Chemical Bonding

• Chemical bonding includes ionic bonding, metallic bonding, covalent bonding and coordinate (dative covalent) bonding.
• The shapes of simple molecules and bond angles can be determined through chemical bonding.
• Bond polarities and polarity of molecules can be determined through chemical bonding.
• Intermolecular forces, including hydrogen bonding, can be studied through chemical bonding.
• Bond energies and bond lengths can be determined through chemical bonding.
• The lattice structure of solids can be understood through chemical bonding.
• Bonding and physical properties can be understood through chemical bonding.
• In ionic bonding, each ion attracts ions of opposite charge in all directions.
• Ionic bonds are formed as a result of electron transfer from the valence shell of one atom (that prefers to lose electrons, usually metals) to the valence shell of another (that prefers to gain electrons, usually non-metals).
• The ions produced in ionic bonds have a stable, complete octet structure of electrons (i.e. ns 2 np 6) where n = principal quantum number.
• Examples of compounds which contain ionic bonds include NaCl, MgO, CaO and MgF2.
• Ionic bonds are strong bonds.
• Ionic bonds are electrostatic forces of attraction between oppositely charged ions.
• Dot-and-cross diagrams can be used to illustrate electron(s) transfer during the formation of ionic compounds.
• VSEPR Theory Part 2: Trigonal Bipyramidal Family helps visualise the shapes on Page 27.
• VSEPR theory helps visualise the shapes on Page 26.
• Deduce the molecular geometry / shape of the species using Table 1 (Page 26).
• Chemical Bonding (I) 202 3 Semester 1 Page 3 - 26 + N H H H H H n Table 1: Shapes of Molecules / Polyatomic Ions.
• Lone pairs of electrons are closer to the nucleus than bond pairs of electrons.
• Water can never be a straight molecule because of the 2 lone pairs of electrons.
• Lone pairs of electrons would tend to push away neighbouring bond pairs of electrons, forcing bond pairs of electrons closer together.
• Bond angles in ammonia and water are smaller than those in methane due to the presence of lone pairs of electrons.
• The number of electron pairs, basic arrangement (of e − pairs), bond pairs, and lone pairs affect the shape of a molecule.
• Decreasing the bond angle between bond pairs of electrons is a result of the repulsion of lone pairs of electrons.
• VSEPR Theory Part 3: Octahedral Family helps visualise the shapes on Page 27.
• Bond pairs of electrons are localised between two nuclei while lone pairs of electrons are not.
• The atoms, molecules or ions of a crystalline solid are highly ordered in a regular 3-dimensional arrangement that repeat over and over again in all directions.
• Examples of crystalline solids include sodium chloride, diamond, iodine, ice and copper.
• Lattices of crystalline solids may be classified into four main types: Giant ionic lattice (e.g. sodium chloride), Giant molecular lattice (e.g. diamond, graphite and silicon dioxide), Simple molecular lattice (e.g. iodine and ice), and Giant metallic lattice (e.g. copper).
• The physical properties of a compound are a consequence of its structure and bonding.
• Al2Cl6 (dimer of AlCl3) forms a dative covalent bond when a vacant 2s orbital of aluminum (Al) accepts a pair of electrons from chlorine of Al2Cl6 to form a dative covalent bond.
• Each type of bond is associated with a quantity of energy, known as Bond Energy, which gives an indication of the strength of a covalent bond.
• Bond length is the distance between the nuclei of the atoms in a covalent bond.
• Bond polarity is the ability of a bond to exist as a dipole.
• H3O+ forms a dative covalent bond with Oxygen when a vacant 1s orbital of proton (H+) accepts a pair of electrons from oxygen of H3O+ to form a dative covalent bond.
• Bond Energy is the energy absorbed when a bond is broken and the energy released when a bond is formed.
• Two conditions for dative covalent bonding to occur: one atom/molecule has a lone pair of electrons, the other has a vacant low-lying orbital to accept the pair of electrons.
• Bond dissociation energy (ΔH) is the energy required to break one mole of a covalent bond, causing the bond to dissociate into its gaseous atoms.
• Coordinate (dative covalent) bonding involves the formation of a bond pair of electrons, a lone pair of electrons, and a dimer.
• Bond Energy gives an indication of the strength of a covalent bond.