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Alkali metal reactivity

  1. Oct 22, 2015 #1
    We know that lithium, sodium and potassium tarnish when exposed to air, but rubidium and cesium catch on fire. Why is there such a huge jump in reactivity between Rb and K?
  2. jcsd
  3. Oct 22, 2015 #2


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    Good question. Because going down in the periodic system, the ions get bigger and bigger, ionization energies become smaller. So it's easier to start a reaction with the bigger guys.
    Does that make it clearer ?
  4. Nov 2, 2015 #3
    BvU has it right. There's not really a "huge jump" in reactivity ... it's just a matter of reaching a threshold in the rate of energy release, to a point where things proceed differently. Expose K to hot air, or to a higher concentration of oxygen, and it will behave like Rb.
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