Question

Can trivalent oxygen exist with positive charge

Answer 1

The situation is analogous to the hydronium ion H3O+ which is also often written with a positive charge on the oxygen atom. This is a formal charge and just arises from a particular way of counting electrons. Chemists have developed a very simple bookkeeping method to represent whether an atom within a molecule or ion is neutral, or bears a positive or negative charge. These integer charges are called formal charges. A formal charge is a comparison of electrons "owned" by an atom in a Lewis structure versus the number of electrons possessed by the same atom in its unbound, free atomic state. For the hydronium ion, each hydrogen has one valence electron, no unshared electrons and two shared electrons in the oxygen-hydrogen covalent bond. Thus, the calculated formal charge on hydrogen is zero. Any hydrogen bearing one covalent bond always has a formal charge of zero. Oxygen has six valence electrons, two unshared electrons in one lone pair and six shared electrons in three oxygen-hydrogen covalent bonds. Thus the calculated formal charge on oxygen is +1. Because this method provides some indication of charge distribution, it is a starting point for determining electron distribution within a molecule or ion and hence gives us a basis to predict chemical and physical properties. However, it is only a crude approximation and more detailed calculation shows that, far from being positive, the oxygen atom in the hydronium ion in fact carries a negative charge of -0.44 and the positive charge is distributed among the three hydrogen atoms.A similar situation will exists for alkyl oxonium ions.