Recently while self-studying my chemistry book, it dawned on me that metals form basic oxides and nonmetals forma acidic oxides. Why is this?


1 Answer 1


It is one of the characteristics of the metals as for electrical conductivity, heat conductivity, mechanical properties. All these basically originate from the outer electrons to be "loosely" bound to the nucleus, when compared to non metals. Bonds in metal oxides are ionic, with positive charge on the metal. The same is for their hydroxides, i.e. their compounds containing an OH group. This leads to their basic dissociation in water giving the stable hydroxide ion.

Contrary non metals have tightly bound electrons and are prone to fill their outer shell (Octet rule). On reaction with a non metal as oxygen the situation is therefore a bit more complicated depending on what specific element the non metal is. Non metals oxides are essentially molecular, although the covalent bond is polar to various extents. However, their compounds containing an OH group will retain electrons on the fragment consisting of the two non metals (of which, one is oxygen of course) leading to acid reaction, i.e. H+

(Note that HClO would be better wrote as ClOH).

It should be clear that things are going as ionisation potential - electron affinity - atom size (distance of the outer electrons from the nucleus). For a better explanation I would need more time, it is basically a big chapter of introductory general chemistry, which goes under the name of periodic law and properties of the elements, or something like that.

  • $\begingroup$ Why HCIO would be better wrote as CIOH? $\endgroup$
    – Sara Asfar
    Commented Jul 14, 2017 at 17:22
  • $\begingroup$ It does not mean you have to abandon writing HClO. The same is true for H2SO4, etc. They are perfect as minimal formula, indicating the exact number and nature of the atoms forming the molecule. I wanted to point out that in the frame of my answer would better to think of the structural formula or even the Lewis structure of the non metal acid. H+ in the acid reaction is coming from the dissociation of a H-O bond rather than a not existing (in water) H-Cl one. Look for HClO, or H2SO4 etc Lewis formulae. Hope this help. $\endgroup$
    – Alchimista
    Commented Jul 14, 2017 at 17:48
  • $\begingroup$ Moreover what you concluded is right. Just you will find out that acid base reactions do not always directly involve protons exchange or water. There are reaction based on electron pair sharing between Lewis acid and bases. If a metal is involved in that, it is in an oxidation states that actually it is not a metal anymore. You will soon notice (or be teached) amphoterism and finer details. $\endgroup$
    – Alchimista
    Commented Jul 14, 2017 at 18:10
  • $\begingroup$ @SaraAsfar see this: chemistry.stackexchange.com/questions/53568/… $\endgroup$ Commented Jul 15, 2017 at 4:58
  • $\begingroup$ Well nice. As you see one should not confuse notation with "reality". Just I made clear I wasn't speaking about notation. At the and everything is Ok saying that benzene has (minimal) formula C6H6 but no one will conclude that it consists of 6 carbon followed by 6 hydrogens in lane :) $\endgroup$
    – Alchimista
    Commented Jul 15, 2017 at 12:18

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