Chapter 19.1 oxidation number or oxidation state – the number of electrons that must be added or removed from an atom in a combined state to convert the atom into the elemental form oxidation numbers are not charges, they are just used to indicate the general distribution of electrons in a molecular compound or polyatomic ion there are 10 rules for assigning oxidation numbers

Chapter 19.1 Shared electrons are assumed to belong to the more electronegative atom in the bond. Atoms in a pure element have an oxidation number of zero. ex. Na, O2, P4 3. Fluorine always has an oxidation number of -1 in all its compounds.

Chapter 19.1 4. The more electronegative element in a binary molecular compound is given the number equal to the negative charge it would have as an anion. The less electronegative atom is given the oxidation number equal to the positive charge it would have as a cation. ex. SF6

Chapter 19.1 5. Oxygen almost always has an oxidation number of -2, except when bonded with fluorine when its oxidation number is +2. ex. SO3 OF2 6. Hydrogen has an oxidation number of +1 in all compounds with atoms more electronegative than it. It has an oxidation number of -1 in compounds with metals. ex. H3PO4

Chapter 19.1 7. The sum of the oxidation numbers of all atoms in a neutral compound is zero. 8. The sum of the oxidation numbers of all atoms in a polyatomic ion is equal to the charge of the ion. ex. OH- 9. Oxidation numbers can also be assigned to atoms in an ionic compound.

Chapter 19.1 10. A monatomic ion has an oxidation number equal to the charge of the ion. ex. NaCl

Chapter 19.1

Chapter 19.1 oxidation – process in which the atoms or ions of an element experience an increase in oxidation state it loses electrons an atom or ion is oxidized if it loses an electron ex. Na → Na+ + e-

Chapter 19.1 reduction – process in which the atoms or ions of an element experience a decrease in oxidation state it gains electrons an atom or ion is reduced if its oxidation number decreases ex. Cl2 + 2e- → 2Cl-

Chapter 19.1 oxidation-reduction reaction – any chemical process in which elements undergo changes in oxidation number also known as a redox reaction oxidation number must change to be a redox reaction can be written as 2 half reactions half-reaction – part of the reaction involving oxidation or reduction alone

Chapter 19.1 ex. Cu + 2NO3- + 4H+ → Cu2+ + 2NO2 + 2H2O Cu → Cu2+ + 2e- oxidation half-reaction 2NO3- + 2e- + 4H+ → 2NO2 + 2H2O reduction half-reaction HCl + NaOH → NaCl + H2O

Chapter 19.1 Hwk due Monday Pg 612 2-7