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Notes on electronic configuration

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Sure! Here’s an overview of electronic configuration, including key concepts, rules, and examples:

What is Electronic Configuration?

Electronic configuration refers to the distribution of electrons in an atom's orbitals. It describes how electrons are arranged around the nucleus in various energy levels and sublevels.

Key Concepts

  1. Energy Levels and Sublevels:

    • Electrons are arranged in energy levels (n = 1, 2, 3, ...), where 'n' represents the principal quantum number.
    • Each energy level contains sublevels (s, p, d, f) with specific shapes and capacities:
      • s: 1 orbital, can hold 2 electrons
      • p: 3 orbitals, can hold 6 electrons
      • d: 5 orbitals, can hold 10 electrons
      • f: 7 orbitals, can hold 14 electrons

  2. Aufbau Principle:

    • Electrons fill orbitals starting from the lowest energy level to the highest.
    • Order of filling typically follows: 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f, 6d, 7p.

  3. Pauli Exclusion Principle:

    • No two electrons in an atom can have the same set of four quantum numbers. This means that an orbital can hold a maximum of two electrons, which must have opposite spins.

  4. Hund's Rule:

    • Electrons must occupy degenerate (equal energy) orbitals singly first before pairing up. This minimizes electron-electron repulsion and stabilizes the atom.

Writing Electronic Configurations

  • The configuration is written as a sequence of numbers and letters, denoting the energy level and type of orbital, followed by a superscript indicating the number of electrons in those orbitals.

    Example:

    • Oxygen (O, atomic number 8):
      • Configuration: \(1s^2\ 2s^2\ 2p^4\)

Noble Gas Configuration

  • For larger atoms, electronic configurations can be simplified by using noble gas configurations. The configuration starts from the last noble gas preceding the element, making it shorter and easier to write.

    Example:

    • For Rubidium (Rb, atomic number 37), instead of writing all orbitals:
      • Noble gas core: [Kr] (Krypton, atomic number 36)
      • Configuration: \([Kr] 5s^1\)

Examples of Electronic Configurations

  1. Hydrogen (H, atomic number 1):

    • Configuration: \(1s^1\)

  2. Carbon (C, atomic number 6):

    • Configuration: \(1s^2\ 2s^2\ 2p^2\)

  3. Neon (Ne, atomic number 10):

    • Configuration: \(1s^2\ 2s^2\ 2p^6\)

  4. Iron (Fe, atomic number 26):

    • Configuration: \(1s^2\ 2s^2\ 2p^6\ 3s^2\ 3p^6\ 4s^2\ 3d^6\) or in noble gas form: \([Ar] 4s^2\ 3d^6\)

  5. Silver (Ag, atomic number 47):

    • Configuration: \([Kr] 5s^2\ 4d^{10}\)

Conclusion

The electronic configuration of an atom is fundamental to understanding its chemical behavior, including bonding, reactivity, and the formation of ions. By studying these configurations, chemists can predict the outcomes of chemical reactions and the properties of materials.