Oxidation States (3.1.6 )

Bonding is often not ionic or covalent, but rather a continuum with unequal sharing of electrons.

Oxidation States/Oxidation numbers are used to represent the charge of an atom if it was composed of ions. It also shows the number of electrons being transferred or shared when bonding.

E.x. Water ($H_2O$)--> "Covalent" . If it was Ionic, Oxygen ( $O^{-2}$ ) would gain two electrons and hydrogen ( $H^{+1}$)would each lose one. Thus,

Hydrogen has oxidation state of +1. And Oxygen is assigned an Oxidation state of -2.

Rules to deduce oxidation states of atoms

1. Oxidation state of any free element is zero.

2. The sum of the oxidation States of all atoms in a neutral compound is zero.

3. Sum of Oxidation States of all atoms in a polyatomic ion is equal to the charge of the ion.

4. Oxidation state of fluorine is -1 in all compounds.

5. The oxidation state of group 1 --> + 1 / Oxidation state of group 2 --> +2 ALWAYS

6. Oxygen always have oxidation state of +2, except in $OF_2$where flourine is more electronegative ( Oxygen has state of +2 here ), and in peroxides $H_2O_2$( Oxygen has state of -1 here ), the oxidation state is always -1.

7. Hydrogen's Oxidation state is:

   1. +1 when combined w/ more electronegative elements ( most non-metals )

   2. -1 when combined w/ less electronegative elements ( metals ). When this happens, this compound is called a Hydride Ion.

Acid rain & Ocean Acidfication:

• Water generally has pH of $7.0$ neither acidic or basic, but w/ Carbon Dioxide, it forms a weak acid.

$CO_2(g) + H_2O(l) \rightarrow HCO_3 (aq )$

More Carbon Dioxide means more Carbonic Acid into the ocean, affecting the health of coral reef.

The pH of rainwater is 5.6. But for other Oxides, like Nitrogen Oxide ($NO$ ) & Sulfur Dioxide ( $SO_2$ ) the case is different: Their rain can have a pH less than 5.6 which is called acid rain.

These oxides can come from volcanos, decomposing vegetation, and industrial processes.

The nitrous & sulfurous acid though just oxides back into the nitric acid & Sulfuric Acid.