Transcript Slide 1
CHEM 120 WEEK 12 LECTURES (INORGANIC WEEK 3) Dr. MD BALA Intramolecular Bonding The bonding between molecules or atoms in the solid state Ionic bonding e.g. sodium chloride Covalent bonding e.g. Graphite or diamond Metallic bonding e.g. copper/gold etc. Van der Waals bonding e.g. iodine or benzene Hydrogen bonding e.g. water and alcohols IONIC BONDING Ions stack together in regular crystalline structures. Typically ionic solids. Have high melting and boiling points They are brittle. They form electrolyte solutions if they dissolve in water. Ionic Solids • The attractive force between a pair of oppositely charged ions increases with increased charge on the ions and with decrease in ionic sizes requires less energy to break up Na+ = 99 pm requires more energy to break up COVALENT BONDING Electron sharing Complete their octets by sharing electron pairs F F e.g. Consider F2 The electronic configuration of F is 1s22s22p5 F F These are combined to form F2. Metallic bonding It is a special case: • The electrons are considered to be “delocalized” • This gives rise to their properties such as malleability or ductility. • Good thermal and electrical conductors Electrostatic forces and the reason ionic compounds crack Electrical conductance and ion mobility Solid ionic compound Molten ionic compound Ionic compound dissolved in water van der Waals - Due to instantaneous dipoles non-conducting species Bond Polarity • Covalent bonding between unlike atoms results in unequal sharing of the electrons – One end has larger electron density than other • The result is bond polarity – End with larger e- density gets partial - charge – End that is e- deficient gets partial + charge H ••F Dipole Moment Allotropy and Polymorphism Allotropy: e.gs. of elements and their allotropes Polymorphism: Bonding in other elements and their chemistries Sulfur • Rhombic and monoclinic are different allotropes of sulfur (same elements but different structural or molecular units) Phosphorous Linear molecule with triple bond sp hybridized Compounds of oxygen (oxides) Acidity increases left to right (metals form basic ionic oxides) (metalloids form amphoteric oxides) (non-metals form acidic covalent oxides) Acids and Bases • Arrhenius definition: - An acid provides H+ ions (ionizable hydrogen) and a base produces OH- ions in an aqueous solution • Bronsted-Lowry: - An acid is a proton donor and a base is a proton acceptor • Lewis acids and bases: - An acid is a species that is an e- pair acceptor and a base is an e- pair donor. (base anhydride) Anhydride means “without water”. A “base without water” becomes a basic solutione when it reacts with water: CaO (s) + H2O base oxide Ca2+ (aq) + 2OH- (aq) calcium hydroxide The oxide ion is protonated to produce the hydroxide: O2- + H2O 2OH- (aq) (100%) A basic oxide reacts with acids to produce water CaO (s) + 2H+ (aq) Ca2+ (aq) + H2O (l) Oxoacids contain H and O and one other nonmetal Sulfurous acid Sulfuric acid base acid acid base tetra(hydroxo)aluminate(III) ion Exercise 1. Write a balanced equation for Zn(OH)2 with: a) an acid b) a base 2. Does the following species act as an acid, a base or an amphoteric species? a) PO43b) CH3NH3+ = CH3NüH2 + H+ Oxoacids Obtained from the dissolution of acidic oxides in water e.g. CO2 + H2O = H2CO3(aq) What are some Oxoacids? What are polyprotic acids? • They are acids with more than one ionizable H atom per molecule e.g. H3PO4 phosphoric acid (3 ionizable H atoms triprotic H2SO4 sulfuric acid diprotic H2SO3 sulfurous acid ’’ H2CO3 carbonic acid ’’ Halogens as oxoacids hypochlorite chlorite chlorate perchlorate especially E0 = +1.61 V H O Cl - the hydrogen in HOCl is attracted to the lone pair on oxygen atom in water - water accepts a proton base - HOCl donates a proton acid Exercise: a) What is the oxidation number of Cl in HOCl? b) What is the oxidation number of Cl in OCl-? c) What is the oxidation number of Cl in HClO4? Cl Strengths of oxoacids • How great is the pull of electrons away from the O-H bond? Affected by: 1. The electronegativity of the central atom 2. The no. of terminal O atoms in the acid molecule H O Cl H O Br ENCl = 3.0 ENBr = 2.8 Ka = 2.9 x 10-8 Ka =2.1 x 10-9 Which acid is stronger, H2SO4 or H2SO3? O O H O S O H H O S O H O Ka1a1==101033 -2 1.3xx 10 10-2 Ka1a1==1.3 Exercise Which acid is stronger? H O Cl O O H O I O O Nitrogen Nitrogen has oxidation nos. from -3 to +5 The most industrially useful states are: -3 for ammonia NH3 0 molecular nitrogen N2 +5 for nitric acid HNO3 Physical description: NO is colourless, paramagnetic (1 unpaired e-) and toxic Generation of NO: Prepared by the action of Cu(II) salts on nitric acid (HNO3): colourless nitrite(III ) colourless colourless