron spin in orbital diagrams
• Ground state configuration represents the lowest energy arrangement of electrons
• Excited states occur when electrons occupy higher energy orbitals than normal
• Electrons in excited states can return to ground state by releasing energy (photons)

Advanced Electron Configuration Concepts

• Electron configurations of transition metals often deviate from expected patterns
• d orbitals can be partially filled before s orbitals in some transition metals (chromium, copper)
• Lanthanides and actinides involve filling of f orbitals, leading to complex configurations
• Ionization changes electron configuration by removing outer electrons
• Electron affinity measures an atom's tendency to gain electrons
• Periodic trends in electron configuration influence atomic size, ionization energy, and electronegativity