EJC 2023 Chemical Bonding Lecture Notes (Student) (1)

E u n o i a J u n i o r C o l l e g e P a g e 1 2023 JC1 H2 CHEMISTRY (9729) CORE IDEA 2: STRUCTURE AND PROPERTIES TOPIC 3: CHEMICAL BONDING Name: ___________________________________________ Civics Group: _________ Students should be able to: (a) show understanding that all chemical bonds are electrostatic in nature and describe: (i) ionic bond as the electrostatic attraction between oppositely charged ions (ii) covalent bond as the electrostatic attraction between a shared pair of electrons and positively charged nuclei (iii) metallic bond as the electrostatic attraction between a lattice of positive ions and delocalised electrons (b) describe, including the use of ‘dot-and-cross’ diagrams, (i) ionic bonding as in sodium chloride and magnesium oxide (ii) covalent bonding as in hydrogen; oxygen; nitrogen ; chlorine; hydrogen chloride; carbon dioxide; methane; ethene (iii) co-ordinate (dative covalent) bonding, as in formation of the ammonium ion and in the A l2Cl6 molecule (c) describe covalent bonding in terms of orbital overlap (limited to s and p orbitals only), giving  and  bonds (see also Section 11.1) (d) explain the shapes of, and bond angles in, molecules such as BF3 (trigonal planar); CO2 (linear); CH4 (tetrahedral); NH 3 (trigonal pyramidal); H 2O (bent); SF 6 (octahedral) by using the Valence Shell Electron Pair Repulsion theory (e) predict the shapes of, and bond angles in, molecules analogous to those specified in (d) (f) explain and deduce bond polarity using the concept of electronegativity [quantitative treatment of electronegativity is not required] (g) deduce the polarity of a molecule using bond polarity and its molecular shape (analogous to those specified in (d)) (h) describe the following forces of attraction (electrostatic in nature): (i) intermolecular forces, based on permanent and induced dipoles, as in CHCl3(l), Br2(l) and the liquid noble gases (ii) hydrogen bonding, using ammonia and water as examples of molecules containing –NH and –OH groups (i) outline the importance of hydrogen bonding to the physical properties of substances, including ice and water (j) explain the terms bond energy and bond length for covalent bonds (k) compare the reactivities of covalent bonds in terms of bond energy, bond length and bond polarity (l) describe, in simple terms, the lattice structure of crystalline solid which is: (i) ionic, as in sodium chloride and magnesium oxide (ii) simple molecular, as in iodine (iii) giant molecular, as in graphite and diamond (iv) hydrogen-bonded, as in ice (v) metallic, as in copper [the concept of the ‘unit cell’ is not required] (m) describe, interpret and/or predict the effect of different types of structure and bonding on the physical properties of substances (n) suggest the type of structure and bonding present in a substance from given information

E u n o i a J u n i o r C o l l e g e P a g e 2 Lecture Contents 1 Covalent Bonding ................................ ................................ ................................ ................ 4 1.1 Covalent Bond Formation ................................ ................................ ................................ 4 1.2 The Overlap of Orbitals: Sigma Bonds and Pi Bonds ................................ ...................... 5 1.2.1 Sigma () Bonds ................................ ................................ ................................ .. 5 1.2.2 Pi () Bonds ................................ ................................ ................................ ......... 6 1.3 Types of Covalent Bonds ................................ ................................ ................................ 6 1.3.1 Multiple Bonding – Double and Triple Bond ................................ ......................... 6 1.3.2 Dative Bonding/Co-ordinate Bonding ................................ ................................ ... 7 1.4 Electronegativity ................................ ................................ ................................ .............. 8 1.5 Properties of Covalent Bonds ................................ ................................ .......................... 9 1.5.1 Bond Polarity ................................ ................................ ................................ ....... 9 1.5.2 Bond Strength ................................ ................................ ................................ .... 10 1.5.3 Bond Length ................................ ................................ ................................ ...... 11 1.6 Representing Covalent Bonds: Dot-And-Cross Diagrams................................ .............. 13 1.6.1 Dot-And-Cross for Molecules ................................ ................................ ............. 14 1.6.2 Dot-And-Cross Diagrams for Cations / Anions ................................ ................... 15 1.6.3 Dot-And-Cross Diagrams for Electron Deficient (with Incomplete Octet) Molecules 16 1.6.4 Dot-And-Cross Diagrams for Species with Odd Number (Unpaired) Valence Electrons ................................ ................................ ................................ ............ 17 1.6.5 Dot-And-Cross Diagrams for Expansion of Octet Structures .............................. 17 1.6.6 Dot-And-Cross Diagrams Showing Dative Covalent Bonds ................................ 18 2 Shape and Polarity ................................ ................................ ................................ ............. 20 2.1 The Valence Shell Electron Pair Repulsion (VSEPR) Theory ................................ ........ 20 2.2 Polarity of Molecules ................................ ................................ ................................ ..... 24 3 Intermolecular Forces of Attraction ................................ ................................ .................. 27 3.1 Instantaneous Dipole–Induced Dipole Interactions ................................ ........................ 27 3.2 Permanent Dipole–Permanent Dipole Interactions ................................ ........................ 30 3.3 Hydrogen Bonding................................ ................................ ................................ ......... 31 3.4 Comparing the Three Types of Intermolecular Forces of Attraction ............................... 32 4 Covalent Substances and Their Physical Properties ................................ ...................... 36 4.1 Simple Molecules ................................ ................................ ................................ .......... 36 4.2 Influence of Hydrogen Bonding on Physical Properties of Molecules ............................ 38 4.2.1 Unusually high boiling points of ammonia, water and hydrogen fluoride ............. 38 4.2.2 Anomalous relative molecular masses of organic acids (R–CO2H) .................... 39 4.2.3 High solubility of ammonia, alcohols (R–OH), organic acids and amines (R–NH2) in water ................................ ................................ ................................ .............. 39 4.2.4 Different physical properties of isomers ................................ ............................. 40 4.2.5 Higher density of water compared to ice ................................ ............................ 41 4.3 Giant Molecular Structures ................................ ................................ ............................ 42

E u n o i a J u n i o r C o l l e g e P a g e 3 5 Ionic Bonding ................................ ................................ ................................ ..................... 45 5.1 Formation of Ionic Bond ................................ ................................ ................................ 45 5.2 Factors affecting Ionic Bond Strength ................................ ................................ ...........