Covalent bonding occurs when atoms share valence electrons to achieve stable electron configurations. Molecules are formed when atoms bond covalently, with molecular formulas indicating the types and numbers of atoms. Lewis structures represent molecules by showing bonding pairs and unshared electron pairs. Exceptions to the octet rule include hydrogen and boron. Resonance structures are used to depict molecules that cannot be represented by a single Lewis structure.

1. Chapter 6.2Covalent bonding and molecular compounds

2. Objectives:Define molecule and molecular formula.Explain the relationships between potential energy, distance between approaching atoms, bond length, and bond energy.State the octet ruleList the six basic steps used in writing Lewis structures.Explain how to determine Lewis structures for molecules containing single bonds, multiple bonds, or both.Explain why scientists use resonance structures to represent some molecules

3. Molecular compoundsMolecule – Neutral group of atoms that are held together by covalent bondsCompose most living thingsMolecular compound–

4. Chemical compound whose simplest units are moleculesMolecular compoundsChemical formula – Indicates the relative numbers of atoms of each kind in a chemical compound by using atomic symbols and numerical subscriptsH2O CO2 C12H22O11Molecular formula –

5. Shows the types and numbers of atoms combined in a single molecule of a molecular compound

6. H2O CO2 C12H22O11

7. Diatomic molecule –

8. Molecule containing only two atoms

9. H2 O2 N2Formation of a Covalent BondNature favors bonding becausePuts atoms at lower potential energyApproaching nuclei and electrons

10. Attractedto each

11. Decrease in potential energy

12. At the same time, both nuclei and two electrons

13. repel each other

14. Increase in potential energyElectron NegativePositive NucleusPotential energy is minimized when attractive forces are equal to the repulsive forcesCharacteristics of Covalent BondBond length – The distance between two bonded atoms at their minimum potential energy, that is, the average distance between two bonded atomsBond Energy –

15. The energy required to break a chemical bond and form neutral isolated atoms

16. As the bond energy increases-

17. The bond length decreasesBond length

18. Octet RuleChemical compounds tend to form so that each atom, by gaining, losing, or sharing electrons, has an octet of electrons in its highest occupied energy level.Hydrogen is an exception because it is stable with 2 electron in outer shell.

19. The eight electrons come from the main-group energy levels being filled.

20. s2p6 totals 8 electronsBonding and octet ruleF __ __ __ __ __ 1s 2s 2pF __ __ __ __ __ 1s 2s 2pBonding electron pair in overlapping orbitalsLi __ __ 1s 2s F __ __ __ __ __ 1s 2s 2p

21. Exceptions to the Octet RuleMost main-group elementsTend to form covalent bonds according to octet ruleExceptions

22. Hydrogen – forms bonds where it is surrounded by only two electrons

23. Boron - has just 3 valence electrons, so it tends to form bonds in which it is surrounded by six electrons

24. BH3 H B H H

25. Electron-Dot NotationElectron-configuration notation in which only the valence electrons of an atom of a particular element are shown, indicated by dots placed around the elements symbolDots – valence electronsSymbol – nucleus and inner-shell electrons I7 Valence electrons53 protons73 neutrons36 inner shell electrons

26. Electron-Dot NotationFirst three rows of periodic tableGroup 1 2 13 14 15 16 17 18

27. Lewis StructuresFormulas in which atomic symbols represent nuclei and inner-shell electrons, dot-pair or dashes and dots between two atomic symbols represent electron pairs in covalent bonds, and dots adjacent to only one atomic symbol represent unshared electrons.Unshared pair ( lone pair ) –

28. Pair of electrons that is not involved in bonding and that belongs exclusively to one atom

29. Structural formula –

30. Indicates the kind, number, arrangement, and bonds but not the unshared pairs of the atoms in a molecule

31. Single Bond –

32. Covalent bond produced by the sharing of one pair of electrons between two atoms.B F B – F

33. Draw the Lewis Structure of iodomethane, CH3I1. Determine the type and number of atoms in the molecule1 C 3 H 1 I2. Write the electron-dot notation for each type of atom in the molecule C H I3. Determine the total number of valence electrons in the atoms to be combinedC 1 x 4e-= 4e-H 3 x 1e- = 3e-I 1 x 7e- = 7e- 14e-Total valence electrons

34. 4. Arrange the atoms to form a skeleton structure for the molecule. IfCarbonis present, it is the central atom. Otherwise, the least-electronegative atom is central (except for hydrogen, which is never central). Then connect the atoms by electron-pair bonds. HH C I H5. Addunshared pairs of electrons so that each hydrogen atom shares a pair of electrons and each other nonmetal is surrounded by eight electrons HH C I H6. Count the electrons in the structure to be sure that the number of valence electrons used equals the number available. Be sure the central atom and other atoms besides hydrogen have an octet.14 e- so this is correct!!!

35. Multiple Covalent BondsDouble bond –Covalent bond produced by the sharing of two pairs of electrons between two atomsH H C CH HH H C CH HORTriple bond –

36. Covalent bond produced by the sharing of three pairs of electrons between two atoms N N N NOR

37. Draw the Lewis Structure for methanal, CH2O, which is also known as formaldehyde.1. Determine the type and number of atoms in the molecule1 C 2 H 1 O2. Write the electron-dot notation for each type of atom in the molecule C H O3. Determine the total number of valence electrons in the atoms to be combinedC 1 x 4e-= 4e-H 2 x 1e- = 2e-O 1 x 6e- = 6e- 12e-

38. 4. Arrange the atoms to form a skeleton structure for the molecule. IfCarbonis present, it is the central atom. Otherwise, the least-electronegative atom is central (except for hydrogen, which is never central). Then connect the atoms by electron-pair bonds. HH C O5. Addunshared pairs of electrons so that each hydrogen atom shares a pair of electrons and each other nonmetal is surrounded by eight electrons HH C O6. Count the electrons in the structure to be sure that the number of valence electrons used equals the number available. Be sure the central atom and other atoms besides hydrogen have an octet. HH C O HH C OOR14 e- = 12 e-SO

39. Resonance StructuresBonding in molecules or ion that cannot be correctly represented by a single Lewis structure.O O OO O OOr