Oxidation States The oxidation state or oxidation number of an element in a simple binary meaning 2 ionic compound is the number of e gained or lost by an atom of that element when it forms the compound NaCl Na ClMgBr2 Mg 2 BrThe most EN atom in a cpd is assigned a neg oxidation state while the less EN atom lose e and have pos oxidation states Usually the element with the pos oxidation state is written first except NH3 and hydrocarbons CH4 because of history H is 1 but written last Oxidation Numbers Guidelines for assigning oxidation numbers 1 The oxidation number of any free uncombined element is zero Such as H2 Na Cl2 Fe 2 The oxidation number of an element in a simple monatomic ion is the charge on the ion Na Mg2 3 In the formula for any compound the sum of the oxidation numbers of all elements in the compound is zero 4 In a polyatomic ion the sum of the oxidation numbers of the constituent elements is equal to the charge on the ion 2 Oxidation Numbers 5 Fluorine has an oxidation number of 1 in its compounds 6 Hydrogen H has an oxidation number of 1 unless it is combined with metals where it has the oxidation number 1 Examples LiH Li H BaH2 Ba 2 H7 Oxygen usually has the oxidation number 2 Exceptions In peroxides O has oxidation number of 1 Examples H2O2 CaO2 Na2O2 In OF2 O has oxidation number of 2 3 Oxidation Numbers 8 Use the periodic table to help with assigning oxidation numbers of other elements a IA metals have oxidation numbers of 1 b IIA metals have oxidation numbers of 2 c IIIA metals have oxidation numbers of 3 There are a few rare exceptions d VA elements have oxidation numbers of 3 in binary compounds with H metals or NH4 e VIA elements below O have oxidation numbers of 2 in binary compounds with H metals or NH4 Summary in Table 5 4 4 Oxidation Numbers Assign oxidation numbers to each element in the following compounds K 0 1 4 2 1 K2Sn OH 6 2 6 4 1 7 2 1 5 2 HClO4 NaNO3 1 8 7 1 6 5 5 3 2 5 2 NO2NO3 4 3 6 5 4 3 1 charge 6 5 1 charge 6 2 SO42SO32 8 6 8 6 2 charge Ag O2 Oxidation Numbers Clicker Q Oxidation for Au 0 Clicker Q 1 7 2 Oxidation for Mn in KMnO4 7 1 7 8 Clicker Q 1 3 2 Oxidation for N in HNO2 1 4 1 4 3 7 Periodic Trends It is important that you understand and know the periodic trends described in the previous sections They will be used extensively in Chapter 7 to understand and predict bonding patterns 8 Hydrogen and the Hydrides H2 discovered by Englishman Henry Cavendish n 1799 Hydrogen means water former Colorless odorless tasteless gas with the lowest MW and d of any known substance H2 very flammable Hindenburg airship disaster in 1937 Combustion is the highly exothermic combination of a substance with O2 usually with a flame Oxygen and the Oxides O2 was discovered by the Englishman Joseph Priestley in 1774 Oxygen means acid former Oxygen is an extremely reactive element O2 reacts with most metals to produce normal oxides having an oxidation number of 2 10 Combustion Reactions Combustion reactions are exothermic redox reactions Some of them are extremely exothermic One example of extremely exothermic reactions is the combustion of hydrocarbons Examples are butane and pentane combustion 2 C4H10 g 13 O2 g 8 CO2 g 10 H2O g C5H12 g 8 O2 g 5 CO2 g 6 H2O g 11 Fossil Fuel Contaminants When fossil fuels are burned they frequently have contaminants in them Sulfur contaminants in coal are a major source of air pollution Nitrogen from air can also be a source of significant air pollution This combustion reaction occurs in a car s cylinders during combustion of gasoline NO2 is the haze that we call smog N2 g O2 g 2 NO g Causes a brown haze in air 2 NO g O2 g 2 NO2 g NO2 is also an acid anhydride It reacts with water to form acid rain and unfortunately the NO is recycled to form more acid rain 12 Chapter 6 Some types of chemical reactions For Ch 6 end of chapter HW problems 3 5 6 8 9 12 14 16 18 19 21 22 27 29 3040 45 46 50 53 56 61 63 64 66 78 90 92 94 95 129 130 Aqueous Solutions An Introduction of the Earth s surface is covered with H2O Pure H2O does not conduct electricity 1 Electrolytes and Extent of Ionization Electrolytes are substances whose aqueous solutions conduct electric current Strong electrolytes are substances that conduct electricity well in dilute solution Weak electrolytes conduct electricity poorly in dilute aq solution 14 Nonelectrolytes do not conduct electricity Electric current is carried thru aq sol by the movement of ions The strength of an electrolyte depends on the of ions in solution and also on the charges on these ions Read green problem solving tip Larger anions with low neg charges almost always give soluble salts 3 major classes of solutes are strong electrolytes 1 Strong acids 2 Strong bases 3 Most soluble salts These cpds are completely or nearly completely ionized or dissociated in dilute aq solutions so they are strong electrolytes An acid can be defined as a substance that produces H in aq solution A base is a substance that produces OH ions in aq solution A salt is a cpd that contains a cation other than H and an anion other than OH or O2 Strong and weak acids Strong acids ionize separate into H and stable anions completely or nearly completely in dilute aq solutions NEED to memorize these 1 HCl hydrochloric acid 2 HBr hydrobromic acid 3 HI hydroiodic acid 4 HNO3 nitric acid 5 H2SO4 sulfuric acid 6 HClO3 chloric acid 7 HClO4 perchloric acid Weak acids ionize only slightly usually less than 5 in dilute aq solution so that s why they are weak less H 1 HF hydrofluoric acid 2 CH3COOH acetic acid vinegar 3 HCN hydrocyanic acid 4 HNO2 nitrous acid 5 H2CO3 carbonic acid soda water 6 H2SO3 sulfurous acid 7 H3PO4 phosphoric acid 8 COOH 2oxalic acid Strong acid 100 HNO 3 H 2 O H 3O aq NO 3 aq or H 2O HNO 3 H aq NO 3 aq Weak acid Reversible Reactions Reactions that occur in both directions are reversible reactions We use a double arrow to indicate that a reaction is reversible 7 CH 3COOH CH 3COO aq H aq Clicker Q Which one is a strong acid 1 HF 2 H2SO3 3 HCl 4 HCN Strong bases insoluble bases and weak bases Strong bases are soluble in water and are dissociated completely in dilute aq solution KNOW these Common Strong Bases 1 LiOH lithium hydroxide 2 NaOH sodium hydroxide 3 KOH potassium hydroxide 4 RbOH rubidium hydroxide 5 CsOHcesium hydroxide 6 Ca OH 2 …