LU6 Student-Copy Ionic Bonding & Metallic Bond PDF

Made with Xodo PDF Reader and Editor MOLECULES AND MOLECULAR STRUCTURE LEARNING UNIT 6  Made with Xodo PDF Reader and Editor 6.1 IONIC BONDING 6.1.1 Bonding in ionic compound and giant ionic lattice...

Made with Xodo PDF Reader and Editor MOLECULES AND MOLECULAR STRUCTURE LEARNING UNIT 6  Made with Xodo PDF Reader and Editor 6.1 IONIC BONDING 6.1.1 Bonding in ionic compound and giant ionic lattices 6.1.2 Strength of ionic bond PRP1016 CHEMISTRY I | CENTRE FOR PRE-UNIVERSITY STUDIES 2 PERSONAL USED ONLY | NOT FOR SALE  Made with Xodo PDF Reader and Editor LEARNING OUTCOMES 3 By the end of this lecture, you should be able to: explain the formation of ionic bonds define lattice energy in ionic compound PRP1016 CHEMISTRY I | CENTRE FOR PRE-UNIVERSITY STUDIES PERSONAL USED ONLY | NOT FOR SALE  Made with Xodo PDF Reader and Editor Introduction on Chemical Bonding 4 Chemical bonding - forces that hold atoms together in molecules or compounds. The orientation of bonds will determine the shape of a molecule. When atoms combine, they can lose, gain or share electrons to attain an octet configuration. PRP1016 CHEMISTRY I | CENTRE FOR PRE-UNIVERSITY STUDIES PERSONAL USED ONLY | NOT FOR SALE  Made with Xodo PDF Reader and Editor Types of Chemical Bonding 5 Covalent Ionic Metallic Chemical bonding PRP1016 CHEMISTRY I | CENTRE FOR PRE-UNIVERSITY STUDIES PERSONAL USED ONLY | NOT FOR SALE  Made with Xodo PDF Reader and Editor Ionic Bonding 6 Ionic or electrovalent bonding is the electrostatic attractions that hold the oppositely charged ions together. Involve the transfer (lose/gain) of electron(s) from one atom to another to attain an octet configuration. Octet rule: Elements react in a way that results in valence shell containing eight electrons. PRP1016 CHEMISTRY I | CENTRE FOR PRE-UNIVERSITY STUDIES PERSONAL USED ONLY | NOT FOR SALE  Made with Xodo PDF Reader and Editor Ionic Bonding 7 Electron is given away Atom with spare electron Atom needs an electron to become stable Metal : Non-metal: - lose electron(s) - gain electron(s) - form cation(s) - form anion(s) PRP1016 CHEMISTRY I | CENTRE FOR PRE-UNIVERSITY STUDIES PERSONAL USED ONLY | NOT FOR SALE  Made with Xodo PDF Reader and Editor Bonding in Simple Ionic Compound 8 Formation of MgCl2 compound - ××. Cl [ ] × ×× × Cl × ×. Mg. ×× × ×. Cl - 2+ ×× + [Mg] [ ] ×× ×× × × × Cl × × ×× × ×× PRP1016 CHEMISTRY I | CENTRE FOR PRE-UNIVERSITY STUDIES PERSONAL USED ONLY | NOT FOR SALE  Made with Xodo PDF Reader and Editor Bonding in Giant Ionic Lattice 9 Giant ionic lattice - compound consist of endlessly repeating ions. In ionic lattices, each ion is bind by attractive forces, thus require higher energy to separate them. Lattice Energy - Energy released during formation of lattice solid of ionic compound from its gaseous ions. Li+ (g) + F- (g) → LiF (s) PRP1016 CHEMISTRY I | CENTRE FOR PRE-UNIVERSITY STUDIES PERSONAL USED ONLY | NOT FOR SALE  Made with Xodo PDF Reader and Editor Bonding in Giant Ionic Lattice 10 i. Lattice energy is affected by the ionic charge  The higher the charge, the stronger the attraction forces between the ions, the larger the lattice energy. Na+ F− Ca2+ O2− 231 pm 239 pm Lattice energy Lattice energy = −910 kJ mol−1 = −3414 kJ mol−1 PRP1016 CHEMISTRY I | CENTRE FOR PRE-UNIVERSITY STUDIES PERSONAL USED ONLY | NOT FOR SALE  Made with Xodo PDF Reader and Editor Bonding in Giant Ionic Lattice 11 Lattice energy ii. Lattice energy is affected (kJ mol−1) by the ionic size Na+ Cl− −787  The larger the size, the weaker the attraction forces between the ions, the smaller the lattice energy. Na+ Br− −751 −705 Na+ I− PRP1016 CHEMISTRY I | CENTRE FOR PRE-UNIVERSITY STUDIES PERSONAL USED ONLY | NOT FOR SALE  Made with Xodo PDF Reader and Editor Strength and Properties of Ionic 12 Compound High energy is required to break the strong ionic bonds Exist as crystalline solid at room temperature Conduct electricity in molten and aqueous but not in solid state High melting and high boiling points Soluble in water, but insoluble in non-polar solvent PRP1016 CHEMISTRY I | CENTRE FOR PRE-UNIVERSITY STUDIES PERSONAL USED ONLY | NOT FOR SALE  Made with Xodo PDF Reader and Editor 13 Exercise Which of the two compounds, potassium chloride and calcium chloride has higher lattice energy? Briefly explain. ANSWER: PRP1016 CHEMISTRY I | CENTRE FOR PRE-UNIVERSITY STUDIES PERSONAL USED ONLY | NOT FOR SALE  Made with Xodo PDF Reader and Editor 6.2 METALLIC BOND 6.2.1 Electron-sea model 6.2.2 Band theory – conductor, insulator and semiconductor PRP1016 CHEMISTRY I | CENTRE FOR PRE-UNIVERSITY STUDIES 14 PERSONAL USED ONLY | NOT FOR SALE  Made with Xodo PDF Reader and Editor LEARNING OUTCOMES 15 By the end of this lecture, you should be able to: explain the formation of metallic bond describe the Band Theory PRP1016 CHEMISTRY I | CENTRE FOR PRE-UNIVERSITY STUDIES PERSONAL USED ONLY | NOT FOR SALE  Made with Xodo PDF Reader and Editor Metallic Bond- Electron Sea Model 16 Metallic bonding is the force of attraction between the positive metal ions and the delocalised electrons...... + + + + + +. Free electrons from outer shells of.. + + + + + metal atoms. + + + + + + Metal ions PRP1016 CHEMISTRY I | CENTRE FOR PRE-UNIVERSITY STUDIES PERSONAL USED ONLY | NOT FOR SALE  Made with Xodo PDF Reader and Editor Properties of Metals 17 High melting and boiling temperatures due to strong metallic bonds between the atoms. Malleable and ductile. Can be deformed without breaking. Good conductor of heat and electricity in both the solid and liquid states due to delocalised mobile electrons. PRP1016 CHEMISTRY I | CENTRE FOR PRE-UNIVERSITY STUDIES PERSONAL USED ONLY | NOT FOR SALE  Made with Xodo PDF Reader and Editor Band Theory 18 When atomic orbitals overlap, molecular orbitals are formed. In a metal, the number of molecular orbitals produced is very large. The energy separations between these molecular orbitals are extremely small. This collection of very closely spaced molecular orbital energy levels is called an energy band. The molecular orbital theory for metal is called the band theory. PRP1016 CHEMISTRY I | CENTRE FOR PRE-UNIVERSITY STUDIES PERSONAL USED ONLY | NOT FOR SALE  Made with Xodo PDF Reader and Editor Band Theory 19 Two groups of energy levels. Lower energy level - Valence band contains the valence electrons Higher energy level - Conduction band contains the empty molecular orbitals. PRP1016 CHEMISTRY I | CENTRE FOR PRE-UNIVERSITY STUDIES PERSONAL USED ONLY | NOT FOR SALE  Made with Xodo PDF Reader and Editor Band Theory 20 Conduction band Valence- Conduction band Conduction band Conduction band Energy gap Half-full of electrons Full of electrons Valence band Energy Valence band Full of electrons (a)Metal (b) Insulator (c) Semiconductor PRP1016 CHEMISTRY I | CENTRE FOR PRE-UNIVERSITY STUDIES PERSONAL USED ONLY | NOT FOR SALE  Made with Xodo PDF Reader and Editor Band Theory 21 a) Metal There is no energy gap between the valence and Valence- conduction bands. Conduction band When an electrical potential is applied, the valence electrons Half-full of electrons can jump to the conduction Energy band and are free to move in the conduction band. Hence, metals are good conductor of (a) Metal electricity. Example: Copper PRP1016 CHEMISTRY I | CENTRE FOR PRE-UNIVERSITY STUDIES PERSONAL USED ONLY | NOT FOR SALE  Made with Xodo PDF Reader and Editor Band Theory 22 b) Insulator The energy gap between the Conduction band valence band and the conduction band is large. Conduction band Electrons in the valence band Energy gap cannot jump across into the conduction band. Hence, Valence band Energy insulator cannot conduct Full of electrons electricity. (b) Insulator Example: Diamond PRP1016 CHEMISTRY I | CENTRE FOR PRE-UNIVERSITY STUDIES PERSONAL USED ONLY | NOT FOR SALE  Made with Xodo PDF Reader and Editor Band Theory 23 c) Semiconductor However, the electrical conductivities are lower than metals Conduction band due to small number of electrons in the conduction band. Increasing the temperature of a Full of electrons Energy semiconductor increases its Valence band electrical conductivity. (c) Semiconductor Example of semiconductor: Silicon & Germanium PRP1016 CHEMISTRY I | CENTRE FOR PRE-UNIVERSITY STUDIES PERSONAL USED ONLY | NOT FOR SALE  Made with Xodo PDF Reader and Editor 24 Next Lecture PRP1016 CHEMISTRY I | CENTRE FOR PRE-UNIVERSITY STUDIES PERSONAL USED ONLY | NOT FOR SALE  Made with Xodo PDF Reader and Editor 6.3 COVALENT BOND AND COORDINATE BOND 6.3.1 Dot-cross diagram of the covalent bond 6.3.2 Multiple covalent bonds PRP1016 CHEMISTRY I | CENTRE FOR PRE-UNIVERSITY STUDIES 25 PERSONAL USED ONLY | NOT FOR SALE  Made with Xodo PDF Reader and Editor LEARNING OUTCOMES 26 By the end of this lecture, you should be able to: explain the formation of covalent bonds define simple molecular structure draw a Lewis electron-dot symbols of the covalent bond PRP1016 CHEMISTRY I | CENTRE FOR PRE-UNIVERSITY STUDIES PERSONAL USED ONLY | NOT FOR SALE  Made with Xodo PDF Reader and Editor Covalent Bonding 27 The covalent bond is formed when two electrons are shared between two atoms. The covalent compound is formed from combination of atoms of the same element or between the atoms of non-metals. H H H C H H C H H H PRP1016 CHEMISTRY I | CENTRE FOR PRE-UNIVERSITY STUDIES PERSONAL USED ONLY | NOT FOR SALE  Made with Xodo PDF Reader and Editor Covalent Bonding 28 When two non-metallic atoms come close together: There is an attraction between electrons (-ve) and the nuclei (+ve) of the atoms There are also repulsive forces between electrons (-ve) in both atoms and between nuclei (+ve) in both atoms These forces just balance when nuclei are at particular distance apart called the bond length Bond length PRP1016 CHEMISTRY I | CENTRE FOR PRE-UNIVERSITY STUDIES PERSONAL USED ONLY | NOT FOR SALE  Made with Xodo PDF Reader and Editor Covalent Bonding 29 Bonding pairs and Lone pairs in Covalent Bonding H F Lone pair electrons Hydrogen fluoride has 1 bonding pair and 3 lone pairs Bonding pair electrons PRP1016 CHEMISTRY I | CENTRE FOR PRE-UNIVERSITY STUDIES PERSONAL USED ONLY | NOT FOR SALE  Made with Xodo PDF Reader and Editor Lewis Electron-Dot Symbols of the 30 Covalent Bond Example 1: Methyl Chloride, CH3Cl H H H......... H C Cl ×.. H ×.C × Cl. H C.. Cl. × H H H Lewis Structure PRP1016 CHEMISTRY I | CENTRE FOR PRE-UNIVERSITY STUDIES PERSONAL USED ONLY | NOT FOR SALE  Made with Xodo PDF Reader and Editor Lewis Electron-Dot Symbols of the 31 Covalent Bond How to write a Lewis structure of NF3? 1. Determine the total number of valence electron available. Add up the valence electrons: Nitrogen (1 atom) = 5 e– Flourine (3 atoms) = 7 e– × 3 atoms = 21 e– Total is 26 valence electrons PRP1016 CHEMISTRY I | CENTRE FOR PRE-UNIVERSITY STUDIES PERSONAL USED ONLY | NOT FOR SALE  Made with Xodo PDF Reader and Editor Lewis Electron-Dot Symbols of the 32 Covalent Bond How to write a Lewis structure of NF3? 2. Place atom with the lowest electronegativity, EN in center. N has lower EN than F, so N will be the central atom and 3 atoms F are the side atoms. F F N F PRP1016 CHEMISTRY I | CENTRE FOR PRE-UNIVERSITY STUDIES PERSONAL USED ONLY | NOT FOR SALE  Made with Xodo PDF Reader and Editor Lewis Electron-Dot Symbols of the 33 Covalent Bond How to write a Lewis structure of NF3? 3. Draw a single bond from each surrounding atom to the central atom. F There must be at least single bond between bonded atoms. F N F Now, 6 electrons are distributed as bond pairs. PRP1016 CHEMISTRY I | CENTRE FOR PRE-UNIVERSITY STUDIES PERSONAL USED ONLY | NOT FOR SALE  Made with Xodo PDF Reader and Editor Lewis Electron-Dot Symbols of the 34 Covalent Bond How to write a Lewis structure of NF3?.. 4. Distribute the remaining electrons in F.... pairs, so that each side atom ends up with eight electrons )or (two for hydrogen.... atom)... F N.. F.... Now, 18 electrons are distributed as lone pairs. PRP1016 CHEMISTRY I | CENTRE FOR PRE-UNIVERSITY STUDIES PERSONAL USED ONLY | NOT FOR SALE  Made with Xodo PDF Reader and Editor Lewis Electron-Dot Symbols of the 35 Covalent Bond How to write a Lewis structure of NF3? 5. If any electrons remain, place them.. F.... around the central atom as lone pair (s) Make sure all atoms obey OCTET RULES...... F N.. F.... unless it is included in exception to octet.. rules. Now, 26 electrons are distributed as bond and lone pairs. PRP1016 CHEMISTRY I | CENTRE FOR PRE-UNIVERSITY STUDIES PERSONAL USED ONLY | NOT FOR SALE  Made with Xodo PDF Reader and Editor 36 Exercise Write the Lewis structure for CCl2F2, a compound that responsible for ozone depletion. ANSWER: PRP1016 CHEMISTRY I | CENTRE FOR PRE-UNIVERSITY STUDIES PERSONAL USED ONLY | NOT FOR SALE  Made with Xodo PDF Reader and Editor Exceptions to The Octet Rule 37 Expanded Incomplete Odd Typical for element in Molecules containing Free radicals contain the third period and aluminium, beryllium lone (unpaired) electron beyond that posses d and boron are normally orbitals electron deficient Total electrons of central Total electrons of central Total electrons of central atom is more than 8 atom is less than 8 atom is odd number electrons electrons SF6 AlCl3 ClO2 PCl5 BF3 NO SO42- BeCl2 NO2 PRP1016 CHEMISTRY I | CENTRE FOR PRE-UNIVERSITY STUDIES PERSONAL USED ONLY | NOT FOR SALE  Made with Xodo PDF Reader and Editor 38 Exercise State the exception of octet rule for the following covalent molecules: ANSWER: PRP1016 CHEMISTRY I | CENTRE FOR PRE-UNIVERSITY STUDIES PERSONAL USED ONLY | NOT FOR SALE  Made with Xodo PDF Reader and Editor Multiple Covalent Bonds 39 One electron pair being shared Single bond Hydrogen gas Two electron pairs being shared Double bond Oxygen gas Three electron pairs being shared Triple bond Nitrogen gas PRP1016 CHEMISTRY I | CENTRE FOR PRE-UNIVERSITY STUDIES PERSONAL USED ONLY | NOT FOR SALE  Made with Xodo PDF Reader and Editor 40 Exercise State how many bonding pair(s) and lone pair(s) in water molecule. O H H ANSWER: PRP1016 CHEMISTRY I | CENTRE FOR PRE-UNIVERSITY STUDIES PERSONAL USED ONLY | NOT FOR SALE  Made with Xodo PDF Reader and Editor 41 Next Lecture PRP1016 CHEMISTRY I | CENTRE FOR PRE-UNIVERSITY STUDIES PERSONAL USED ONLY | NOT FOR SALE  Made with Xodo PDF Reader and Editor 6.3 COVALENT BOND AND COORDINATE BOND 6.3.3 Coordinate bond 6.3.4 Resonance structure 6.3.5 Formal charge 6.3.6 Ionic to covalent – a continuum PRP1016 CHEMISTRY I | CENTRE FOR PRE-UNIVERSITY STUDIES 42 PERSONAL USED ONLY | NOT FOR SALE  Made with Xodo PDF Reader and Editor LEARNING OUTCOMES 43 By the end of this lecture, you should be able to: explain the formation of coordinate bonds explain the formation of resonance structure calculate formal charge of a Lewis structure PRP1016 CHEMISTRY I | CENTRE FOR PRE-UNIVERSITY STUDIES PERSONAL USED ONLY | NOT FOR SALE  Made with Xodo PDF Reader and Editor Coordinate Bond 44 Coordinate bond or dative covalent bond - a covalent bond in which both electrons come from the same atom. Example 1: Ammonium ion, NH4+ H H H + H N H+ H N H H N H H H H PRP1016 CHEMISTRY I | CENTRE FOR PRE-UNIVERSITY STUDIES PERSONAL USED ONLY | NOT FOR SALE  Made with Xodo PDF Reader and Editor Coordinate Bond 45 Example 2: Chemical bonding in Al2Cl6 As the AlCl3 gas is cooled, two AlCl3 molecules unite to form a dimers with molecular formula Al2Cl6, which held by coordinate bonds. A dimer is a molecule comprised of two identical molecules linked together. Cl Cl Cl Cl 2 Al Electron-pair Al Al acceptor Cl Cl Cl Cl Cl Electron-pair donor PRP1016 CHEMISTRY I | CENTRE FOR PRE-UNIVERSITY STUDIES PERSONAL USED ONLY | NOT FOR SALE  Made with Xodo PDF Reader and Editor Coordinate Bond 46 3+ Example 3: Chemical bonding in hydrated metal ion The water molecules clustering around Al ion and forms six coordinate bonds. Ions with water molecules attached are described as Al hydrated ions. Central metal Al have more than H 8 electron valence - Exceptions O H to the octet rule! PRP1016 CHEMISTRY I | CENTRE FOR PRE-UNIVERSITY STUDIES PERSONAL USED ONLY | NOT FOR SALE  Made with Xodo PDF Reader and Editor Resonance structure 47 Molecules can be represented by more than one reasonable Lewis structure that differ only in the location of π electrons Rules to remember to recognize resonance structures: Same relative placement of atoms but different locations of bonding and lone pair electrons You can only move electrons in π bonds or lone pairs (that are in p orbitals) The overall charge of the resonance structure must remain the same. The bond length remain unchanged. PRP1016 CHEMISTRY I | CENTRE FOR PRE-UNIVERSITY STUDIES PERSONAL USED ONLY | NOT FOR SALE  Made with Xodo PDF Reader and Editor Resonance structure 48 Two or more equivalent Lewis structures for a molecule. Example 1: Ozone, O3 Hybrid Resonance Structure Example 2: Nitrate ion, NO3− -.. -.. - O O O............ N N N O O O O O O PRP1016 CHEMISTRY I | CENTRE FOR PRE-UNIVERSITY STUDIES PERSONAL USED ONLY | NOT FOR SALE  Made with Xodo PDF Reader and Editor Formal Charge and Lewis Structure 49 Formal charge can help us choose the most likely Lewis structure. Example: There are 2 ways of writing the Lewis structure of nitrosyl chloride. Which one is the most stable Lewis structure?............ O.. Cl.. O N.. Cl.... N.. Structure 1 Structure 2 PRP1016 CHEMISTRY I | CENTRE FOR PRE-UNIVERSITY STUDIES PERSONAL USED ONLY | NOT FOR SALE  Made with Xodo PDF Reader and Editor Formal Charge and Lewis Structure 50 No. of No. of No. of valence e− bonding lone pair Formal charge = in free − ½ − − e e− atom The most stable Lewis structure is one with: No formal charges (0 charge on all atoms) The atoms bear the smallest charges The negative formal charges should appear on the most electronegative atoms Adjacent atoms in a structure should not carry formal charges of the same sign Formal charges on the atoms in a Lewis structure must total to zero for a molecule and to the net charge for a polyatomic ion. PRP1016 CHEMISTRY I | CENTRE FOR PRE-UNIVERSITY STUDIES PERSONAL USED ONLY | NOT FOR SALE  Made with Xodo PDF Reader and Editor Formal Charge and Lewis Structure 51 Structure 1:........ N O.. Cl.. Formal charge on N atom = 5 – ½(4) – 4 = -1 Although the net charge is zero, but Formal charge on O atom = 6 – ½(6) – 2 = +1 the more electronegative atom, O Formal charge on Cl atom = 7 – ½(2) – 6 = 0 have +1 charge. Structure 2:...... The Most Stable Structure.. O N.. Cl.. Formal charge on N atom = 5 – ½(6) – 2 = 0 Zero charge on all atoms Formal charge on O atom = 6 – ½(4) – 4 = 0 (No formal charge) Formal charge on Cl atom = 7 – ½(2) – 6 = 0 PRP1016 CHEMISTRY I | CENTRE FOR PRE-UNIVERSITY STUDIES PERSONAL USED ONLY | NOT FOR SALE  Made with Xodo PDF Reader and Editor 52 Exercise Draw 2 possible Lewis structures of carbon dioxide, CO2, in accordance with the octet rule. Then, select the most stable structure of carbon dioxide based on the formal charge. ANSWER: Two possible Lewis Structure A: B: PRP1016 CHEMISTRY I | CENTRE FOR PRE-UNIVERSITY STUDIES PERSONAL USED ONLY | NOT FOR SALE Made with Xodo PDF Reader and Editor  Made with Xodo PDF Reader and Editor Covalent to Ionic - A Continuum 53 Compounds frequently have bonding which is partially ionic and partially covalent. Mostly due to the different strength of nuclei in different elements. Example: Chlorine gas, Cl2 Example: Hydrogen Chloride gas, HCl...... Cl Cl H Cl............ Positive attraction from each chlorine When the 2 different atoms form a nucleus is the same. covalent bond , the attraction by the nuclei may be different. The pair of electrons in the bond is shared equally to form covalent The pair of electrons is no longer bond. equally shared. PRP1016 CHEMISTRY I | CENTRE FOR PRE-UNIVERSITY STUDIES PERSONAL USED ONLY | NOT FOR SALE  Made with Xodo PDF Reader and Editor Covalent to Ionic - A Continuum 54 Ionic Character in Covalent Bond Electronegativity - Measure of the attraction of an atom in a HF molecule for a pair of electron in a covalent bond. HCl The larger the difference in HBr electronegativity, the higher the ionic character. HI PRP1016 CHEMISTRY I | CENTRE FOR PRE-UNIVERSITY STUDIES PERSONAL USED ONLY | NOT FOR SALE  Made with Xodo PDF Reader and Editor 6.4 GEOMETRY AND SHAPES OF A MOLECULE 6.4.1 Valence-shell electron-pair repulsion (VSEPR) theory 6.4.2 Shapes of molecules 6.4.3 Factors affecting bond angle PRP1016 CHEMISTRY I | CENTRE FOR PRE-UNIVERSITY STUDIES 55 PERSONAL USED ONLY | NOT FOR SALE  Made with Xodo PDF Reader and Editor LEARNING OUTCOMES 56 By the end of this lecture, you should be able to: identify shape of covalent compounds explain the effect of lone pairs and electronegativity on the shape of covalent compounds predict the shape of covalent compounds PRP1016 CHEMISTRY I | CENTRE FOR PRE-UNIVERSITY STUDIES PERSONAL USED ONLY | NOT FOR SALE  Made with Xodo PDF Reader and Editor Valence-Shell Electron-Pair Repulsion 57 Theory (VSEPR) Molecules have Molecules with different Shape of Covalent bonds more than two arrangement of molecules can are highly atoms having a electron pairs be predicted by directional very definite around central VSEPR theory shape atom PRP1016 CHEMISTRY I | CENTRE FOR PRE-UNIVERSITY STUDIES PERSONAL USED ONLY | NOT FOR SALE  Made with Xodo PDF Reader and Editor VSEPR Theory 58 Rules to predict the shape of molecule The electron-pairs around the central atom repel each other A lone pair can exert a greater repelling effect than a bonding pair The order of repulsion between electron pairs is: Lone pair – lone pair > Lone pair – bond pair > Bond pair – bond pair For molecules and ions that do not contain lone pairs of electrons, the shape of the molecule or ions is the same as the geometry of electron-pairs PRP1016 CHEMISTRY I | CENTRE FOR PRE-UNIVERSITY STUDIES PERSONAL USED ONLY | NOT FOR SALE  Made with Xodo PDF Reader and Editor Shapes of Molecules 59 There are five basic geometry of electron-pairs. Geometrical arrangement of Number of electron pairs electron pairs 2 Linear 3 Trigonal planar 4 Tetrahedral 5 Trigonal bipyramidal 6 Octahedral PRP1016 CHEMISTRY I | CENTRE FOR PRE-UNIVERSITY STUDIES PERSONAL USED ONLY | NOT FOR SALE  Made with Xodo PDF Reader and Editor Shapes of Molecules 60 Number of electron pairs around central atom 3 4 5 6 Boron chloride, BCl3 Methane, CH4 Phosphorus(V) Sulphur(VI) fluoride, Example chloride, PCl5 SF6 Dot and cross S diagram H Cl F F Shape and Cl F F bond C P Cl S B H Cl F angle F F F H H Cl F 120˚ 109.5˚ 90˚ & 120˚ 90˚ Trigonal planar Tetrahedral – a Trigonal bipyramidal Octahedral – two Name of triangular-based – two tetrahedrons square-based shape pyramid with bases joined pyramids with bases joined PRP1016 CHEMISTRY I | CENTRE FOR PRE-UNIVERSITY STUDIES PERSONAL USED ONLY | NOT FOR SALE  Made with Xodo PDF Reader and Editor Effect of Lone Pair Electrons and 61 Electronegativity (A) Effect of lone pair electrons on the shape of molecules For molecules and ions that contain lone pairs of electrons, the shape of the molecule or ions is different from the geometry of electron-pairs. These shapes are called molecular shapes and refer to the positions of the atoms around the centre atom. PRP1016 CHEMISTRY I | CENTRE FOR PRE-UNIVERSITY STUDIES PERSONAL USED ONLY | NOT FOR SALE  Made with Xodo PDF Reader and Editor 62 Effect of Lone Pair Electrons on the Shape of Molecules Example 1: Methane, CH4 Ammonia, NH3 Water, H2O Molecules with H.. Four Electron-pairs C H There are 3 N H O molecular shapes H corresponding to 4 H H H H H electron-pairs that Tetrahedral Pyramidal V-shaped/Bent are arranged in 4 bonding pairs of 3 bonding pairs & 1 2 bonding pairs & 2 tetrahedral electron lone pair of electron lone pairs of electron orientation. PRP1016 CHEMISTRY I | CENTRE FOR PRE-UNIVERSITY STUDIES PERSONAL USED ONLY | NOT FOR SALE  Made with Xodo PDF Reader and Editor 63 Effect of Lone Pair Electrons on the Shape of Molecules Example 2: TeCl4 ClF3 Molecules with Five Cl F Electron-pairs Cl If the central atom is Te F Cl surrounded by 5 electron-pairs, the Cl lone pairs of electrons Cl F will always occupy the See-saw shape T-shaped space in the triangular 4 bonding pairs & 1 3 bonding pairs & 2 plane (equatorial lone pair of electron lone pairs of electron position). PRP1016 CHEMISTRY I | CENTRE FOR PRE-UNIVERSITY STUDIES PERSONAL USED ONLY | NOT FOR SALE  Made with Xodo PDF Reader and Editor 64 Effect of Lone Pair Electrons on the Shape of Molecules Example 3: Xenon tetrafluoride, XeF4 Molecules with Six.. Electron-pairs F F If a molecule has six Xe electron-pairs, the lone pair will always occupy F F the axial position... Square planar 4 bonding pairs & 2 lone pairs of electron Bond angles of 90˚ PRP1016 CHEMISTRY I | CENTRE FOR PRE-UNIVERSITY STUDIES PERSONAL USED ONLY | NOT FOR SALE  Made with Xodo PDF Reader and Editor Geometry of Electron pairs 65 Molecular shape electron pairs Total Bonding Lone Linear Linear 2 2 0 Trigonal planar Trigonal planar 3 0 3 Bent/V-shape 2 1 PRP1016 CHEMISTRY I | CENTRE FOR PRE-UNIVERSITY STUDIES PERSONAL USED ONLY | NOT FOR SALE  Made with Xodo PDF Reader and Editor Geometry of Electron pairs 66 Molecular shape electron pairs Total Bonding Lone Tetrahedral Tetrahedral 4 0 Trigonal pyramidal 3 1 4 Bent/V-shape 2 2 PRP1016 CHEMISTRY I | CENTRE FOR PRE-UNIVERSITY STUDIES PERSONAL USED ONLY | NOT FOR SALE  Made with Xodo PDF Reader and Editor Geometry of Electron pairs 67 Molecular shape electron pairs Total Bonding Lone Trigonal Trigonal bipyramidal bipyramidal 5 0 See-saw 4 1 T-shape 5 3 2 Linear 2 3 PRP1016 CHEMISTRY I | CENTRE FOR PRE-UNIVERSITY STUDIES PERSONAL USED ONLY | NOT FOR SALE  Made with Xodo PDF Reader and Editor Geometry of Electron pairs 68 Molecular shape electron pairs Total Bonding Lone Octahedral Octahedral 6 0 Square pyramidal 6 5 1 Square planar 4 2 PRP1016 CHEMISTRY I | CENTRE FOR PRE-UNIVERSITY STUDIES PERSONAL USED ONLY | NOT FOR SALE  Made with Xodo PDF Reader and Editor 69 Effect of Lone Pair Electrons and Electronegativity (B) Effect of electronegativity on the bond angle in H2O and H2S O Oxygen is more electronegative then sulphur H 104.5˚ H Bond pairs of electrons in the O-H bonds are drawn closer to the oxygen atom in H2O. S The repulsion between the bonding pairs is increased, thus the bond angle in H2O is H 92.5˚ H greater. PRP1016 CHEMISTRY I | CENTRE FOR PRE-UNIVERSITY STUDIES PERSONAL USED ONLY | NOT FOR SALE  Made with Xodo PDF Reader and Editor 70 Effect of Electronegativity on the Bond Angle Effect of electronegativity on the bond.. angle in NH3 and NF3 N F is more electronegative than H atom 107˚ H The bonding pair in N-F is closer to the F H H atom and further from the central atom, N... Thus the repulsion between the bonding N pairs in the NF3 molecule is less than that in NH3 molecule. 102˚ F F F PRP1016 CHEMISTRY I | CENTRE FOR PRE-UNIVERSITY STUDIES PERSONAL USED ONLY | NOT FOR SALE  Made with Xodo PDF Reader and Editor 71 Next Lecture PRP1016 CHEMISTRY I | CENTRE FOR PRE-UNIVERSITY STUDIES PERSONAL USED ONLY | NOT FOR SALE  Made with Xodo PDF Reader and Editor 6.5 POLARITY 6.5.1 Bond polarity 6.5.2 Polarity of molecules PRP1016 CHEMISTRY I | CENTRE FOR PRE-UNIVERSITY STUDIES 72 PERSONAL USED ONLY | NOT FOR SALE  Made with Xodo PDF Reader and Editor LEARNING OUTCOMES 73 By the end of this lecture, you should be able to: identify polar and non-polar molecules PRP1016 CHEMISTRY I | CENTRE FOR PRE-UNIVERSITY STUDIES PERSONAL USED ONLY | NOT FOR SALE  Made with Xodo PDF Reader and Editor Polar and Non-Polar Molecules 74 Determination of polar or non-polar molecule depends on the distribution of electrons A polar molecule is one in which one side, of the molecule has a slight positive charge and the other side, has a slight negative charge symmetrical Molecule Uneven/unsymmetrical distribution of Non-polar Polar distribution of charge charge PRP1016 CHEMISTRY I | CENTRE FOR PRE-UNIVERSITY STUDIES PERSONAL USED ONLY | NOT FOR SALE  Made with Xodo PDF Reader and Editor Polar and Non-Polar Molecules 75 Polar bond forms from unequally shared electrons. Consists of two poles: partially positive (δ+) and partially negative (δ–). The greater the differences in the electronegativity, the more polar of the bond. The electronegativity can be represented by the Pauling scale. + δ δ− H Cl PRP1016 CHEMISTRY I | CENTRE FOR PRE-UNIVERSITY STUDIES PERSONAL USED ONLY | NOT FOR SALE  Made with Xodo PDF Reader and Editor Polar and Non-Polar Molecules 76 The Pauling Scale PRP1016 CHEMISTRY I | CENTRE FOR PRE-UNIVERSITY STUDIES PERSONAL USED ONLY | NOT FOR SALE  Made with Xodo PDF Reader and Editor Polar and Non-Polar Molecules 77 Molecular dipole moment (μ) A measure of the polarity of a covalent bond. The vector sum of the individual bond dipole moments in a molecule measured in unit Debye (D) Bond Bond dipole Bond Bond dipole Bond Bond dipole (D) (D) (D) H–C 0.3 C–F 1.6 C–O 0.7 H–N 1.3 C–Cl 1.5 C=O 2.3 H–O 1.5 C–Br 1.4 C–N 0.2 H–S 0.7 C–I 1.2 C=N 3.5 PRP1016 CHEMISTRY I | CENTRE FOR PRE-UNIVERSITY STUDIES PERSONAL USED ONLY | NOT FOR SALE  Made with Xodo PDF Reader and Editor Polar and Non-Polar Molecules 78 Some molecules that contain polar bonds have no overall polarity. This occurs when the dipole moment from each of the bonds cancel in the molecules as a whole. This happens in molecules that are symmetry such as with linear shape (CO2) and tetrahedral shape (CCl4). Cl δ− δ+ δ+ C δ+ δ− δ+ δ− Cl Cl δ− Cl PRP1016 CHEMISTRY I | CENTRE FOR PRE-UNIVERSITY STUDIES PERSONAL USED ONLY | NOT FOR SALE  Made with Xodo PDF Reader and Editor Polar and Non-Polar Molecules 79 To determine the polarity of a molecule, we need to identify: 1. whether the molecule has dipole moments or not 2. the arrangement of these bonds in space PRP1016 CHEMISTRY I | CENTRE FOR PRE-UNIVERSITY STUDIES PERSONAL USED ONLY | NOT FOR SALE  Made with Xodo PDF Reader and Editor Polar and Non-Polar Molecules 80 When the centers of negative and positive charge are separated, we say that the molecule has a dipole moment. + δ δ− H Cl Molecular geometry is a critical factor in determining if a molecule has a dipole moment. PRP1016 CHEMISTRY I | CENTRE FOR PRE-UNIVERSITY STUDIES PERSONAL USED ONLY | NOT FOR SALE  Made with Xodo PDF Reader and Editor Polar and Non-Polar Molecules 81 These molecules have polar bonds, but each has a zero resultant dipole moment, hence are non-polar molecules. F Cl O C O B F C F Cl Cl Cl Carbon dioxide Boron trifluoride Carbon tetrachloride μ=0D μ=0D μ=0D PRP1016 CHEMISTRY I | CENTRE FOR PRE-UNIVERSITY STUDIES PERSONAL USED ONLY | NOT FOR SALE  Made with Xodo PDF Reader and Editor Polar and Non-Polar Molecules 82 These molecules possess resultant dipole moment, hence are polar molecules. Direction of resultant Direction of resultant Direction of resultant dipole moment dipole moment dipole moment H H N C O O H H H H H Formaldehyde Water Ammonia μ = 2.33 D μ = 1.85 D μ = 1.47 D PRP1016 CHEMISTRY I | CENTRE FOR PRE-UNIVERSITY STUDIES PERSONAL USED ONLY | NOT FOR SALE  Made with Xodo PDF Reader and Editor Polar and Non-Polar Molecules 83 cis-trans isomers often differ in the magnitude of their dipole moments and a polar compound. H H H Cl C C C C Cl Cl Cl H Direction of Zero resultant dipole resultant dipole moment moment cis-Dichloroethene trans-Dichloroethene PRP1016 CHEMISTRY I | CENTRE FOR PRE-UNIVERSITY STUDIES PERSONAL USED ONLY | NOT FOR SALE  Made with Xodo PDF Reader and Editor 84 Exercise Choose the molecule(s) that has polar bonds but considered as a non polar molecules: Hydrogen cyanide, Ozone, O3 Borane, BH3 Sulphur trioxide, O3 HCN ANSWER: PRP1016 CHEMISTRY I | CENTRE FOR PRE-UNIVERSITY STUDIES PERSONAL USED ONLY | NOT FOR SALE  Made with Xodo PDF Reader and Editor 85 Exercise Identify whether the following liquids are polar or non-polar: a) Liquid Nitrogen, N2 b) Hydrogen Flouride, HF ANSWER: c) Benzene, C6H6 d) Methanol, CH3OH PRP1016 CHEMISTRY I | CENTRE FOR PRE-UNIVERSITY STUDIES PERSONAL USED ONLY | NOT FOR SALE  Made with Xodo PDF Reader and Editor 6.6 HYBRIDISATION 6.6.1 Bonding theory 6.6.2 Hybridisation of orbital PRP1016 CHEMISTRY I | CENTRE FOR PRE-UNIVERSITY STUDIES 86 PERSONAL USED ONLY | NOT FOR SALE  Made with Xodo PDF Reader and Editor LEARNING OUTCOMES 87 By the end of this lecture, you should be able to: explain bonding theory explain hybridisation of orbitals PRP1016 CHEMISTRY I | CENTRE FOR PRE-UNIVERSITY STUDIES PERSONAL USED ONLY | NOT FOR SALE  Made with Xodo PDF Reader and Editor Bonding Theory 88 Bonding theory Bonds are assumed to be formed by overlap of atomic orbitals. The strength of covalent bond is proportional to the area where the atomic orbitals overlap. The sigma (σ) bond is form by the head-on overlapping. The pi (π) bond is form from sideways overlapping. PRP1016 CHEMISTRY I | CENTRE FOR PRE-UNIVERSITY STUDIES PERSONAL USED ONLY | NOT FOR SALE  Made with Xodo PDF Reader and Editor Bonding Theory 89 The head-on overlapping Example 1: Formation of covalent bond between two hydrogen atoms 1s 1s 1s 1s H ↑ ↑ H H ↑↓ H Sigma (σ) bond is formed by head-on overlapping between two 1s orbitals from each hydrogen atoms PRP1016 CHEMISTRY I | CENTRE FOR PRE-UNIVERSITY STUDIES PERSONAL USED ONLY | NOT FOR SALE  Made with Xodo PDF Reader and Editor Bonding Theory 90 The head-on overlapping Example 2: Formation of covalent bond between hydrogen atom and fluorine atom 1s ↓↑ F 2p H Sigma (σ) bond is formed by head-on overlapping between 1s orbitals from hydrogen atom and 2p orbital from fluorine atom PRP1016 CHEMISTRY I | CENTRE FOR PRE-UNIVERSITY STUDIES PERSONAL USED ONLY | NOT FOR SALE  Made with Xodo PDF Reader and Editor Bonding Theory 91 The head-on overlapping Example 3: Formation of covalent bond between two fluorine atoms 2p F ↓↑ F 2p Sigma (σ) bond is formed by head-on overlapping between two 2p orbital from each fluorine atoms PRP1016 CHEMISTRY I | CENTRE FOR PRE-UNIVERSITY STUDIES PERSONAL USED ONLY | NOT FOR SALE  Made with Xodo PDF Reader and Editor Bonding Theory 92 The sideways overlapping Example 1: Formation of double bond between two carbon atoms ↑↓ Pi (π) bond C ↑↓ C Sigma (σ) bond Pi (π) bond is formed by sideways overlapping between two 2p orbitals from each carbon atoms PRP1016 CHEMISTRY I | CENTRE FOR PRE-UNIVERSITY STUDIES PERSONAL USED ONLY | NOT FOR SALE  Made with Xodo PDF Reader and Editor Hybridisations of s and p orbitals 93 Hybridisation The process of mixing together two or more atomic orbitals that have the similar energies is called hybridisation. The new atomic orbitals produced are called hybrid orbitals. 2p Energy sp3 2s Unhybridised Hybridised PRP1016 CHEMISTRY I | CENTRE FOR PRE-UNIVERSITY STUDIES PERSONAL USED ONLY | NOT FOR SALE  Made with Xodo PDF Reader and Editor Hybridisations of s and p orbitals 94 Type of sp sp2 sp3 sp3d1 sp3d2 hybridisation one s one s one s one s one s Hybrid orbitals three p three p one p two p three p one d two d Tetrahedral, Octahedral, Shape of Trigonal trigonal Trigonal Square linear molecules planar, bent pyramidal, bipyramidal pyramidal, bent square planar BF3 CH4 BeCl2 PCl5 SF6 Examples O3 H2 O C2H2 C2H4 NH3 PRP1016 CHEMISTRY I | CENTRE FOR PRE-UNIVERSITY STUDIES PERSONAL USED ONLY | NOT FOR SALE  Made with Xodo PDF Reader and Editor Hybridisations of s and p orbitals 95 Example 1: Carbon in Methane In isolated C atom, the 2s and all 2p orbitals are mixed to form sp3 hybrid orbitals (hybridized C atom) In methane, the sp3 hybrid orbitals overlap with the half-filled 1s orbitals of four hydrogen atoms and formed four C−H bonds which point toward the vertices of a tetrahedral. H ↑↓ ↑ ↑ mix ↑ ↑ ↑ ↑ 1s 2s 2p 2p 2p sp3 sp3 sp3 sp3 sp3 Isolated C atom Hybridised C atom sp3 C sp3 H 1s sp3 H 1s H 1s PRP1016 CHEMISTRY I | CENTRE FOR PRE-UNIVERSITY STUDIES PERSONAL USED ONLY | NOT FOR SALE  Made with Xodo PDF Reader and Editor Hybridisations of s and p orbitals 96 Example 2: Nitrogen in Ammonia One of the sp3 orbitals is filled with a lone pair electrons. Shape : Trigonal pyramidal ↑↓ ↑ ↑ ↑ mix ↑↓ ↑ ↑ ↑ 2s 2p 2p 2p sp3 sp3 sp3 sp3 sp3 Isolated N atom Hybridised N atom sp3 N sp3 H 1s sp3 H 1s H 1s PRP1016 CHEMISTRY I | CENTRE FOR PRE-UNIVERSITY STUDIES PERSONAL USED ONLY | NOT FOR SALE  Made with Xodo PDF Reader and Editor Hybridisations of s and p orbitals 97 Example 3: Boron in BF3 Central B atom is sp2 hybridized. Each sp2 orbital overlaps with the 2p orbital of an F atom, forming 3 bonding pairs. ↑↓ ↑ mix ↑ ↑ ↑ 2s 2p 2p 2p sp2 sp2 sp2 Isolated B atom Hybridised B atom PRP1016 CHEMISTRY I | CENTRE FOR PRE-UNIVERSITY STUDIES PERSONAL USED ONLY | NOT FOR SALE  Made with Xodo PDF Reader and Editor Hybridisations of s and p orbitals 98 Example 4: Carbon in Ethene The unhybridised p orbitals are able to overlap, resulting in the formation of a second bond (π bond). π p H H sp2 sp2 sp2 C σ C sp2 sp2 H H PRP1016 CHEMISTRY I | CENTRE FOR PRE-UNIVERSITY STUDIES PERSONAL USED ONLY | NOT FOR SALE  Made with Xodo PDF Reader and Editor 99 Exercise State the type of hybridization of the central atom in the following molecules: a) BH3 b) SF6 c) PCl5 ANSWER: d) H2O PRP1016 CHEMISTRY I | CENTRE FOR PRE-UNIVERSITY STUDIES PERSONAL USED ONLY | NOT FOR SALE  Made with Xodo PDF Reader and Editor 100 Next Lecture PRP1016 CHEMISTRY I | CENTRE FOR PRE-UNIVERSITY STUDIES PERSONAL USED ONLY | NOT FOR SALE  Made with Xodo PDF Reader and Editor 6.7 INTERMOLECULAR FORCES AND HYDROGEN BONDING 6.7.1 Van der Waals forces 6.7.2 Hydrogen bond PRP1016 CHEMISTRY I | CENTRE FOR PRE-UNIVERSITY STUDIES 101 PERSONAL USED ONLY | NOT FOR SALE  Made with Xodo PDF Reader and Editor LEARNING OUTCOMES 102 By the end of this lecture, you should be able to: describe intermolecular forces differentiate types of Van der Waals forces describe hydrogen bonding PRP1016 CHEMISTRY I