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Advanced Atomic Theory Review

Key Concepts in Atomic Theory

  • Atomic Number: The number of protons in an atom's nucleus, which defines the element.

  • Mass Number: The total number of protons and neutrons in the nucleus of an atom.

  • Isotopes: Variants of a given element that have the same number of protons but different numbers of neutrons, affecting their mass.

  • Ions: Charged atoms that occur when atoms gain or lose electrons.

    • Cations: Positively charged ions (loss of electrons).

    • Anions: Negatively charged ions (gain of electrons).

  • Quantum Mechanics: Describes electrons in terms of probability distributions rather than fixed orbits around the nucleus.

  • Energy Levels: Electrons occupy specific energy states, and energy is absorbed or emitted when electrons transition between these levels.

  • Electron Configuration: The distribution of electrons among the various orbitals in an atom as defined by quantum mechanics.

Important Formulas

  • Average Atomic Mass: [ \text{Average Atomic Mass} = \sum (\text{fraction of isotope} \times \text{mass of isotope}) ]

  • Energy of a Photon: [ E = h u ]Where ( E ) is energy, ( h ) is Planck's constant (6.626 x 10^-34 J·s), and ( u ) is the frequency of radiation.

  • Bohr's Energy Level Formula: [ E_n = -\frac{KZ^2}{n^2} ]Where ( E_n ) is the energy of the electron at level n, ( K ) is a constant, ( Z ) is the atomic number, and ( n ) is the principal quantum number.

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Electron configuration is typically written in a format that represents the distribution of electrons among the various atomic orbitals. The format includes the principal quantum number, the type of orbital, and the number of electrons in that orbital.

Here’s how to format it:

  1. Principal Quantum Number (n): Indicates the main energy level.

  2. Orbital Type: Designated by the letters s, p, d, f.

  3. Electron Count: The number of electrons in each orbital is indicated as a superscript.

For example, the electron configuration for carbon (atomic number 6) is:

  • 1s² 2s² 2p²This denotes:

    • 2 electrons in the 1s orbital

    • 2 electrons in the 2s orbital

    • 2 electrons in the 2p orbital

As you assign electrons to orbitals, remember that according to the Aufbau principle, electrons fill orbitals in order of increasing energy.