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.

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How are electrons placed in the atom?

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

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