What important characteristic do the alkali metals alkaline earth metals have in common?

1 Answer
Jul 2, 2018

Atoms from both groups form cations of limited oxidation states as opposed to transition metals that form ions of more than one possible charge .

  • Alkali metals form ions of charge #+1# whereas
  • Alkaline earth metals form ions of charge #+2#


Most alkali and alkaline-earth elements have low electronegativity and tend to form cations in chemical processes. Magnitudes of consecutive ionization energies of a particular atom offer insights into the various possibilities of its ion formations.


For example, it takes no more than #1, 200 color(white)(l) "kJ"# per mole electrons to empty the valence shell of calcium (the blue line in the diagram) under standard conditions. However, that value would be around #5,000 color(white)(l) "kJ"# when it comes to the removal of inner shell electrons. Energies released during the formation of ionic bonds are typically sufficiently high to drive the removal of both valence electrons in alkali and alkaline-earth metals. Removals of inner shell electrons are energetically-intensive and are nonspontaneous in chemical processes.

Alkali and alkaline-earth cations are energetically stable with an empty valence shell. Atoms of alkali and alkaline-earth elements achieve octets after losing one (alkali) or two (alkaline-earth) electrons such that they minimize the potential energy of the system. Ions of charge #+1# and #+2# are thus the most common components in compounds of these elements.