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Chapter 2: Atomic Theory

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    This chapter reviews atomic orbitals and the periodic properties of atoms.

    Learning Objectives
    • Understand the sizes, shapes, and relative energies of atomic orbitals and how they depend on quantum numbers
    • Identify the number of radial and angular nodes in an atomic orbital
    • Determine the ground state electron configuration and number of unpaired electrons for a given atom
    • Explain periodic trends and their physical origins

    Thumbnail illustrates the electron density of a 3d orbital, generated with the Orbitron

    • Section 2.1: Quantum Numbers and Atomic Wavefunctions
      Atomic orbitals can be described by a set of three quantum numbers. A fourth quantum number defines the orientation of the electrons in that orbital.
    • Section 2.2: Aufbau Principle
      The Aufbau Principle (also called the building-up principle or the Aufbau rule) states that, in the ground state of an atom or ion, electrons fill atomic orbitals of the lowest available energy level before occupying higher-energy levels.
    • Section 2.3: Shielding
      The presence of other electrons in an atom will shield an electron from feeling the full positive charge of the nucleus. The amount of screening is determined by the number other electrons and their location.
    • Section 2.4: Periodic Properties of Atoms
      Periodic trends are specific patterns that are present within the periodic table; these are patterns in properties like electronegativity, ionization energy, electron affinity, atomic radius, melting point, and metallic character. These trends exist because of the similar atomic structure of the elements within their respective group families or periods, and because of the periodic nature of the elements.

    Chapter 2: Atomic Theory is shared under a CC BY-NC-SA 4.0 license and was authored, remixed, and/or curated by LibreTexts.