Electron configuration and energy levels are key to understanding atomic structure. They explain how electrons are arranged around the nucleus and why elements behave the way they do. This knowledge forms the basis for predicting chemical reactions and bonding.
These concepts build on earlier ideas about atomic structure. By learning about electron arrangements and energy states, we can better grasp how atoms interact and form compounds. This sets the stage for understanding chemical behavior and properties.
Electron Arrangement Principles
Fundamental Principles of Electron Configuration
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Aufbau principle dictates electrons fill orbitals from lowest to highest energy
Follows the 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 set of quantum numbers
Limits each orbital to a maximum of two electrons with opposite spins
Hund's rule requires electrons to occupy orbitals of equal energy individually before pairing
Maximizes the number of unpaired electrons in degenerate orbitals
Electron configuration notation represents the arrangement of electrons in an atom
Uses numbers, letters, and superscripts to show electron distribution (1s² 2s² 2p⁶)
Applications and Exceptions
Noble gas configuration serves as a shorthand for inner shell electrons
Simplifies notation for elements with many electrons ([Ar] 4s² 3d¹⁰)
Exceptions to Aufbau principle occur in transition metals and lanthanides
Chromium (Cr) has [Ar] 4s¹ 3d⁵ instead of [Ar] 4s² 3d⁴
Copper (Cu) has [Ar] 4s¹ 3d¹⁰ instead of [Ar] 4s² 3d⁹
Orbital diagrams visually represent electron configurations
Use boxes to represent orbitals and arrows for electrons (↑↓)
Electron Energy Levels
Structure of Atomic Energy Levels
Energy levels represent distinct electron shells around the nucleus
Numbered from 1 (closest to nucleus) outward (1, 2, 3, etc.)
Electron shells consist of orbitals with similar energy
K shell (n=1), L shell (n=2), M shell (n=3), and so on
Orbitals describe the probability of finding an electron in a specific region
s orbitals are spherical, p orbitals are dumbbell-shaped
d orbitals have more complex shapes (cloverleaf, doughnut)
Sublevels within each energy level have specific shapes and orientations
s sublevel (1 orbital), p sublevel (3 orbitals), d sublevel (5 orbitals), f sublevel (7 orbitals)
Electron Behavior and Energy States
Principal quantum number (n) determines the main energy level
Ranges from 1 to 7 for naturally occurring elements
Excited states occur when electrons absorb energy and move to higher orbitals
Electrons emit photons when returning to ground state
Quantum mechanical model describes electron behavior probabilistically
Electrons exist in "electron clouds" rather than fixed orbits
Energy of orbitals increases as n increases and l increases
4s has lower energy than 3d due to electron-electron repulsion
Electron Types
Valence Electrons and Chemical Behavior
Valence electrons occupy the outermost shell of an atom
Determine chemical properties and reactivity of elements
Number of valence electrons relates to an element's group in the periodic table
Group 1 (alkali metals) have 1 valence electron
Group 18 (noble gases) have 8 valence electrons (except helium with 2)
Valence electron configuration influences bonding behavior
Elements tend to gain, lose, or share electrons to achieve noble gas configuration
Electron dot diagrams represent valence electrons visually
Dots around element symbol show number and arrangement of valence electrons
Core Electrons and Atomic Properties
Core electrons occupy inner shells closer to the nucleus
Less involved in chemical reactions but affect atomic size and ionization energy
Effective nuclear charge increases across a period due to core electrons
Results in smaller atomic radii and higher ionization energies
Shielding effect of inner electrons reduces the pull of the nucleus on outer electrons
Causes atomic radius to increase down a group
Core electrons contribute to an atom's overall electron configuration
Influence the energy levels and orbitals available for valence electrons