04 chemical bonds


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04 chemical bonds

  1. 1. 1 byby CHEMISTRY DEPARTMENTCHEMISTRY DEPARTMENT CHEM-111CHEM-111 General ChemistryGeneral Chemistry Unit fourUnit four Chemical BondsChemical Bonds
  2. 2. 2 CHEMICAL BONDS 1. Valence electrons 2. Electron dot structures 3. Molecules and Ions 4. Formation of Ions 5. Ionic bonds and Ionic compounds 6. Covalent bonds and molecular compounds 7. Coordinate Covalent bonds 8. Bond polarity 9. Attraction between molecules 10. Shapes of molecules
  3. 3. 3 Chemical Bonding Classification Intramoleculr bonding Force of attraction within the molecule determine Chemical properties Ionic Bonds between ions Force of attraction between two or more molecules determine Physical properties i. Dipole-Dipole attraction ii. Hydrogen Bonding iii.London Forces Intermolecular bonding Bonds are formedBonds are formed Covalent Bonds between Nonmetals Nonpolar Polar
  4. 4. 4 I- Intramolecular ChemicalI- Intramolecular Chemical BondingBonding
  5. 5. 5 I- Intramolecular ChemicalI- Intramolecular Chemical BondingBonding Intramolecular chemical bonding refers to the attractive forces that holds the atoms together to form a molecule H2, O2, CH4 NaCl, MgCl2 etc. Major classes I) Ionic bonds II) Covalent bonds
  6. 6. 6 Because All atoms would like to attain (reach) stable electron configurations like noble gases by: losing electrons or sharing electrons or gaining electrons. For a stable configuration each atom must fill its outer energy level: 1st : 2 electrons 2nd : 8 electrons 3rd : 8 electrons 4th : 8 electrons Reason for Intramolecular Chemical Bonding
  7. 7. 7 Valence Electrons The electrons in outer shell are called valence electrons. These electrons are very influential (important) as they determine chemical properties of the elements. For representative elements, the number of valence electrons in an atom is equal to the group number. Li C S Group Number 6AIA 4A
  8. 8. 8 Core Electrons . Electrons present in shells below the outer shell are called core electrons Core electrons Valence electrons
  9. 9. 9 Group Number and Arrangement of Valence Electrons Group Selected Electron Number of Electron-Dot Number Elements Arrangement Valence Electrons Structure 1A Li 2-1 1 2A Ca 2-8-2 2 3A Al 2-8-3 3 4A C 2-4 4 5A N 2-5 5 6A S 2-8-6 6 7A Cl 2-8-7 7 8A Ne 2-8 8 Li Ca Al C N S Cl Ne
  11. 11. 11 Types of intramolecular Bonding I-Ionic Bonding Ionic bonds are formed due to the transfer of electrons from one atom (metal) to another atom (nonmetal) to give oppositely charged particles called ions to attain a noble gas arrangement. Electrically charged atoms or groups of atoms are called ions. They are very reactive species H+ , Li+ , OH- , Br- etc
  12. 12. 12 Types of ions 1- Positive Ions (Cations) Positively charged ions: H+, Na+, K+, Ca+ They are formed by loss of an electron (size of cation is smaller than atom BECAUSE A CATION LOSES A SHELL). 2-Negative Ions ( Anions ) Negatively charged ions: Cl- , OH- , I- They are formed by gain of an electron (size of anion is bigger than corresponding atom because entering electron and electrons already present, repel each other and shell get enlarged).
  13. 13. 13 To form an ion, an element has to lose or gain electrons and form stable full outer shell of a noble gas Electronic configuration of lithium, carbon and fluorine Atomic number 3 Lithium Electronic configuration 2,1 Atomic number 6 Carbon Electronic configuration 2,4 Atomic number 9 Fluorine Electronic configuration 2,7 Which elements form ions? Many non metals can gain electrons to form negatively charged ions Some non metals with partly filled electrons shell do not form ions All metals can lose electrons to form positively charged ions
  14. 14. 14 IA IIA IIIA IVA VA VIA VIIA Li+ Be2+ C4- N3- O2- F- Na+ Mg2 Al3+ Si4- P3- S2- Cl- K+ Ca2+ Se2- Br- Rb+ Sr2+ Te2- I- Cs+ Ba2+ Group Number Ions formed by the representative elements +
  15. 15. 15 A positive ion produced by loss of one or more electrons from metal atom. Li+ , Na+ ,K+ , Mg2+, Ca2+ , Al3+ , etc. Anion A negative ion formed by gain of one or more electrons by non metal. F1- ,Cl1- , O2- , N3- , C4- etc X c Charge Element Ions formed by the Representative Elements Cation
  16. 16. 16 Ionic bonds are formed between a metal and a non-metal. Bonding occurs using valence electrons. Ionic Bonding and Octet Rule •Atoms that have 5, 6 or 7 electrons in their outer levels will tend to gain electrons from atoms with 1, 2 or 3 electrons in their outer levels •Atoms that have 1, 2 or 3 electrons in their outer levels will tend to lose them in interactions with atoms that have 5, 6 or 7 electrons in their outer levels. •Atoms try to get 8 electrons in the valence shell (octet rule)
  17. 17. 17 Formation of sodium chloride or common salt •Na atom looses an electron and forms Na+ ion. •Cl atom gains an electron and forms Cl- ion. NaCl (Ionic compound) Oppositely Charged ions, Na+ and Cl- attract each other and form ionic compound, NaCl. Cl+Na + - Cl - Na + Na Na+ cations anions + e + eCl - Cl
  18. 18. 18 Ionic Giant Molecule of NaCl Ionic Giant Molecule Cl Cl Cl Na Na Na Cl Na Na Cl Na Cl Cl Cl Na Cl Na Cl Cl Na Cl Na Na Cl Na Na Na Cl Cl Na Cl Na Na Cl Cl Na Cl Cl Cl Na Cl Na Cl Na Na Cl Na Cl Na Na Na Cl Na Cl Cl Na Cl Cl Cl Na Na Na Cl+ Atoms A Atoms B Many atoms Electrons transfered from atoms A to atoms B Na Cl •Ionic bond is the attraction between cations and anions •Na+ and Cl- ions are stacked together •Lowest energy arrangement •The pattern is repeated throughout the crystal or Lattice Cl
  19. 19. 19 Loses 2e- Each gains 1e- One Magnesium ion Mg2+ Two Chloride ions 2Cl- Magnesium and Chloride ions Combine to form MgCl2 (Magnesium chloride) Formation of Magnesium chloride MgCl2 Mg Mg2+ ClCl Cl Cl
  20. 20. 20 Lewis structure • Lewis symbols help us to find the valence electrons and predicts bond Na. + :Cl... .. Na+ :Cl: .. .. - Mg 2:Cl... .. Mg :Cl: .. .. -2+ 2 . . + Magnesium chloride Sodium chloride
  21. 21. 21 PROPERTIES OF IONIC COMPOUND a. They have high melting and boiling points due to presence of strong intermolecular force of attraction. b. They are non-volatile: they do not easily turn into gas. c. Generally soluble in water because they generally ionize in water. d. Solids do not conduct electricity because the ions are held together by strong electrostatic force of attraction. e. Conduct electricity when melted. f. Aqueous solution conducts electricity because the ions are mobile in solutions. g. They are generally insoluble in organic solvents, because organic solvents are covalent compounds.
  22. 22. 22 The noble gases are known for their chemical stability and existence as mono atomic molecules as they contain 8 electrons in outer most shell (valence shell) except Helium Nobel gases He Ne Ar Kr Xe Rn Valence electrons 2 8 8 8 8 8 Period no. 1 2 3 4 5 6 No. of shells 1 2 3 4 5 6 Other atoms also want electronic configurations just like noble gases (concept of duplet & octet rules) due to their Stability so they form ionic bond Why Ionic Bond are Formed? Reasons 1.Stability of noble Gases
  23. 23. 23 Li 1 1 H 2 3 He C 6 12 4 7 Be B C N O F Ne 4 5 6 7 8 9 10 9 11 12 1614 19 20 Na Mg Al Si P S Cl Ar 11 12 13 14 15 16 17 18 23 24 27 28 31 32 35.5 40 K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr 19 20 21 2223 24 25 26 27 28 29 35 3630 31 32 33 34 39 40 45 48 51 52 55 56 Rb Sr Y Zr NbMo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe Cs Ba Lu Hf Ta W Re Os Ir Pt Au Hg Ti Pb Bi Po At Rn Fr Ra Lr Rf Db Sg Bh Hs MtUunUuuUub UutUuq Uuh IA IIBIIIB IVB VIBVB VIIB VIIIB IB IIA IIIA IVA VA VIA VIIA VIIIA 1 2 3 4 5 6 7 8459 59 63.5 65 70 73 75 79 80 38 39 4037 41 42 43 44 4645 47 48 49 50 51 52 53 54 La Ce Pr NdPm Sm Eu Gd Tb Dy Ho ErTm Yb Ac Th Pa U Np PuAmCm Bk Cy EsFm Md No 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 89 88 90 91 92 93 94 95 96 97 98 99 101100 102 103 104 105 106 107 108 109 110 111 112 113 114 116 85.5 88 89 91 93 96 (98) 101 103 106 108 112 115 119 122 131 133 137 128 127 175 178.5 181 184 186 190 192 195 197 201 204 207 209 (209) (210) (222) (223) 226 (260) (261) (262) (263) (262) (265) (266) (269) (272) (277) (289) (289) 138 140 141 144 (145) 150 152 157 159 162.5 165 167 169 173 227 232 231 238 237 (244) (243) (247) (247) (251) (252) (257) (258) (259) NON METAL C H Hg SOLID GAS LIQUID METAL METALLOID PERIODIC TABLE OF ELEMENTS
  24. 24. 24 ………… ... +………………………….. (a) (b) (c) (d) 75pm 75 -436 0 Distance between hydrogen nuclei (pm) Potentialenergy(k/mol) 2.Change in Potential Energy Formation of ionic compound must be exothermic i.e. P.E of ionic compound (product) is less than reactants atoms. Why Ionic Bond are Formed?
  25. 25. 25 Simple Binary (double) Compounds of Metals and a NonmetalsSimple Binary (double) Compounds of Metals and a Nonmetals • One element is metal and the other is a non-metal • The metal (+ve) is name first, followed by the nonmetal (-ve) • Only two different elements are present • Number of each is given as a subscript • Overall formula must have no Charge Examples: metal nonmetal NaCl Sodium chloride SrO Strontium oxide Al2S3 Aluminum sulfide Binary compounds= Compound composed of two different elements In ionic compounds one is metal and the other is non- metal.
  26. 26. 26 Naming ionic compounds IUPAC Methods of Naming • Firstly, Name the cation (metal) • When an element has only one charged state • Secondly, Name the anion (nonmetal) using the ending (-ide) • Examples CrCl3 Chromic chloride, MgBr2 Magnesium bromide, Al2O3 Aluminum oxide, K3N Potassium nitride, MgS Magnesium sulfide Ca2C Calcium carbide SrO Strontium oxide
  27. 27. 27 Formula for some ionic compounds NaCl MgCl2 AlCl3 Na2O MgO Al2O3 Na3N Mg3N2 AlN Some simple ions Cations Na+ Mg2+ Al3+ Anions Cl- O2- N3- Simple short cut can be used to obtain the formula of an ionic compound by exchanging superscript for subscript Naming of Ionic Compounds Ca 2 + Ca3(PO4)2 PO4 3 -Al 3 O 2 Al 2O 3 -+
  28. 28. 28 Naming ionic compounds B group metals may have more than one possible charge ( due to more than one oxidation state). Use roman numerals (I,II,III) in the name to indicate the charge on the metal. . Cu1+ + O2- = Cu2O copper (I) oxide copper (I) oxide Cu2+ + O2- = CuO copper (II) oxide copper (II) oxide
  29. 29. 29 Naming ionic compounds FeBr3 Each bromide is 1- so iron 3+ FeBr3 Iron (iii) bromide FeCl2 iron (ii) chloride FeCl3 iron (iii) chloride SnBr2 tin (ii) bromide SnBr4 tin (iv) bromide AgCl silver chloride CdS cadmium sulfide There are some exception Some B metals only have a single state so the roman numeral may be omitted Some A metals have more than one State so numbers must be used
  30. 30. 30 Some ions have characteristic colors they impart to their compounds as seen below Solution of potassium chromate, which contains the yellow chromate ion,CrO4 2- . Polyatomic ions Solution of potassium permanganate, which contains the violet permanganate Ion, MnO4 - Solution of potassium dichromate ion, Cr2O7 2- . A poly atomic ion is a group of nonmetal atoms (which are covalently bonded together), that carries electrical charge
  31. 31. 31 Some common polyatomic ions Cation Name of cation Anion Name of anion NH4+ ammonium ClO2 - chlorite H3O+ hydronium ClO- or OCl- hypochlorite PO4 3- phosphate HPO4 2- hydrogen phosphate H2PO4- dihydrogen phosphate CrO4 2- chromate Cr2O7 2- dichromate MnO4- permanganate CH3CO2- acetate NO3- nitrate OH- hydroxide O2 2- peroxide SO4 2- sulphate
  32. 32. 32 AgNO3 silver nitrate H2O2 hydrogen peroxide Fe2(SO4)3 iron (III) sulphate Naming compounds containing polyatomic ions Most polyatomic ions have names that end with -ate or- ide. NH4Cl ammonium chloride NaOH sodium hydroxide KMnO4 potassium permanganate (NH4)2SO4 ammonium sulfate Write the positive ion, first, and then write the name of the polyatomic ion
  33. 33. 33 Chemical Formulas of complex compounds Example: Copper sulfate CuSO4.5H2O CuSO4.5H2O. Blue crystal CuSO4 White powder heat
  35. 35. 35 Bonds are formed between two non metals by sharing of one or more pairs of electrons. CH4 , CCl4, O2 , H2, H2O, HCl, HF , NH3, CO2 COVALENT BONDS The attractive forces between two atoms dominate (take over) the repulsive forces. Total potential energy decreases as a result bond is formed at a short distance, called bond distance.
  36. 36. 36 P P PP P PP P e- e- e- e- e- e- e- e- D Combination of forces A No interaction B Attraction begins C Covalent bond + + + ++ + + + Formation of covalent bondFormation of covalent bond Both nuclei repel each other, as both electron clouds do The nucleus of one atom attracts the electron clouds of the other atom , vice versa electron share
  37. 37. 37 Formation of Covalent Bond Example: Formation of ICl Molecule Atom B + Two atoms Electron pair shared Between atom A and Atom B Atom A Atom B Atom A Chlorine + Two atoms Electron pair shared between iodine and Iodine chlorine Iodine Chlorine
  38. 38. 38 C H H H H 1. H. + . H H :H or H­H 2. H. + . F H : F or H­F Or4H. H:C:H : : H H 3. + C methane H2 HF CH4 Examples Electron-Dots Structures Molecular Models
  39. 39. 39 x x x x xx x x x x xx xx x x Cl x x x x xx x x x x xx xx Cl x x Cl2 molecule a shared electron pair forms a single covalent bond Other ways of showing a chlorine molecule: Other ways showing a hydrogen chloride molecule: H-Cl HCl molecule x x x x xx x x x x xx xx Cl x x x x H Covalent Compounds Cl-Cl
  40. 40. 40 x x x x x x x x x x x x x O O x x An oxygen molecule two shared electrons pairs form a double covalent bond double bond A nitrogen molecule Other ways of showing a nitrogen molecule x x x x x x x x x x x N x x Nx three shared electrons pairs form a triple covalent bond triple bond Other ways of showing an oxygen molecule Multiple Covalent Compounds
  41. 41. 41 Lewis Structure H H Two electrons Two electrons When two hydrogen atoms share a pair of electron the covalent bond is formed. 1. H• + H • → H••H H H H H CC + 4H2.
  42. 42. 42 More Examples of Lewis Structure H N H H H F H H O O OC O C O Eight electrons O C O Multiple Covalent Bonds Covalent Bonds
  43. 43. 43 COORDINATE COVALENT BONDS • The type of bond, in which a pair of electrons from one atom is shared by two atoms, is called a coordinate covalent bond. Example The reaction of boron tri-chloride, BCl3, and ammonia, NH3. H N: H H + B Cl Cl Cl H N H H Cl Cl Cl B: H N H H Cl Cl Cl B Coordinate covalent bond.
  44. 44. 44 PROPERTIES OF COVALENT COMPOUNDS a. Low melting and boiling points because of weak intermolecular binding force b. They are generally volatile because of their low M.P. and B.P. c. They are mostly insoluble in water d. Even if some covalent compounds dissolve in water they do not form ion and remain almost undissociated. e. They are generally soluble in organic solvents. f. They are non-conductors of electricity in solid state.
  45. 45. 45 Polarity of molecules Electrons in a covalent bond rarely get shared equally. Unequal sharing results in polar bondsH F Slight positive side Slight negative side Smaller electro negativity Larger electro negativity Polar covalent bonds Electrons may not be shared equally. This is based on the electro-negativity difference between the two elements forming the bond. If: 1.Electronegativity difference > 1.7 (ionic bond) 2.Electronegativity difference = 0 (covalent non-polar bond) 3.Values between 0 and 1.7 are polar covalent bond – In polar covalent electrons are not shared equally
  46. 46. 46 Electro-negativity increases across the period & decreases down the group Increase Decreases
  47. 47. 47 Shapes of Molecules Electron Dot Bonded Molecular Molecule Structure Atoms Shape (angle) CH4 4 tetrahedral (1090 ) NH3 3 pyramidal (1090 ) H2 O 2 bent (1090 ) H H H H C H N H H H H O BCl3 3ClBCl Cl planar-trigonal
  48. 48. 48 Molecular Geometry Molecules have specific shapes which is determined by the number of electron pairs around the central species. An electron group can be the electron pairs bonded to atoms or a lone pair. Geometry affects factors like polarity and Solubility. Multiple bonds are treated as a single bond for geometry
  49. 49. 49 Characteristic physical properties Boiling point The temperature at which a liquid is converted to a gas at atmospheric pressure. Melting point The temperature at which a solid is converted to a liquid. Compounds Bond Mp Bp N2 nonpolar -210 -196 O2 nonpolar -219 -183 NH3 polar -78 -33 H2O polar 0 100 NaCl ionic 804 ?
  50. 50. 50 II- Intermolecular Attractions
  51. 51. 51 Forces between Molecules that determine Physical properties Intermolecular Attractions Types of Intermolecular Attractions 1 Dipole – dipole attractions 2. Hydrogen Bonding 3. London Forces
  52. 52. 52 These attractions are weaker than ionic or covalent bonds (i.e. only 1% strong). These attraction are due to the electrons which make the bond but are not equally shared between atoms because of a difference in electro-negativity of these atoms. δ+ and δ- ends are attracted to each other . δ+ δ- δ+ δ- δ+ δ- 1- Dipole–Dipole Attractions
  53. 53. 53 2. Hydrogen Bonding (dipole-dipole interaction) The attraction between a hydrogen atom in one molecule and an electronegative atom (F,O,N) in another molecule is hydrogen bonding Hδ+ —Fδ- …… Hδ+ —Fδ- …… Hδ+ —Fδ- This attraction is responsible for high boiling point of water
  54. 54. 54 Polar water molecule Hydrogen bonding Hydrogen bonding produces strong attractions between water molecules H O H H O H Hydrogen bonding in water The water molecule is very polar
  55. 55. 55 Water Ice The density of ice is 0.931 gm/cubic cm. This compares with a density of 1.00 gm/cubic cm. for water so ice floats on water H H H O O O O O H H H H H H H In liquid water each molecule is hydrogen bonded to approximately 3- 4 other water molecules In ice each molecule is tetrahedrally hydrogen bonded to 4 other molecules. which controls the orientation such that ice has empty spaces which makes ice lighter Tetrahedral shape Density of Ice
  56. 56. 56 3.London Dispersion Forces Van der Waal forces The attraction of positively charged nucleus of one atom for electron cloud of an atom in nearby molecule. These are relatively weak forces and exist in symmetrical non-polar molecules like CH4, SO3, CO2, O2, H2, He Random motion of electrons for instant causes electrons more on one side & instantaneous dipole is produced that induces a dipole in its neighbor.
  57. 57. 57 London forces As the dipole forms in atom A, it induces a dipole in atom B London forces are momentary and called instantaneous dipole A B δ-δ+ δ+ δ-
  58. 58. 58 The electron density fluctuates in two neighboring atoms, giving rise to fleeting attractions between the momentary dipoles. δ+ δ− δ−δ+ δ− δ+ δ− δ+ δ+ δ− Flickering On and Off of the Dipoles No Polarization Instantaneous Dipoles on atom A induces a dipole on atom B A B A B
  59. 59. 59 Exercise CHEMICAL BONDING M.C.Q: Choose the best answer. 1. Force of attraction that holds atoms in a molecule together is: a) covalent bond b) ionic bond c) chemical bond d) coordinate bond 2. If atoms gain or lose electron, they will form: a) ions b) cations c) anions d) Polar covalent bond 3. Indicate the members of nonmetals: a) Lithium b) Oxygen c) Chlorine d) both b & c
  60. 60. 60 M.C.Q 4. The formation of ions from neutral atoms is nearly always: a) endothermic b) exothermic c) both a & b. d) none of the above 5. In making bonds atoms obey octet rule, so number of electrons in their outer shell may be: a) 2 or 8 electrons b) 6 or 8 electrons c) 8 or 10 electrons d)18-electrons 6. Choose the polar compound: a) CH4 b) NaCl c) HCl d) Both a & c 7. The bond formed in CH4 molecule is by: a) Loss of electrons b) Gain of electrons c) Sharing of electrons d) Both a & b
  61. 61. 61 8. The loss of electron/electrons from outer shell of metals make them: a) positive ion and smaller in size than corresponding atom b) negative ion and smaller than atom c) positive ion and bigger than atom 9. Gain of electron/electrons by non metals changes them into: a) positive ions b) negative ions c) neutral atoms d) both a & b 10. Example of anion: a) K+ b) O- 2 c) Mg +2 d) Na 11. Ionic compounds: a). HF b) Ca O C) H2O d). Both a & b
  62. 62. 62 12. If difference between electro negativity values of the atoms is > 1.7 they will form: a) Ionic bond b) Covalent bond c) Polar covalent bond d) Non polar covalent bond 13. The force of attraction among water, H2O ,molecules is: a) Dipole-dipole interaction b) London forces c) Hydrogen bonding d) None of the above. 14The molecule that shows London dispersion forces is: a) NaCl b) CO2 c) H2O d) MgO 15. What are Intermolecular Forces? a) Hydrogen bonding b) London Forces c) Dipole-dipole interaction d) All of these
  63. 63. 63 16. The atoms complete their outer shells by obeying octet rule and attain electronic configuration of: a) Alkali metals b) Halogens c) noble gases d) Transition metals 17. Energy required to break a chemical bond & form a neutral isolated atom is called: a) Bond energy b) Bond order c) Bond distance d) both a & b 18. Find out the chemical formula of organic solvent named carbon tetra chloride: a) :CCl2 b) CH4 c) CCl4 d) CHCl3 19. Identify the ionic molecule: a) NH3 b) N2 c) H2O d) NaCl