CHAPTER 7

1. CHAPTER 7 Bonding 7.3 Molecular Geometry and Lewis Dot Structures

2. Each water molecule contains one oxygen atom and two hydrogen atoms. One central oxygen atom One hydrogen atom on either side

3. Each water molecule contains one oxygen atom and two hydrogen atoms. One central oxygen atom Why can’t a water molecule be like this? One hydrogen atom on either side

4. The oxygen forms one bond One hydrogen forms two bonds One hydrogen forms one bond The Lewis structures indicate that it is not possible Why can’t a water molecule be like this?

5. Lewis structures for individual atoms are like puzzle pieces. Put them together to form molecules.

6. Use Lewis structures to predict: 1) the chemical formula The chemical formula for water is H2O (2 hydrogen atoms for every 1 oxygen atom)

7. Use Lewis structures to predict: 1) the chemical formula 2) the bonding pattern Oxygen must be the central atom

8. Use Lewis structures to predict: 1) the chemical formula 2) the bonding pattern 3) the shape of the molecule H2O is flat and bent

9. Use Lewis structures to predict: 1) the chemical formula 2) the bonding pattern 3) the shape of the molecule To be discussed later in this section H2O is flat and bent

10. Consider the chemical formula C2H6O Does this look right?

11. Consider the chemical formula C2H6O Ethanol

12. Consider the chemical formula C2H6O Could this be right too?

13. Consider the chemical formula C2H6O Dimethyl ether

14. Two isomers of C2H6O Ethanol Dimethyl ether isomer: a specific structure of a molecule, only used when a chemical formula could represent more than one molecule.

15. Give three isomers for the formula C3H8O. Show the Lewis dot diagram and the structural formula for each molecule.

16. Give three isomers for the formula C3H8O. Show the Lewis dot diagram and the structural formula for each molecule. Asked:The Lewis dot diagrams and structural formulas for the three molecules represented by the formula C3H8O Given: Carbon has four unpaired electrons, hydrogen has one, and oxygen has two. Three carbons, eight hydrogens and one oxygen form each molecule. Relationships: The atoms will bond together such that all unpaired electrons will be paired up with electrons from other atoms.

17. Give three isomers for the formula C3H8O. Show the Lewis dot diagram and the structural formula for each molecule. Asked: The Lewis dot diagrams and structural formulas for the three molecules represented by the formula C3H8O Given: Carbon has four unpaired electrons, hydrogen has one, and oxygen has two. Three carbons, eight hydrogens and one oxygen form each molecule. Relationships: The atoms will bond together such that all unpaired electrons will be paired up with electrons from other atoms. Solve:

18. Multiple bonds Sharing a pair of electrons is called a single bond. Carbon, nitrogen and oxygen commonly form double and triple bonds. Double bond (2 pairs of electrons) Triple bond (3 pairs of electrons) Ethene Ethyne

19. Acetonitrile (C2H3N) Bond atoms together, forming single bonds.

20. Acetonitrile (C2H3N) Bond atoms together, forming single bonds. Form double bonds by bringing together single electrons from atoms that are already bonded.

21. Acetonitrile (C2H3N) Bond atoms together, forming single bonds. Form double bonds by bringing together single electrons from atoms that are already bonded. Form triple bonds with any remaining single electrons.

22. Acetonitrile (C2H3N) Bond atoms together, forming single bonds. Form double bonds by bringing together single electrons from atoms that are already bonded. Form triple bonds with any remaining single electrons. Write final Lewis dot structure and structural formula.

23. Formaldehyde (CH2O) Bond atoms together, forming single bonds.

24. Formaldehyde (CH2O) Bond atoms together, forming single bonds. Form double bonds by bringing together single electrons from atoms that are already bonded.

25. Formaldehyde (CH2O) Bond atoms together, forming single bonds. Form double bonds by bringing together single electrons from atoms that are already bonded. Form triple bonds with any remaining single electrons. Write final Lewis dot structure and structural formula.

26. Use Lewis structures to predict: 1) the chemical formula 2) the bonding pattern 3) the shape of the molecule To be discussed later in this section H2O is flat and bent

27. Valence Shell Electron Pair Repulsion H2O is flat and bent The lone pairs of electrons are not involved in bonding, but affect the shape of the molecule.

28. Valence Shell Electron Pair Repulsion H2O is flat and bent VSEPR: a theory that states that the shapes of molecules are dictated, in part, by the repulsion of the shared electrons and the unshared pairs of electrons.

29. Similar charges repel each other. Identify regions of electron density to predict the molecular geometry. 2 REGIONS Carbon dioxide

30. Similar charges repel each other. Identify regions of electron density to predict the molecular geometry. 2 REGIONS 3 REGIONS Carbon dioxide Formaldehyde

31. Similar charges repel each other. Identify regions of electron density to predict the molecular geometry. 2 REGIONS 3 REGIONS 4 REGIONS Carbon dioxide Formaldehyde Methane

32. Two regions Two areas of electron density repel to form linear shapes Two charged balloons repel in opposite directions

33. Two regions Two areas of electron density repel to form linear shapes Two charged balloons repel in opposite directions These two regions of electron density repel each other, forming a 180o angle

34. Two regions Two areas of electron density repel to form linear shapes Two charged balloons repel in opposite directions These two regions of electron density repel each other, forming a 180o angle

35. Two regions Two areas of electron density repel to form linear shapes The two 180o angles formed around each carbon make the entire molecule straight.

36. Two regions There are two isomers for the formula C3H4. Show the Lewis dot diagram for each molecule, and indicate which atoms are at the center of a linear part of the molecules.

37. Two regions There are two isomers for the formula C3H4. Show the Lewis dot diagram for each molecule, and indicate which atoms are at the center of a linear part of the molecules. Asked: The linear parts of each isomer of C3H4 Given: There are two different isomers. Part of each molecule will be linear. The molecules are made from three carbons and four hydrogens. Relationships: Each atom that has two regions of electron density around it will form a linear part of the molecule.

38. Two regions There are two isomers for the formula C3H4. Show the Lewis dot diagram for each molecule, and indicate which atoms are at the center of a linear part of the molecules. Asked: The linear parts of each isomer of C3H4 Given: There are two different isomers. Part of each molecule will be linear. The molecules are made from three carbons and four hydrogens. Relationships: Each atom that has two regions of electron density around it will form a linear part of the molecule. Solve:

39. Three regions Three areas of electron density repel to form trigonal planar shapes Three charged balloons repel into the corners of a triangle

40. Three regions Three areas of electron density repel to form trigonal planar shapes Three charged balloons repel into the corners of a triangle These three regions of electron density repel, forming 120o angles between the three atoms bonded to each carbon atom

41. Three regions Three areas of electron density repel to form trigonal planar shapes Three charged balloons repel into the corners of a triangle These three regions of electron density repel, forming 120o angles between the three atoms bonded to each carbon atom

42. Three regions Three areas of electron density repel to form trigonal planar shapes These three regions of electron density repel, forming 120o angles between the three atoms bonded to each carbon atom

43. Three regions Acetic acid when mixed with water is commonly known as vinegar and has the formula C2H4O2. The correct isomer has both oxygens bonded to the same carbon. Draw the Lewis dot structure for this isomer and indicate where the molecule will be trigonal planar.

44. Three regions Acetic acid when mixed with water is commonly known as vinegar and has the formula C2H4O2. The correct isomer has both oxygens bonded to the same carbon. Draw the Lewis dot structure for this isomer and indicate where the molecule will be trigonal planar. Asked:The trigonal planar parts of acetic acid Given: The formula for acetic acid is C3H4O2 and both oxygens are bonded to the same carbon. Relationships: Each atom that has three regions of electron density around it will form a trigonal planar part of the molecule.

45. Three regions Acetic acid when mixed with water is commonly known as vinegar and has the formula C2H4O2. The correct isomer has both oxygens bonded to the same carbon. Draw the Lewis dot structure for this isomer and indicate where the molecule will be trigonal planar. Asked: The trigonal planar parts of acetic acid Given: The formula for acetic acid is C3H4O2 and both oxygens are bonded to the same carbon. Relationships: Each atom that has three regions of electron density around it will form a trigonal planar part of the molecule. Solve:

46. Four regions The four regions of electron density around the carbon repel, forming angles of 109.5o. Four charged balloon repel into the corners of a tetrahedron, rather than lying flat in a plane

47. Four regions The four regions of electron density around the carbon repel, forming angles of 109.5o.

48. Four regions Lone pairs of electrons repel just like shared pairs Lone pair of electrons Ammonia (NH3) forms a trigonal pyramidal shape The lone pair of electrons repels the shared electrons in the H–N bonds, pushing the hydrogens away from the lone pair

49. Four regions Different geometries formed by atoms with four regions of electron density Tetrahedral Trigonal pyramidal Bent

50. What shapes are formed within the isomer of C4H5NO, which has a triple bond connecting nitrogen?