module 3 lesson 2 VSEPR.ppt
- 2. MELCS: • Determine if a molecule is polar or non- polar given its structure. (S11/12PS-IIIc-15)
- 3. OBJECTIVES At the end of the lesson, the students should be able to: 1.Explain VSEPR (Valence Shell Electron Pair Repulsion) theory. 2.Draw the geometry of molecules using the VSEPR theory in the Lewis dot structure. 3.Distinguish between polar and non-polar molecules.
- 4. TOPIC: Polarity of Molecules Lesson 2: Molecular Geometry: VSEPR (Valence Shell Electron Pair Repulsion)
- 8. Electronegativity refers to the extent of attraction of an atom for a shared pair of electrons.
- 10. Types of Covalent Bond Polar Covalent Bond Non polar Covalent Bond
- 11. Types of covalent bonds –Non-polar covalent: equal sharing of electrons –Polar covalent: unequal sharing of electrons
- 12. EXAMPLE: HF (hydrofluoric acid) H= 2.1 Computation: 4.0 - 2.1 = 1.9 F= 4.0 Bond: Polar Covalent
- 13. EXAMPLE: Cl2 (chlorine gas)
- 16. Let’s have a warm up exercise!!!
- 17. ACTIVITY 1: What Shape is this? Directions: Identify the geometrical shapes on the following slides.
- 18. Linear
- 19. bent
- 20. tetrahedral
- 21. Trigonal planar
- 23. octahedral
- 25. seesaw
- 26. Molecular geometry - pertains to the three-dimensional arrangement of atoms in a molecule
- 27. The approach in predicting molecular GEOMETRY is through………..????
- 28. VSEPR theory Valence Shell Electron Pair Repulsion theory
- 29. 4 Key ideas of the VSEPR theory
- 30. 1st…. Electron pairs stay as far apart from each other as possible to minimize repulsions.
- 31. For example
- 32. 2nd…. Molecular shape is determined by the number of bond pairs and lone pairs around the central atom.
- 33. For example
- 34. Lone pair pair of valence electrons that are not shared with another atom in a covalent bond and is sometimes called an unshared pair or non- bonding pair. found in the outermost electron shell of atoms. can be identified by using a Lewis structure.
- 35. Bond pair A bond pair is a pair of electrons that are in a bond. A single bond is always composed of two electrons that are paired with each other. These two electrons together are called the bond pair.
- 36. For example
- 37. 3rd… Treat multiple bonds as if they were single bonds (in making the prediction).
- 38. For example
- 39. 4th… Lone pairs occupy more volume than bond pairs. Lone pair – lone pair repulsions are greater than lone pair – bond pair repulsions which in turn are greater than bond pair – bond pair repulsions.
- 40. Example of Lewis structure
- 42. NH3
- 43. To minimize repulsion, electron pairs ( bond pair and lone pair) should be oriented accordingly.
- 45. Guidelines for Applying the VSEPR Model Step 1: Draw the Lewis structure Step 2: Count the number of electron pairs around the central atom. Step 3: Use Table 2 to predict the geometry of molecule. Step 4: Determine the molecular geometry. Step 5: Draw the molecular geometry.
- 46. Example: H2O Step 1: Draw the Lewis structure
- 47. 4 electron pairs around the central atom: 2 bond pairs 2 lone pairs Step 2:Count the number of electron pairs around the central atom
- 48. Step 3. Use the table to predict geometry • The arrangement of electron pairs are tetrahedral
- 49. Step 4: Determine the molecular geometry Bent
- 50. Step 5: Draw/ assemble the molecular geometry using the ball and stick model
- 51. Let’s do this……. Activity 2: Given the task cards, determine the molecular geometry of molecules by using the ball and stick model.
- 52. Let’s do this……. 1. Draw the Lewis dot structure and follow the VSEPR in determining the molecular geometry of molecules. 2. Determine if the molecule is polar or nonpolar given its structure.
- 53. Present your molecular model to the class.
- 55. HCl Number of electron pairs of the central atom: 4 (1 bond pair and 3 lone pairs) Arrangement of electron pairs: tetrahedral Molecular Geometry (VSEPR shape): linear Geometric Sketch :
- 56. NH3 (ammonia)
- 57. NH3 Number of electron pairs of the central atom: 4 (1 lone pair and 3 bond pairs) Arrangement of electron pairs: tetrahedral Molecular Geometry (VSEPR shape): trigonal pyramidal Geometric Sketch :
- 59. SO2 Number of electron pairs of the central atom: 3 (1 lone pair and 2 bond pairs) Arrangement of electron pairs: trigonal planar Molecular Geometry (VSEPR shape): bent Geometric Sketch :
- 61. BF3 Number of electron pairs of the central atom: 3 (no lone pair) Arrangement of electron pairs: trigonal planar Molecular Geometry (VSEPR shape): trigonal planar Geometric Sketch :
- 63. CF2Cl2 Number of electron pairs of the central atom: 4 (no lone pair) Arrangement of electron pairs: tetrahedral Molecular Geometry (VSEPR shape): tetrahedral Geometric Sketch :
- 64. CH4 (methane)
- 65. CH4 Number of electron pairs of the central atom: 4(no lone pair) Arrangement of electron pairs: tetrahedral Molecular Geometry (VSEPR shape): tetrahedral Geometric Sketch :
- 66. Keep this in mind…….. VSEPR model generates realible predictions of the geometries of molecular structures. Chemists use the VSEPR approach because of its simplicity.
- 67. Keep this in mind…….. Aside from electronegativity as factor to determine the polarity of molecule, molecular geometry applying the VSEPR theory is one good way to determine whether a molecule I polar or nonpolar.
- 68. Activity 3 • Given the Lewis structure of molecules, predict the VSEPR Shape that corresponds to the structure of molecule. • Determine if the molecule is polar or nonpolar.
- 69. 1. Beryllium Dichloride (BeCl2)
- 70. 2. Water (H2O)
- 71. 3. Carbon tetrachloride (CCl4)
- 72. 4. Sulfur trioxide (SO3)
- 73. 5. Sulfur trioxide ion SO3 2-
- 74. 6. Tellurium hexafluoride (TeF6)
- 75. 7. Phosphorus pentachloride (PCl5)
- 76. 1. Beryllium Dichloride (BeCl2) Polarity polar Molecular Geometry Linear
- 77. 2. WATER (H2O) Polarity POLAR Molecular Geometry Bent
- 78. 3. Carbon tetrachloride (CCl4) Polarity nonpolar Molecular Geometry tetrahedral
- 79. 4.Sulfur trioxide (SO3) Polarity nonpolar Molecular Geometry trigonal planar
- 81. 5. Sulfur trioxide ion SO3 2- Polarity polar Molecular Geometry trigonal pyramidal
- 83. 6. Tellurium hexafluoride (TeF6) Polarity nonpolar Molecular Geometry octahedral
- 84. 7. Phosphorus pentachloride (PCl5) Polarity nonpolar Molecular Geometry trigonal bipyramidal
- 85. Nonpolar molecule If the shape is symmetrical due to the equal sharing of electrons hence no dipole moment produced. The valence electrons are shared equally on both sides of the atom.
- 86. Examples: O2, F2, Cl2
- 87. Nonpolar molecule if: the central atom does not have lone pairs thus electrons were equally shared to another atom of the same element Examples: CF4 and CO2
- 90. Polar molecule If the shape is asymmetrical due to the unequal sharing of electrons creating a dipole moment. Examples: HCl, HF
- 92. Polar molecule if: The central atom or one of the central atoms has lone pair Examples: H2O and NCl3
- 94. Polar molecule if: - the central atom does not have lone pair but bonded to atoms of different kind Examples: CH2F2 (difloroumethane) and OCS (carbonyl sulfide)
- 96. Summary 1. Polarity of molecules can be determined by two ways: solving for electronegativity (from previous lesson) and determining molecular geometry using the VSEPR theory. 2. In determining molecular geometry using the VSEPR theory it is a must to illustrate the atoms Lewis dot structure. 3. Chemists use the VSEPR approach to determine a molecules polarity due to its simplicity.
- 97. Evaluation: Choose the letter that corresponds to the best answer. 1. Which of the following molecule will exhibit tetrahedral geometry? a. CCl4 b. CO3 c. O3 d. PCl5
- 98. 2. The geometry of the molecule BF3 is? a. linear b. tetrahedral c. pyramidal d. trigonal planar
- 99. 3. If there are 3 electron pairs around the central atom of a molecule, these electron pairs are in a ______? a. linear b. trigonal planar c. trigonal pyramidal d. bent
- 100. 4. Predict the geometry and polarity of the CS2 molecule. a. linear, nonpolar b. tetrahedral, polar c. linear, polar d. bent, polar
- 101. 5. Which of the following compound correctly matches with its molecular geometry? a. CO2: tetrahedral b. NH3: trigonal pyramidal c. H2O: linear d. O2: bent
- 103. Evaluation: Choose the letter that corresponds to the best answer. 1. Which of the following molecule will exhibit tetrahedral geometry? a. CCl4 b. CO3 c. O3 d. PCl5
- 104. 2. The geometry of the molecule BF3 is? a. linear b. tetrahedral c. pyramidal d. trigonal planar
- 105. 3. If there are 3 electron pairs around the central atom of a molecule, these electron pairs are in a ______? a. linear b. trigonal planar c. trigonal pyramidal d. bent
- 106. 4. Predict the geometry and polarity of the CS2 molecule. a. linear, nonpolar b. tetrahedral, polar c. linear, polar d. bent, polar
- 107. 5. Which of the following compound correctly matches with its molecular geometry? a. CO2: tetrahedral b. NH3: trigonal pyramidal c. H2O: linear d. O2: bent
- 108. Assignment Activity 5: POLARITY OF MOLECULES Direction: Complete the table with necessary information learned from Lesson 1 to Lesson 3. Use the worksheet provided for your answers.
- 113. Non-polar covalent • Sharing of electrons equally • Usually occurs when two identical atoms are bonded together. • Examples: H2, O2, N2, Cl2, Br2, I2, F2
- 114. Polar covalent • Unequal sharing of electrons • Unequal sharing caused by 2 elements with different electronegativities (different abilities to attract electrons). • The bond is called a dipole (two poles) • Creates molecule with partial charges
- 115. • Partial charges symbolized by (delta) + and - • The more electronegative atom is located at the partially negative end • Example: + - H-Cl and H-Cl
- 116. Polar molecule or not? • The shape of a molecule usually tells if a molecule is polar or not • If the VSEPR shape is symmetric it is usually non-polar • If the molecule is asymmetric it is polar
- 117. Name Polar example Non-polar example Linear HCl CO2 Trigonal Planar CH2O AlH3 Tetrahedral CH3OH CH4 Trigonal pyramidal always Bent always Youtube polar vs nonpolar