1Gram Equivalent WeightGram Equivalent WeightGram equivalent weight = gram atomic Gram equivalent weight = gram atomic weight or gram molecular weight divided weight or gram molecular weight divided by valenceby valenceFor acids and bases:For acids and bases:Gram equivalent weight = gram molecular Gram equivalent weight = gram molecular weight divided by the number of hydrogen weight divided by the number of hydrogen ion or hydroxyl ion groups when the acid ion or hydroxyl ion groups when the acid or base is dissociated in fluidor base is dissociated in fluidGram Equivalent Weight for CaGram Equivalent Weight for Ca2+2+Atomic weight calcium = 40.08 g/molAtomic weight calcium = 40.08 g/molValence = +2Valence = +2Gram equivalent weight = 40.08 (g/mol)/2 Gram equivalent weight = 40.08 (g/mol)/2 = 20.04 equivalents (= 20.04 equivalents (eqeq))For AcidsFor AcidsHH22SOSO44it is it is ½½the molecular weight the molecular weight because 2 H will dissociate in fluidbecause 2 H will dissociate in fluid½½molecular weight = 49.04 molecular weight = 49.04 eqeqHH33POPO44it is 1/3 the molecular weight it is 1/3 the molecular weight because 3 H will dissociate in fluidbecause 3 H will dissociate in fluid1/3 molecular weight = 32.67 1/3 molecular weight = 32.67 eqeqPeriodic LawPeriodic LawChemical and Physical properties of Chemical and Physical properties of elements are similar with increasing elements are similar with increasing atomic numberatomic numberElements in Groups have similar valences Elements in Groups have similar valences because they have similar electronic because they have similar electronic structuresstructuresThis leads to similar physical and chemical This leads to similar physical and chemical properties within groupsproperties within groups2Two GroupsTwo GroupsElectron Donors Electron Donors ––generally left side of generally left side of periodic table periodic table --metalsmetalsElectron Acceptors Electron Acceptors ––generally right side of generally right side of periodic table periodic table ––nonmetalsnonmetalsTransition elements Transition elements ––vary depending on how vary depending on how close to filling outer orbitalclose to filling outer orbitalComplete transfer of electrons results in:Complete transfer of electrons results in:+ charge if electron is lost + charge if electron is lost ––cationcation--charge if electron is gained charge if electron is gained --anionanionIonic Bonds Ionic Bonds ––most common form of most common form of bonding incorporating metals + nonmetalsbonding incorporating metals + nonmetalsCovalent Bonding Covalent Bonding ––elements of similar elements of similar metallic or nonmetallic character tend to metallic or nonmetallic character tend to share electronsshare electronsElectrons may not be shared equallyElectrons may not be shared equally••Result is net charge on the molecule (ionic Result is net charge on the molecule (ionic character for the molecule)character for the molecule)In ionic bonding, transfer of electrons is In ionic bonding, transfer of electrons is seldom complete (these molecules have seldom complete (these molecules have some covalent character)some covalent character)True covalent examples are: HTrue covalent examples are: H22, O, O22, N, N22Electron Donor or AcceptorElectron Donor or AcceptorQuantificationQuantificationFirst Ionization Potential: energy required First Ionization Potential: energy required to remove one electron from neutral atomto remove one electron from neutral atomIndicator of reactivity of an elementIndicator of reactivity of an elementMetallic character of elements decreases with Metallic character of elements decreases with increasing atomic numberincreasing atomic number3Electron Donor or AcceptorElectron Donor or AcceptorQuantificationQuantificationElectronegativityElectronegativity: measure of the ability of : measure of the ability of an atom in a molecule to attract electrons an atom in a molecule to attract electrons to itself.to itself.Dimensionless number calculated from known Dimensionless number calculated from known strengths of bondsstrengths of bondsMeasure of the ionic character of covalent Measure of the ionic character of covalent bondsbonds••Low electronegative atoms >>> electron donorsLow electronegative atoms >>> electron donors••High electronegative atoms >>> electron acceptorsHigh electronegative atoms >>> electron acceptorsElements with similar Elements with similar electronegativitieselectronegativitiesform covalent bonds with little ionic form covalent bonds with little ionic charactercharacterElements with difference in Elements with difference in electronegativitieselectronegativitiesform ionic bonds form ionic bonds proportional to the differenceproportional to the differenceBonding and DissociationBonding and DissociationCaCOCaCO33>>>>>>>>>> Ca>>>>>>>>>> Ca2+2++ CO+ CO3322--Bond between the calcium and carbonate Bond between the calcium and carbonate is largely ionicis largely ionicBond between carbon and oxygen is Bond between carbon and oxygen is largely covalentlargely covalentPut water molecule and hydration on the Put water molecule and hydration on the boardboardIonic CrystalsIonic CrystalsIonic crystals form in regular patterns based on Ionic crystals form in regular patterns based on closest packing of the ions and electrical closest packing of the ions and electrical neutrality of the crystalneutrality of the crystalClosest packing results because the electrostatic Closest packing results because the electrostatic bond (F) increases with decreasing distance (r) bond (F) increases with decreasing distance (r) between between cationscationsand anionsand anionsF = (eF = (e11ee22)/r)/r22F = electrostatic bondF = electrostatic bondee11and eand e22= charges on the ions= charges on the ionsCrystals are electrically neutral including after Crystals are electrically neutral including after substitutions occur in the crystal latticesubstitutions occur in the crystal lattice4Ratio of Ratio of cationscationsto anions (to anions (RcRc/Ra)/Ra)Geometry of ions is described by Geometry of ions is described by coordination numbercoordination