I was taught that reactivity increases down a group in Gr 1 and Gr 2 elements, but I never understood why. Would anyone be able to please clarify this? Is the same true for non-metals as well such as the elements in Groups 5, 6, and 7? Thanks.

The outermost electrons define chemical properties (keeping in mind that transition elements mix up their outermost shells) and, at heavier elements, these electrons are on shells less strongly bonded to the nucleus. Heavier elements leave their outer electrons more easily. You can check the ionization energy of the elements, there:

http://www.webelements.com/caesium/atoms.html

click up right on neighbour elements to compare.

 

"Reactivity" has different meanings... A metal is more reactive when it loses electrons readily, and an oxidizer when it picks electrons readily, so oxidizers (halogens etc) are more reactive when lighter.

 

Chemistry isn't that simple, and the effect is just a general idea with many exceptions. One might expect reactive elements to make strong bases or acids, but HF is weaker than HCl, the next HBr, HI following the expected order. Salt solubility neither is a simple consequence of reactivity. Neither is displacement in a solution a direct consequence of reactivity.

 

So beware of a simplistic representation of reactions that would be determined by reactivity comparisons only: they're not.

Edited April 15, 201312 yr by Enthalpy