2. Chapter 3 Molecules and Bonds

3. Objectives Ionic Bonding –Describe the characteristics of an ionic bond –Understand and explain the octet rule Covalent Bonding –Describe the characteristics of a covalent bond –Describe the difference between polar and nonpolar covalent bonds Naming Chemical Compounds –Write names for ionic compounds, molecular compounds, and acids

4. CHEMICAL BONDS In almost all stable chemical compounds each atom attains a ________________________. This forms the basis of our understanding of chemical bonding. Atoms are held together in a substance by strong, attractive forces called –Many types of bonds –Two major types

5. Bonding In reactions, _______ are exchanged to form new compounds __________ can be traded or stolen in the formation of those compounds Octet rule Electronegativity

6. Ionic Bonding All atoms want to be “ –Complete set of –This is for most atoms H and He need only – WHY? Elements will gain, lose, or share electrons to –Which elements will gain electrons? –Which elements will lose electrons? –Which elements might share electrons?

7. Ionic Bonding Ionic bond: the electrostatic attraction between positive and negative ions Cation – – Anion –a–a –

8. Ionic Bonds Result from one atom This is done to satisfy octet Lewis structures to show

9. Ionic Bonding Attraction between electrostatic charges is a strong force which holds atoms together Transfer of electrons from one atom to another

10. Ionic Bonding Lewis Dot Diagrams –Show –Use dots (Figure 7-9) –Move in clockwise direction (12, 3, 6, 9) with one dot in each spot before filling with pairs… Draw Lewis Structures of

11. Practice Show the electron transfer between

12. Predicting Charges of Ions Look at column –Remember the octet rule Look at

13. Predicting Formulas Math Method –Ion charges must balance to 0 – Criss-Cross Method –Ion charges must balance to 0 –

14. Stock System Look at Cu – Use Roman Numbers to show the charge –

15. Naming Use the stock system For binary ionic compounds –Name of positive (+) ion –Name of negative (-) ion

16. Polyatomic Ions Primarily negatively charged –NO 3 -1, SO 4 2- See table 3.2 p 75

17. Polyatomic Ions Naming nonmetallic elements that combine with oxygen to form more than one polyatomic ion: –Ion with smaller proportion of –Ion with large proportion of

18. Polyatomic Ions When a series of negative ions extends to 3 or 4 members prefixes are also used –ClO - = –ClO 2 - = –ClO 3 - = –ClO 4 - =

19. Are Ionic Compounds Important? TSP Bones Nerves Drugs Seasoning Preservatives Soaps Electrolytes Blood

20. The Covalent Bond A pair of electrons Most common type of bond Stronger than ionic bond Electron orbital __________ to include both nuclei –most often found between two nuclei –Negative charges allow positive nuclei to be drawn close to each other

21. The Covalent Bond Molecule: group of atoms that are Molecular Formula: –Also tells total –C 6 H 12 O 6 = Structural Formula: indicates kind, number, arrangement, and bonds of atoms in a molecule –Lewis Structures…

22. The Covalent Bond LEWIS STRUCTURES of covalent bonds –Use

23. The Covalent Bond Single bond: 2 electrons shared between 2 atoms Double bond: 2 pairs (4 electrons) shared between 2 atoms Triple bond: 3 pairs (6 electrons) shared between 2 atoms Multiple bonds are stronger than single bonds Multiple bonds are stronger than single bonds Harder to break Harder to break Draw Lewis structure and put “puzzle” together to know single, double, or triple bonds…

24. Bonding –Molecule: Diatomic molecule: –All but 8 elements use their atomic symbols to denote the neutral atom, its elemental state (found uncombined…_ –BUT 8 are found to be diatomic (never uncombined in nature) and are expressed as neutral elements in the following forms:

25. Naming Covalent Compounds Common names: Use

26. Naming Molecular Compounds (Covalent Bonds) Use prefixes to indicate number of atoms in molecule –Don’t use “mono” for first atom PrefixMeaningPrefixMeaning Mono1Hexa6 Di2Hepta7 Tri3Octa8 Tetra4Nona9 Penta5Deca10

27. Lewis Structures

28. Rules Choose the central atom –Usually Draw the Lewis atom Position the remaining atoms around the central atom

29. Rules Draw a line connecting –This is –Represents Remaining electrons left around the central atom

30. Showing Covalent Bonds Lewis structures –H2–H2 –

31. Multiple Central Atoms C 3 H 8

32. Multiple Bonds C 2 H 4

33. Bonding Molecular Compound: Polyatomic ions: charged group of covalently bonded atoms – –

34. Polyatomic Ions Still have to satisfy the octet rule

35. Ionic? Covalent?

36. Predicting Bonds How do you know which bond will result? –Compare Electronegativity: Atoms have different –Electrons will spend more time near atoms So…one atom assumes a partial positive charge The other assumes a partial negative charge

37. Electronegativity Electronegativity trends and periodic table –Generally –Decreases Highest is Lowest is

38. Electronegativity Polarity is determined by difference in electronegativity –Nonpolar Covalent Bond –Polar Covalent Bond ( ) One electronegativity is larger…. –Ionic Bond ( ) Electronegativity is so great that no sharing occurs Electrons are lost or gained instead…

39. Ionic, Polar, NonPolar? Look at difference in electronegativity

40. Representation of Polar Bonds Use an arrow, Use arrows for Dipole moment (book) –Electrical force causing the attraction within a polar molecule

41. Overall Polarity Examine all of the bonds within a molecule Contributes to the shape CO 2

42. Shapes…

44. VSEPR and Shape Shapes of interest –Linear –Bent –Trigonal planar –Trigonal pyramid –Tetrahedral

45. Floating… Polarity manifested in properties Compare