2 Essential QuestionsHow do properties of polar and nonpolar bonds and molecules compare?How would you describe the structure of the water molecule and how does this structure affect its function?How do the properties of water depend on the arrangement of the atoms in the molecule?What are the unique properties of water?
3 Objectives Draw lewis structures of molecules Explain why resonance occurs and identify resonance structuresExplain three exceptions to the octet rule and identify molecules in which these exceptions occur
4 Octet RuleAtoms form bonds to achieve noble gas configuration = 8 electrons in each atoms valence shellException = HWhy?
5 Structural Formulas/ Lewis Structures Shows relative position of atoms as well as number of bonds
6 Procedures1. Add up the total number of valence electrons for all the atoms. Account for charge: If a species has a negative charge (-) add one valence electron for each charge. If a species has a positive charge (+) subtract one electron for each positive chargeEx.: PH3 1xP = 5 e- 3xH = 3 e-Total: 8 valence electrons
7 Procedures2. Draw the molecular skeleton and connect the atoms with one bond. The central atom is generally the atom with the lowest electronegativity, but never HPH3
8 Procedure3. Satisfy the octet rule. Distribute the remaining valence electrons by adding lone pairs to complete the octets of the outer atoms first (H only requires two valence electrons), then place any remaining electrons on the central atom.PH3
9 Procedure4. If there are too few valence electrons to give each atom an octet, multiple bonds may be required. In this case convert outer atom lone pairs to bond pairs to form multiple bonds
13 Exceptions to Octet Only a Rule of Thumb Atoms without octets BF3 Could satisfy with double bond but experimental evidence shows only single bonds which takes precedenceAtoms with more than an octetXeF4PCl5These are possible because of bonding d orbitalsCalled Expanded Octet
14 Molecular Shape Objectives Discuss the VSEPR bonding theoryPredict the shape of and the bond angles in a moleculeDefine hybridization
15 Molecular ShapeThe shape of the molecule effects how it reacts with other moleculesUse VSEPR model – Valence Shell Electron Repulsion modelElectron pairs repel each other resulting in fixed bond anglesLone electron pairs - occupy larger orbitals – bonded pairs pushed together slightly by lone pairs
17 Electronegativity and Polarity Objectives Describe how electronegativity is used to determine bond typeCompare and contrast polar and nonpolar covalent bonds and polar and nonpolar moleculesDescribe the characteristics of compounds that are covalently bonded and compare and contrast them to ionic compounds
25 Polarity Rules Determining Polarity Is it polar? There are three ways to go about determining whether a molecule is polar or not.A. If the molecule has a net dipole, then it is polar. B. If the structure is symmetric, then it is non-polar C. There are three rules to this part: 1. When there are no lone pairs on the center atom, then the molecule is non-polar 2. If it is linear or square planar, then it is non-polar. (This rule is more important than rule 1, so it overrules it because it has lone pairs.) 3. If it has different terminal atoms, then it is polar. (This rule overrules rule 1 and 2 because it is more important.)
26 Determine whether the following molecules are polar or nonpolar SCl2H2SCF4CS2