A New Unit Oxidation & Reduction (Redox)

Do you remember the five kinds of reactions? Synthesis Decomposition Combustion Single replacement Double replacement A + B → AB AB → A + B A + O 2 → AO AB + C → AC + B AB + CD → AD + CB

Do you remember the five kinds of reactions? Most of these reactions involve the transfer of electrons from one atom to another.

Do you remember what makes a “happy atom”? Plus and minus charges balance Electron shells are exactly full.

Do you remember what makes a “happy atom”? Sodium is unhappy It has one more electron than will fit in its second shell Chlorine is unhappy It is missing one electron from its third shell.

Do you remember what makes a “happy atom”? Sodium gives its extra electron to chlorine They are still unhappy. Why? Sodium has a positive charge Chloride has a negative charge.

Do you remember what makes a “happy atom”? But if they stay attached to one another, they can make each other happy. In an ionic bond, the total charges balance out.

Do you remember what makes a “happy atom”? Na Cl

Do you remember what makes a “happy atom”? Na Cl

Do you remember what makes a “happy atom”? Na Cl

Do you remember what makes a “happy atom”? Na Cl

Do you remember what makes a “happy atom”? NaCl

Do you remember what makes a “happy atom”? NaCl

Do you remember what makes a “happy atom”? 2Na + Cl 2 → 2NaCl

Redox A reaction in which electrons are transferred from one atom to another is called an oxidation-reduction reaction, or “redox” for short.

Redox Originally, the word “oxidation” referred to reactions with oxygen. In combustion reactions, oxygen steals electrons from other atoms.

Redox Today, “oxidation” refers to any kind of atom stealing electrons from another.

Redox

Ger…

Redox Ger… Leo says “Ger”

Redox Ger… LEOGERLEOGER

Redox Ger… Loss of Electrons is Oxidation G E R

Redox Ger… Loss of Electrons is Oxidation Gain of Electrons is Reduction

Oxidation Number The oxidation number of an atom in an ionic compound is the number of electrons lost or gained when it forms an ion.

Oxidation Number Ca + Br 2 → CaBr 2

Oxidation Number Ca + Br 2 → CaBr 2 Ca + Br 2 → Ca Br -

Oxidation Number Ca + Br 2 → Ca Br -

Oxidation Number Ca + Br 2 → Ca Br - Ca 2+ charge = 2+ Br - charge = 1-

Oxidation Number Ca + Br 2 → Ca Br - Ca 2+ charge = +2 oxidation number = +2 Br - charge = -1 oxidation number = -1

Oxidation Number Ca + Br 2 → Ca Br - Calcium is oxidized by bromine.

Oxidation Number Ca + Br 2 → Ca Br - Calcium is oxidized by bromine. Bromine is reduced by calcium.

Oxidation Number Ca + Br 2 → Ca Br - Calcium is oxidized by bromine. Bromine is reduced by calcium. An oxidizing agent takes electrons.

Oxidation Number Ca + Br 2 → Ca Br - Calcium is oxidized by bromine. Bromine is reduced by calcium. An oxidizing agent takes electrons. A reducing agent gives electrons.

Oxidation Number Ca + Br 2 → Ca Br - Calcium is oxidized by bromine. Bromine is reduced by calcium. An oxidizing agent takes electrons. A reducing agent gives electrons. (LEO says GER)

Oxidation Number Covalent bonds can also involve redox reactions if the bonds are polar.

Homework Read pages Answer questions 1-3 on page 640