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How are electrons placed in the atom?
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How are electrons placed in the atom?

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This PowerPoint tells you more about the three principles which we have to follow when filling in electrons in electron-in-box diagrams.

This PowerPoint tells you more about the three principles which we have to follow when filling in electrons in electron-in-box diagrams.

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  • 1. How are electrons placed in the atom?
  • 2.
    • Introduction
      • Everybody knows that there are electrons orbiting atoms, but how are they arranged in the atom? 
      • There are actually a set of rules which govern the placement of electrons. 
      • The rules are called AUFBAU Principle, Pauli Exclusion Principle and Hund's Rule. 
      • However, these rules only apply to the ground state of an atom or ion .
  • 3.
    • AUFBAU Principle
      • The lowest energy levels are always filled first
      • Conversely, electrons are lost from the highest energy levels first 
      • The diagram shows the order in which we should fill up the subshells.
    http://www.100ciaquimica.net/images/temas/tema3/ima/aufbau3g.gif
  • 4.
    • Diagram showing different energy levels of various atoms
    Scale/Quantum Number Arrangement of electrons Orbital Elements http://www.welsch.com/gallery/vektor/Energieniveauschema_634.jpg Subshell
  • 5.
    • Pauli Exclusion Principle
      • If there are 2 electrons occupying the same orbital, the 2 electrons must be of opposite spins so as to stay at ground state
    http://santasusana.org/pakelly/G%20Chemistry/Pauli.gif
  • 6.
    • Hund's Rule
      • If multiple orbitals of the same energy are available, Hund's rule states that unoccupied orbitals will be filled before occupied orbitals are filled up by electrons having different spins.
    http://img.sparknotes.com/figures/5/5578bdf1aec90e46e14325a580fdbf6a/fig1_4.gif Element: Carbon
  • 7.
    • Anomalous Electron Configurations
    • Certain atoms do not follow the orbital-filling rules: 
    •  
      • Chromium's electron configuration is [Ar]3 d 5 4 s 1 instead of the expected [Ar]3 d 4 4 s 2   if we are to follow the normal rules
      • Copper's electron configuration is [Ar]3 d 10 4 s 1 instead the expected [Ar]3 d 9 4 s 2  
      • There are others in the heavier d -block metals and the f -block metals. Molybdenum and Rhodium are some examples.
    •  
    • This occurs when there are enough electrons to produce a half-filled set of degenerate orbitals (as in the case of chromium) or to completely fill a d or f subshell (like copper).
  • 8.
    • ANALOGY
    • The seat a Singaporean would take in a bus.
      • Orbital: A set of two seats beside one another.
      • AUFBAU principle: One would try to be as near the front as possible since it requires lesser energy.
      • Pauli exclusion principle: No 2 people are exactly the same.
      • Hund's Rule: People would rather not to sit next to each other.
      • Subshell: A set of orbitals beyond which the force of attraction towards the front is lower than the force of repulsion from other people, when it is not completely full.