1. Covalent Bonding
Chemistry
Lesson #1

2. Sections 8.1, 8.2, 9.3, and *8.4* Sections 6.1 16.1, 6.5 and *16.3*

3. Remember… Ionic bonds form between…
An ionic bond happens when one atom… and the other atom…

4. Remember… The definition of ionic bond is…
The chemical formula of an ionic compound represents a…

5. Covalent Bonds
The four sentences above represent four of the most essential differences between covalent and ionic compounds.
These differences are so important that…

6. Essay Question!
Define ionic bond and covalent bond. Outline and define, in detail, four major differences between ionic compounds and molecular (covalent) compounds.

7. Molecular Compounds Formed by covalent bonds
Ionic compounds are generally crystalline solids at room temperature.
Molecular compounds (CO2 and water, for example, have VERY different properties.)

8. Molecular Compounds
Molecular compounds are formed through covalent bonds.
Covalent bonds are created when atoms SHARE electrons, instead of gaining and losing them.

9. Vocabulary Molecule: group of atoms joined by covalent bonds
Diatomic molecules: molecules consisting of two atoms
Molecular formula: shows how many atoms of each element a molecule contains

10. Think About It…
Chlorine is a diatomic element, meaning that it exists in its atomic state as two bonded atoms.
Draw two chlorine atoms.
Is the bond between these two atoms ionic or covalent? How do you know?

11. Properties of Molecular Compounds
Covalent bonds usually occur between…
Often are gases or liquids at room temperature
Images will show atoms “stuck” to one another

12. Properties of Molecular Compounds
In general, melting and boiling points of molecular compounds are lower than ionic compounds

13. Molecular Formulas
Molecular formula of a molecular compound shows how many atoms of each element are in ONE MOLECULE of the compound.
(Contrast this with the chemical formula of ionic compounds, which show only the ratio of elements in the compound.)

14. Molecular Formulas Example: IONIC: Calcium chloride – CaCl2
Means that in the compound there are two chloride ions for every one calcium ion
COVALENT: Carbon dioxide – CO2
Means that each carbon dioxide molecule consists of one carbon atom bonded to two oxygen atoms

15. Molecular Compounds
Molecular compounds can be significantly larger than ionic compounds.
Benzoic Acid: C7H6O2
2,4-Dichlorophenoxyacetic acid: C8H6Cl2O3

16. Molecular Compounds Formulas not always in lowest terms
Example: Ethane C2H6
Formulas do not give molecule’s structure. (It must be inferred.)

17. Structural Diagrams Molecular Formula Structural Formula
Ball-and-stick model
Space Filling Model
Perspective drawing

18. Forming Covalent Bonds
Chemistry
Lesson #1

19. Octet Rule
In covalent bonds, atoms share electrons so that they fill their valence levels
Usually 8 (but only 2 for hydrogen)

20. Single Covalent Bonds
Atoms held together by sharing one pair of electrons are said to form a SINGLE COVALENT BOND
Each atom donates one electron to the bond

21. Single Covalent Bonds Cl Cl Cl Cl

22. Single Covalent Bonds Cl Cl Cl Cl

23. Single Covalent Bonds
Single Bond Cl Cl Cl Cl
Lone Pairs

24. Covalent Bonds
Electrons that do not take part in the bond are called “lone pairs” or “unshared pairs”

25. Covalent Bonds There are exceptions!
Different elements can form different numbers of bonds
Group 7A elements need one more electron, and can form one bond
Group 6A elements need two more electrons and can form two bonds
Group 5A – three bonds
Group 4A – four bonds
Hydrogen, too!

26. Working With Covalent Bonds
Draw the electron dot structures.
Determine arrangement.
Replace shared pairs of electrons with a line. (Leave lone pairs.)

27. Draw Structural Formulas
NH3
H2S
PBr3

28. Draw Structural Formulas
H2O
CH4
OF2

29. Draw Structural Formulas
SCl2
N2H4
CCl4
CHCl3
C2H6 HF
Usually, the atom that can form MORE bonds will be in the center of the molecule!

30. Draw Structural Formulas, Part 2
CHBr3
C2Cl6
HCl
OBr2
P2H4
CI4
Usually, the atom that can form MORE bonds will be in the center of the molecule!

31. Double and Triple Bonds
Chemistry
Lesson #3

32. Double Covalent Bonds
Atoms attain noble gas configuration by sharing two pairs of electrons (four)
Bond length is shorter

33. O O Double Covalent Bonds Oxygen has 6 valence electrons
O (Group 6A) can form two bonds O O

34. O O Double Covalent Bonds Oxygen has 6 valence electrons
O (Group 6A) can form two bonds O O

35. Double Covalent Bonds
OCTET RULE NOT FULFILLED! O O

36. Double Covalent Bonds
OCTET RULE NOT FULFILLED! O O

37. Double Covalent Bonds
OCTET RULE FULFILLED! O O

38. Other molecules with double covalent bonds are…
Ethene, C2H4
Carbonyl, COH2

39. Double Covalent Bonds
When counting number of valence electrons, double bonds count as 4 shared electrons.
Hydrogen will not form double covalent bonds… why?

40. Triple Covalent Bonds
Atoms attain noble gas configuration by sharing three pairs of electrons (six)
Bond length is even shorter

41. N N Triple Covalent Bonds Nitrogen has 5 valence electrons
N (Group 5A) can form three bonds N N

42. N N Triple Covalent Bonds Nitrogen has 5 valence electrons
N (Group 5A) can form three bonds N N

43. Triple Covalent Bonds
OCTET RULE NOT FULFILLED! N N

44. Triple Covalent Bonds
OCTET RULE NOT FULFILLED! N N

45. Triple Covalent Bonds
OCTET RULE NOT FULFILLED! N N

46. Triple Covalent Bonds
OCTET RULE NOT FULFILLED! N N

47. Triple Covalent Bonds
OCTET RULE FULFILLED! N N

48. Other molecules with triple covalent bonds are…
Acetylene, C2H2
Hydrogen Cyanide, HCN
Propyne, C3H4

49. Triple Covalent Bonds
When counting number of valence electrons, triple bonds count as 6 shared electrons.

50. Diatomic Elements
Chemistry
Lesson #4

51. Diatomic Elements
Diatomic elements exist in their atomic forms as binary molecular compounds, since covalent bonds form between the atoms
i.e. a “molecule” of oxygen gas is O2, not O

52. Diatomic Elements F2
Cl2
Br2 I2 H2 N2 O2

53. Exceptions To The Octet Rule
Chemistry
Lesson #5

54. Exceptions
Compounds cannot satisfy the Octet Rule for all atoms if the total number of valence electrons is odd.
NO2 – total number of valence electrons is 17 O N O

55. More Exceptions…
Nonmetals in the third period and beyond can form more than 4 bonds, since they have empty d orbitals where they can “promote” or “store” extra s or p electrons.
Ex.: Phosphorus can form 5 bonds.

56. Naming Binary Molecular Compounds
Chemistry
Lesson #6

57. Naming Molecular Compounds
CO and CO2 are very different compounds
How can we distinguish them in their names?

58. Naming Molecular Compounds
Confirm that the compound is molecular, not ionic.
Name the elements in the order listed in the formula.
Add prefixes to identify the numbers of each atom in the compound.

59. Prefixes Used Mono- 1 Di- 2 Tri- 3 Tetra- 4 Penta- 5 Hexa- 6 Hepta- 7
Octa- 8
Nona- 9
Deca- 10

60. Naming Molecular Compounds
Omit the prefix “mono-” on the first element in the name.
Add “-ide” as a suffix at the end of the second element’s name.

61. Examples
N2O
Nitrogen oxygen
Dinitrogen monoxygen
DINITROGEN MONOXIDE

62. Practice: Write the Molecular Formula
Nitrogen trichloride
Carbon tetrabromide
Diphosphorus trisulfide

63. Practice: Write the Name
Cl2O8
PH3
N2O4
SF6
H2O
S2F10
PCl5
N2F6

64. Polar Bonds and Molecules
Chemistry
Lesson #7

65. Electronegativity A measure of how well an atom attracts electrons
Measured in “Paulings”
In a molecule, some atoms more forcefully attract electrons than others

66. Electronegativity Decreases from top to bottom
Increases from left to right

67. Polar Bonds
Polar bond – covalent bond in which electrons are shared UNEQUALLY
Difference in electronegativity values controls whether bond is nonpolar, polar, or ionic

68. Polar Bonds Differences: 0.0-0.6  nonpolar covalent
1.8+  ionic

70. Polar Bonds
Greek letter Delta (δ) represents the partial charge acquired by atoms in a polar bond
H2O HF
CO2

71. Intermolecular Attractions
Polar molecules attracted to one another (called dipole interactions)
Hydrogen bonds are attractions that occur between hydrogen and unshared electrons on another molecule

72. Test Review
Chemistry

73. Test Review Covalent bonds – definitions Molecular vs. ionic compounds
Writing structural formulas
Writing molecular formulas (from name or from structure)
Writing compound names
Information on Polar Bonds