JPJC 2026 Chemical Bonding Annotated Lecture Notes

2026 JPJC JC1 H2 Chemistry (9476) 1 Topic 3: Chemical Bonding Jurong Pioneer Junior College 2026 JC2 H2 Chemistry (9476) Physical Chemistry Teachers’ version Topic 3: Chemical Bonding Assessment Objectives Candidates 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 Al2Cl6 molecule (c) describe covalent bonding in terms of orbital overlap (limited to s and p orbitals only), giving  and  bonds (d) explain the shapes of, and bond angles in, molecules such as BF 3 (trigonal planar); CO 2 (linear); CH4 (tetrahedral); NH 3 (trigonal pyramidal); H 2O (bent); SF6 (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 a 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

2026 JPJC JC1 H2 Chemistry (9476) 2 Topic 3: Chemical Bonding Section Content LOs Page 1 Introduction 1.1 Why do atoms combine? (a) 3 1.2 What is a chemical bond? 3 1.3 Relative strength of chemical bonds 4 1.4 Some useful concepts 5 2 Covalent Bonding 2.1 Formation of covalent bond (a), (b), (c), (f), (j), (k) 6 2.2 Bond Polarity 12 2.3 Strength of covalent bond 13 3 Covalent Compounds 4 Giant Covalent Structure 4.1 Physical properties of giant covalent structure (l), (m), (n) 14 4.2 Diamond and graphite 15 4.2 Silicon and silicon dioxide 16 5 Simple Molecular Structure 5.1 Physical properties of simple molecular structure (d), (e), (g), (l) 17 5.2 Molecular shapes 18 5.3 Polarity of molecules 24 6 Intermolecular Forces of Attraction 6.1 Instantaneous dipole– induced dipole attraction (h), (i), (m), (n) 27 6.2 Permanent dipole – permanent dipole attraction 29 6.3 Hydrogen bonding 30 6.4 Solubility 33 7 Ionic Bonding 7.1 Formation of ions and ionic bond (a), (b), (l), (m), (n) 34 7.2 ‘Dot-and-cross’ diagram of ionic compounds 35 7.3 Giant Ionic Structure 36 7.4 Strength of ionic bond 36 7.5 Physical properties of ionic compounds 38 8 Metallic Bonding 8.1 Structure and bonding in metals (a), (m), (n) 40 8.2 Strength of metallic bond 41 8.3 Physical properties of metals 41

2026 JPJC JC1 H2 Chemistry (9476) 3 Topic 3: Chemical Bonding 1 INTRODUCTION As we examine the world around us, we find it to be composed mainly of elements, compounds and mixtures. Atoms tend to be bonded to one another as formation of bonds generally lower the overall energy of the system. The manner in which the atoms are bonded together has a profound effect on the chemical and physical properties of these substances. For example, graphite is soft and slippery while diamond is the hardest substance known. Such differences in physical properties are best explained by the bonding within these substances. 1.1 Why do atoms combine? Atoms combine to achieve noble gas outermost shell electronic configuration, i.e. duplet or octet structure. • Octet rule: Atoms / ions with 8 electrons in the valence shell are found to be stable (i.e. ns2 np6 valence shell electronic configuration). • Duplet rule: Similar stability is found in atoms / ions with 1s2 electronic configuration e.g. H, He, Li+ Electron rearrangement occurs in two ways: 1) Transfer of electrons from an atom to another atom 2) Sharing of electrons between two or more atoms Electron rearrangement results in the formation of chemical bonds. Note that it is only valence electrons that are involved in bonding. 1.2 What is a Chemical Bond? A chemical bond is the electrostatic attraction between a positively charged species and a negatively charged species. There are 3 general types of chemical bonds. Positive charge Negative charge Type of chemical bond Electrostatic attraction between metal cations and delocalised valence electrons Metallic bond cations anions Ionic bond nuclei of two atoms the bonding electrons shared between them Covalent bond Driving force to form chemical bonds is to lower the overall energy of the system. Since bond formation is exothermic, heat is given off when chemical bonds are formed. Type of attraction Electrostatic attraction between molecules Intermolecular forces *Understand the different types of bonding and relate the bonding to the physical properties of the substance. forms covalent bonds forms ions which then forms ionic bonds between cation and anion

2026 JPJC JC1 H2 Chemistry (9476) 4 Topic 3: Chemical Bonding 1.3 Relative strength of chemical bonds Type of bonds Strength of bonds energy / kJ mol-1 Ionic bond strong 100 – 450 Covalent bond 100 – 550 Metallic bond 50 – 600 Hydrogen bonding weak 13 – 30 Permanent dipole – dipole attraction 5 – 12 Instantaneous dipole – induced dipole < 4 IMF between molecules that contain H directly bonded to F, O or N atoms (highly electronegative atoms) Eg: HF, NH3, H2O, CH3CH2OH, CH3COOH, CH3CONH2 Figure 1.1 Overview of Structure and Bonding CHEMICAL BONDING Giant Metallic Structure METALLIC BONDING Giant Ionic Structure IONIC BONDING Hydrogen Bonding Simple Molecular/ Covalent Structure Limited examples: graphite, diamond, silicon, SiO2 Giant Molecular/ Covalent Structure contains simple molecules which are held by COVALENT BONDING Permanent dipole - permanent dipole attraction between polar molecules Eg: HCl, CHCl3, HCHO, CH3COCH3, CH3OCH3 between non-polar molecules or noble gas atoms Eg: H2, Cl2, Br2, CO2, CH4, CCl4, He, Ne, Ar Instantaneous dipole - induced dipole attraction INTERMOLECULAR FORCES OF ATTRACTION

2026 JPJC JC1 H2 Chemistry (9476) 5 Topic 3: Chemical Bonding 1.4 Some Useful Concepts (a) Metals and Non-metals