One of the questions I got wrong on a chemistry Kahoot question was

(1) Potassium is in group $1$, what is its oxidation number?

(a) -1

(b) +1

(c) +2

(d) -2

I don't remember what an "oxidation number" is... And what do they mean by group $1$? I don't quite remember learning that.

  • $\begingroup$ All about potassium at Wikipedia en.wikipedia.org/wiki/Potassium Here is link to Wikipedia article on the periodic table. Notice group numbers along top of first figure. en.wikipedia.org/wiki/Periodic_table $\endgroup$ – MaxW Sep 29 '16 at 22:53
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    $\begingroup$ Hm... Our teacher said that the number above was the number of valence electrons the elements had. (Paying only attention to the units place)... So a group number just tells you the number of electrons in the outer shell? $\endgroup$ – Frank Sep 29 '16 at 22:54

Potassium's oxidation number is +1, oxidation numbers are just hypothetical charges that an atom would have if the compound is ionic(This is not always the case),but it's useful for keeping track of electrons. In this case it means that the Potassium atom losses one electron when forming compounds. Chemical elements are arranged in groups where the number with the letter(e.g.,1A,2A,3B,etc.) shows how many valence electrons an atom has, Group 1A(The first column to the left on the periodic table) has one electron on its valence shell so it tends to lose that electron in order to get a noble gas's electronic configuration and that makes sense given Potassium's oxidation number. There's the periodic table with the arrangement I'm talking about

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  • $\begingroup$ Wait, so if Potassium wants to lose an electron, shouldn't it be -1? What does oxidation number mean? $\endgroup$ – Frank Sep 30 '16 at 2:36
  • $\begingroup$ Oxidation Numbers are like charges, when a neutral atom (Same number of protons and electrons) loses one electron there would be one proton in excess so the charge becomes +1; on the other hand if an atom gains one electron there would be one electron in excess so the charge becomes -1. $\endgroup$ – Rotvie Sep 30 '16 at 3:15
  • $\begingroup$ Oh, so when a question asks for an element's oxidation number, it's really just asking for the element's charge? $\endgroup$ – Frank Sep 30 '16 at 3:19
  • $\begingroup$ Kind of, you can find oxidation numbers of each element following certain rules such as oxygen when forming oxides has an oxidation number of -2 mostly,all alkali elements have an oxidation number of +1,etc. The sum of all oxidation numbers gives you the total charge of the compound(0 if it's neutral) $\endgroup$ – Rotvie Sep 30 '16 at 3:32
  • $\begingroup$ There you have the tendencies for oxidation numbers of each element thecatalyst.org/oxnotabl.html $\endgroup$ – Rotvie Sep 30 '16 at 3:39

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