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How Do You Deduce The Electronic Configuration Of Iodine From Its Position In The Periodic Table?

posted Oct 9, 2016, 8:55 AM by Grace Ong   [ updated Oct 25, 2016, 2:15 AM ]

The following post was first posted on Blogger on Wednesday, 10 June 2015.



As a teacher, not only do I focus on the teaching of concepts, I also pay particular attention to my students’ problem solving techniques.

For example, my students were once asked to write the electronic configuration of iodine. The following was what I found scribbled on their scripts. 

student answer 1 - applying Aufbau Principle                    student answer 2 - applying Aufbau Principle

Apparently, many students took the trouble of applying the Aufbau Principle to determine the order in which all 53 electrons of iodine are filled, which was completely unnecessary (and time-consuming)!

The quickest way to write the electronic configuration of iodine, or any element, is to refer to its position in the Periodic Table.

Iodine is a Group 17 (old IUPAC: Group VIIA) element, and all Group 17 elements have an outer electronic configuration of ns2 ns5, where n is the valence quantium shell corresponding to the period in which the element is in.

Since iodine is a Period 5, Group 17 p-block element, its seven valence electrons are found in the n = 5 shell, and its electronic configuration ends with 5s2 5p5.

position of iodine in the Periodic Table

The complete electronic configuration of iodine, using the spdf notation, is therefore

spdf electronic configuration of iodine 1

If you use the noble gas notation, note that the noble gas in Period 4 is krypton. (Since iodine is in Period 5, you should not use the noble gas in Period 5, xenon!)

Kryton and iodine is separated by
  • two Period 5 s-block elements, which corresponds to the filling of the 5s orbital, and
  • ten Period 5 d-block elements, which corresponds to the filling of the five 4d orbitals.
Thus the electronic configuration of iodine, using the noble gas notation, is [Kr] 4d10 5s2 5p5.

Note:
  1. Although the filling of electrons is ordered in terms of energy according to the Aufball Principle, orbital sets are numbered by the principal quantum shell.
  2. Thus the full electronic configuration of iodine should be written as

    spdf electronic configuration of iodine 2
    and not 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p5.
  3. Using the noble gas core configuration, the electronic configuration of iodine is written as [Kr] 4d10 5s2 5p5. Answers like [Kr] 5s2 4d10 5p5 or the following will not be accepted.

    student answer - incorrect spdf notation for iodine

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