The oxidation and reduction states of elements Redox The oxidation and reduction states of elements

Oxidation Oxidation is the loss of an electron Oxidizing agent – oxidizes other atoms, is reduced in the process Oxygen Powerful oxidation agent Not involved in ALL oxidations, just considered to be one the main culprits.

Reduction Reduction agent – reduces other atoms, is oxidized in the process Reduction is the gain of an electron

O.I.L.R.I.G. OIL RIG OXIDATION IS LOSING ELECTRONS REDUCTION GAINING ELECTRONS

Oxidation Number S S S S S S S S Atoms by themselves have an oxidation number of 0 This is true even for diatomic and larger monospecific (same element) elements such as H2 and S8 When in a polyatomic molecule elements typically will have a standard oxidation number based upon the electronegativity of the element. S S S S S S S

Oxidation Number S S S S S S S S Higher Electronegativity – the lower the oxidation number Oxygen – Upper right of periodic table – high oxidation number – normally 2- Cesium – Lower left of periodic table – low oxidation number – normally 1+ S S S S S S S

Oxidation Number Monoatomic and Polyatomic Ions normally keep their charge. K+ Cl- Oxygen is always 2- except O2 both atoms are 0 And peroxides such as H2O2 where O is 1- Hydrogen is almost always 1+ except when it combines with an alkaline metal where it is -1 and H2 where it is 0 Florine is always -1 The combined oxidations numbers will always equal 0 for a neutral compound or the ionic charge for a polyatomic ion.

Oxidation Trends – Periodic Table

Oxidation States- Oxidation State – the oxidation number of an atom in a chemical bond. Very similar to Ionic Charges Exists in both covalent and ionic bonds. H O Na Cl

Oxidation States in Formula O2 + 2 H2  2 H2O Oxygen oxidizes Hydrogen and gains 2 electrons. Hydrogen Reduces Oxygen and looses 2 electrons. Oxygen is 2- Each Hydrogen is 1+

Oxidation without Oxygen Even without oxygen – oxidation can occur Oxidation could mean – acting like oxygen would F2 + H2  2 HF Here – Oxygen is not present – Hydrogen looses electrons and Fluorine gains electrons H F

Redox Redox Reduction + Oxidation These reactions are considered “redox” (“red”uction + “ox”idation) They do not happen in isolation. Reduction + Oxidation Redox

Determining oxidation numbers for elements without rules. Nonspecific oxidation numbers Based on the whole charge of the compound or polyatomic ion. NO(g) has O = -2 N = +2. NO2(g) has O = -2 * 2 = -4 N = +4. SO42- has O = -2. S + 4(-2) = -2 Solving the equation gives S = -2 + 8 = +6. K2Cr2O7 has K = +1 and O = -2. 2(+1) + 2 Cr + 7(-2) = 0; 2 Cr = 12; Cr = +6.

Determine the charges for the elements in the below compounds Determine the charges for the elements in the below compounds. List in your notes. 1. N in N2O3 2. S in H2SO4 4. C in CO 5. Na in NaCl 6. H in H2O 7. Ba in BaCl2 8. N in NO2-