Oxidation-Reduction Reactions

Metals donate or lose electrons when they become ions. + 2 Metals donate or lose electrons when they become ions. Beryllium This gives metals a positive charge. Positively charged ions are called cations. + 1 When elements lose electrons and increase their charge, we say that they have been oxidized. Sodium

Nonmetals gain or accept electrons when they become ions. - 2 Nonmetals gain or accept electrons when they become ions. This gives nonmetals a negative charge. Negatively charged ions are called anions. Oxygen - 1 When elements gain electrons and lower their charge, we say that they have been reduced. Chlorine

Oxidation and reduction never happen alone Oxidation and reduction never happen alone. In order for an element to donate electrons, there must be an element to accept those electrons. +1 -1 sodium sodium chloride chlorine

Redox Reactions Oxidation-reduction reactions (often called redox reactions) are very common. Any time electrons are passed from one element to another, a redox reaction has taken place.

Identifying Oxidation and Reduction In order to easily identify the processes of oxidation and reduction, we write our equations using half reactions. These allow us to focus on what happened to a single element within a reaction. F2 + 2e-  2F- H2  2H+ + 2e-

Electrons are accepted/gained Electrons are donated/lost Reduction Oxidation F2 + 2e-  2F- H2  2H+ + 2e- Electrons are accepted/gained Electrons are donated/lost

For each of the half reactions on your notes, determine whether it represents oxidation or reduction.

Types of Redox Reactions This is known as a synthesis reaction. The diagram represents a reaction where two separate substances have joined together to create a single substance. This is usually accompanied by the oxidation and reduction of the substances. This is known as a synthesis reaction.

Types of Redox Reactions This is known as a decomposition reaction. This diagram represents a reaction where a single substance breaks apart into several smaller substances. This type of reaction is also usually accompanied by the oxidation and reduction of the substances. This is known as a decomposition reaction.

For each of the reactions on your notes, determine if the reaction is a synthesis or decomposition reaction.

CH4 (g) + 2O2 (g) → 2H2O(g) + CO2 (g) Types of Redox Reactions CH4 (g) + 2O2 (g) → 2H2O(g) + CO2 (g) Another type of reaction you should be able to recognize is the burning of a substance in the presence of oxygen. This produces water and carbon dioxide and always involves the oxidation and reduction of substances. This is known as a combustion reaction.

Chemical Properties of Metals The relative reactivity of metals is listed on in the activity series. Metals at the top of the list can replace metals below them inside of chemical compounds. Notice that hydrogen is the only nonmetal on the list. This is because of its unique properties. Metals at the top of the series, like sodium, replace hydrogen in water violently.

Zn + CuCl2  Cu + ZnCl2 Types of Redox Reactions A final type of reaction you will need to recognize involves one metal replacing another according to their reactivity. This always involves the oxidation and reduction of the metals. This is known as a single-replacement reaction.

Mg + CoCl2  Co + MgCl2 Ni + CaBr2  Ca + NiBr2 You can predict whether a reaction will occur or not using the activity series. In order for a reaction to occur, the metal that is doing the replacing must be higher on the activity series. If it is not, the reaction will not occur. Mg + CoCl2  Co + MgCl2 Magnesium is above cobalt, so this reaction will happen. Ni + CaBr2  Ca + NiBr2 Nickel is not above calcium, so this reaction will NOT happen.

Decide if each reaction will happen (YES) or will not happen (NO) based on the activity series.