CHM 151 Cheat Sheet for CHM 152

CHM 151 Cheat Sheet for CHM 152 These are things that are vital to your understanding of CHM 152. You should know the following. Oxidation states (just a fancy name for charge) 1. Elements are all charge zero in their natural states which are: i. Gas: H2, N2, O2, F2, Cl2 and noble gases ii. Liquid: Hg and Br2 are the only liquids iii. Solid: everything else iv. Diatomic: H2, N2, O2, F2, Cl2, Br2 and I2 are the diatomic elements 2. Alkali metals are always charged +1 when in a compound. Their goal is to lose one electron, thus becoming +1 cations. 3. Alkaline Earth metals are always charged +2 when in a compound. Their goal is to lose two electrons, thus becoming +2 cations. 4. B column is usually charged +3 or -5 depending on what they are bonded to. They can lose 3 electrons becoming +3 OR gain 5 electrons becoming -5. Actually Al, Ga and In are always +3. 5. C column is usually charged +4 or -4 depending on what it is bonded to. They can lose 4 electrons becoming +4 OR gain 4 electrons becoming -4. (They can also be +2 or -2.) Example CH4 : C is -4 and H is +1. Example CO2 : C is +4 and O is -2. 6. N column is usually charged -3 in compounds but sometimes +5. They can lose 5 electrons becoming +5 OR gain 3 electrons becoming -3. Example NH3 N is -3 and H is +1. 7. Chalcogens are usually charged -2 in compounds (Oxygen is always charged -2 when in a compound except for peroxides like H2O2 where it is -1) unless they are bonded to something more electronegative than they are, in this case they can be +6 +4 or +2. Example sulfate ion. SO42- Here the total charge is -2 so S is +6, each O is -2 (there are 4 of them so that adds up to -8 for all four O's) so that adds up to -2 overall, which is why sulfate is an ion and not a molecule - it has an overall charge. 8. Halogens are usually charged -1 in compounds (F always is -1) unless they are bonded to something more electronegative than they are, in this case they can be +7 +5 or +3. Example IF7. Here F is -1 since it always is -1. That makes I +7. Note that IF5 and IF3 also exist. 9. Noble gases are stable and unreactive, they don't often have a charge - they are neutral atoms. 10. Transition metals have many charges, too many to predict. Exceptions are Zn and Cd which are always +2 and silver which is always +1. Re can be charged from +1 all the way up to +9!!! 11. H is usually +1. When H is bonded to a metal however, it can be -1. Example NaH where Na is +1 since it is always +1 so H must be -1. 12. Remember the atoms in a pure element have a charge of ZERO!!! Atoms don't have charges unless they are bonded to something else. Ions and Ionic Formulas – note an ionic formula must add up to zero total charge 1. Metals or cations are always first (NaCl not ClNa) 2. A few examples: a. magnesium phosphate = Mg3(PO4)2 (Mg is +2 so we need 3 of them, phosphate is -3 so 2 are needed) b. sodium sulfate = Na2SO4 (Na is +1 so we need 2 of them since sulfate is -2) c. calcium hydroxide = Ca(OH)2 (Ca is +2 and OH is -1 so we need 2 of them) 3. Polyatomic ions you should know: sulfate SO42- , phosphate PO43- , carbonate CO32- , hydroxide OH- , ammonium NH4+ , acetate CH3COO-1 , nitrate NO3- , bicarbonate HCO3- , monohydrogen phosphate HPO42- , dihydrogen phosphate H2PO4-1 4. Don’t show the charges in a compound (NaCl not Na+Cl-). Write the charges on scratch paper, but not in your chemical reactions or answers. We should not see charges above your compounds on your final answers. 5. Fluorine is F not Fl by the way. 6. If we say aluminum, we mean the element Al(s). If we say aluminum chloride, then we have Al3+ ions because it is an ionic compound or AlCl3(aq). Note that AlCl3(aq) really means one Al3+(aq) ion and 3 Cl- (aq) ions in water. There is no such thing as Al3+(s). Al is either a solid element with no charge, OR it is an ion with a +3 charge. 7. Dissolving in water. Soluble ionic compounds dissolve in water, which is NOT reacting with water. NaCl (s) some products is NOT Na+(aq) + Cl-(aq) is the correct way to show dissolving. NaCl (s) + H2O(l) correct since the salt is not reacting WITH water, it is just dissolving IN water. 8. When ionic compounds dissolve in water they break into separate ions. For example MgCl2 (aq) breaks into Notice the Cl- ions are NOT next to each other. This is 3 ions. The compound MgCl2 looks like because negative ions repel, so the Cl ions try to get far away from each other on opposite sides of the Mg2+ ion to which they are attracted. When we write MgCl2 we do not mean that chlorine, Cl2 is in it. We mean there are two totally separate Cl- ions in it. So when MgCl2(s) is put in water we get three ions: Cl- and Mg2+ and Cl- which is Mg2+(aq) and 2 Cl- (aq). So now you know that the 2 in 2 Cl- (aq) means two totally separated chloride ions floating around in water and not chlorine Cl2 which is a gaseous element. 9. There is no such thing as Cl2- ion. Read above. Chlorine is either a gas element with no charge Cl2(g) or it is Cl- (aq) ions. 10. What about when we put calcium hydroxide, Ca(OH)2 in water? It is soluble and makes 3 ions: One Ca2+ (aq) ion and two totally separate and distinct OH- ions. Again this compound looks like the one above but Ca2+ is in the middle of the two OH- ions. So there is no (OH)2- ion. The OH- ions were never touching, so they are not together making diatomic hydroxide ions. The formula Ca(OH)2 merely indicates there are two OH- ions in the chemical, but not how they are bonded. Nomenclature Review 1. Binary Ionic Compounds (ionic compounds with two elements) a. use the metal's name + the nonmetal's name + the suffix "ide" b. NaCl is sodium chloride, Li2O is lithium oxide, KBr is potassium bromide, MgI2 is magnesium iodide 2. Ionic compounds with polyatomic ions a. treat polyatomic ions as groups b. never change the name of the polyatomic ion c. NaOH is sodium hydroxide, Ca(NO3)2 is calcium nitrate, MgSO4 is magnesium sulfate d. ammonium sulfide is (NH4)2 S, calcium carbonate is CaCO3, magnesium phosphate is Mg3(PO4)2 3. Binary Covalent Compounds (covalent compounds with two elements) a. prefix + nonmetal + prefix + nonmetal + suffix "ide" b. prefixes are mono, di, tri, tetra, penta, hexa, hepta, octa c. if there is only one of the first nonmetal, don't use the mono prefix d. carbon tetraiodide is CI4, sulfur dioxide is SO2, N2H4 is dinitrogen tetrahydride 4. Transition metal compounds: name of transition metal, (charge in Roman numerals) + name of nonmetal + ide a. Fe2O3 - iron(III) oxide, CuS - copper(II) sulfide, FeSO4 - iron(II) sulfate, iron(II) phosphate - Fe3(PO4)2 Chemical Reactions C(aq) + D2+ (aq). The total charge of the reactants must be the same as the total charge of the products. Here the reactants are zero but the products are +2. So that means you created charge and solved the energy crisis! This reaction works: C(aq) + D2+ (aq). It works because both sides add up to +2. The charge is balanced. 2 A+ (aq) + B(aq) Remember when writing reactions, you must have all the correct formulas for the reactant(s) and product(s) first. Formulas depend on the charges of the elements and polyatomic ions involved. Once you have determined the formulas, you can NOT change them later - don't change the subscripts in the formulas. For example sodium and chlorine make NaCl. You cannot later while balancing change this to NaCl2. You can only add coefficients in front of the compounds to balance the reaction - like 2 NaCl. Formation rxn: reactants are elements in their natural state forming a product compound. Example: N2(g) + 3 H2(g) 2 NH3(g) Combustion rxn: hydrocarbon (molecule with only C and H) adding to oxygen producing water and CO2 Precipitation rxn: (a type of double replacement) when the cations swap anions and one product is NOT soluble Acid Base rxn: Typically where the H+ from an acid comes off and the base (often hydroxide ion) gains the H+ to make water. Single Displacement: typically when a solid metal element is put in solution and it trades places with the cation of a less active metal in solution. Note – two metals do NOT combine because positive ions repel. Example: 3 CoCl2(aq) + 2 Al(s) 2 AlCl3(aq) + 3 Co(s) You need to be able to write similar rxns on your own. Note the product is not ZnAl – the metals don’t combine because both want to get rid of electrons, not gain them. Also note that the cobalt product is a solid metal, not an ion, because we must balance charge! 1. You can not create charge during a reaction: (this is wrong) A (aq) + B(aq) 2. 3. 4. 5. 6. 7.