Order of Filling Subshells

Transcription

1 Bonding: General Concepts Ionic Bonds Sections Covalent Bonds Section 13.7 Covalent Bond Energy & Chemical Reactions Section Lewis Structures Sections VSEPR Theory Section Friday Week 6 CHEM Sections L and M 1 rder of Filling Subshells What is the order in which subshells are filled? 4s level filled before 3d Figure from Chemistry the Easy Way by Joseph A. Mascetta Week 6 CHEM Sections L and M 2 1

2 What is Bond Energy? Bond energy is the energy required to make or break 1 mol of a chemical bond. Energy is released when bonds are broken: Exothermic Energy is supplied when bonds are formed: Endothermic Week 6 CHEM Sections L and M 3 Bond Energies, kj/mol Higher bond energy Single bonds have lower bond energy in general Week 6 CHEM Sections L and M 4 2

3 Bond Lengths & Energies Multiple bonds are shorter than single bonds. Week 6 CHEM Sections L and M 5 What is enthalpy (H)? Enthalpy A state function: pathway does not matter H = E + PV, where E = internal energy of a system P = pressure of the system V = volume of the system Δ H = q p the energy flow as heat at constant pressure How can enthalpy help us understand chemical bonding? Week 6 CHEM Sections L and M 6 3

4 Bond Enthalpy For a chemical reaction, Δ H = Σ Energy bonds broken - Σ Energy bonds formed Bond enthalpy = Δ H in a reaction in which a chemical bond is broken in the gas phase. C 2 F 2 (g) + 2 H 2 (g) CH 2 2 (g) + 2 HF(g) What is the overall bond enthalpy for this reaction? Week 6 CHEM Sections L and M 7 Enthalpy of Reaction More energy is supplied from bond formation than that released from bond breaking. Thus, overall reaction is endothermic. Week 6 CHEM Sections L and M 8 4

5 Drawing Lewis Structures Write the Lewis structure for P 3 1. Count # of valence available - A Element Atomic # Shell ccupancy # Valence e - P SUM = (7x3) = 32 valence Week 6 CHEM Sections L and M 9 Drawing Lewis Structures Write the Lewis structure for P 3 2. Count total # of needed - N Element # e - Needed P s 24 SUM = 40 valence Week 6 CHEM Sections L and M 10 5

6 Drawing Lewis Structures Write the Lewis structure for P 3 3. Calculate # e - s shared: S = (e - Needed) - (e - Available) S = = 8 valence shared (8 shared ) P 4. Draw skeleton w/ shared e - Week 6 CHEM Sections L and M 11 Drawing Lewis Structures Write the Lewis structure for P 3 5. Assign remaining shared as double or triple bonds. (NT REQ D IN THIS EXAMPLE) P Week 6 CHEM Sections L and M 12 6

7 Drawing Lewis Structures Write the Lewis structure for P 3 6. Assign remaining as lone pairs. P Shared Lone-pair Week 6 CHEM Sections L and M 13 Drawing Lewis Structures Write the Lewis structure for P 3 7. Calculate the formal charge on each atom P Phosphorus (8) 2 # valence # lone pair # bonding Formal Charge on Phosphorus: +1 Week 6 CHEM Sections L and M 14 7

8 Drawing Lewis Structures Write the Lewis structure for P 3 7. Calculate the formal charge on each atom P Chlorine (2) 2 # valence # lone pair # bonding Formal Charge on Chlorine: 0 Week 6 CHEM Sections L and M 15 Drawing Lewis Structures Write the Lewis structure for P 3 7. Calculate the formal charge on each atom P xygen (2) 2 # valence # lone pair # bonding Formal Charge on xygen: -1 Week 6 CHEM Sections L and M 16 8

9 Drawing Lewis Structures Write the Lewis structure for P 3 7. Calculate the formal charge on each atom P Check that formal charges sum to a net charge of 0 for the molecule (+1) Phosphorus + (0) Chlorine + (-1) xygen Formal Charge on the molecule: 0 Week 6 CHEM Sections L and M 17 PRS Question What does B represent? 1. Attractive forces dominate over repulsive forces. 2. Repulsive forces dominate over attractive forces. 3. Attractive and repulsive forces roughly balance. 4. There are no repulsive or attractive forces. Week 6 CHEM Sections L and M 18 9

10 PRS Question What does B represent? 1. Attractive forces dominate over repulsive forces. 2. Repulsive forces dominate over attractive forces. 3. Attractive and repulsive forces roughly balance. 4. There are no repulsive or attractive forces. Week 6 CHEM Sections L and M 19 PRS Question What does B represent? A = in fig represents interspecies separation that is too close together. Energy is relatively high because of repulsive forces. Week 6 CHEM Sections L and M 20 10

11 PRS Question What does B represent? C = in fig represents interspecies separation that is too far apart. Energy is relatively high. Attractive forces cause the species to want to move closer together. Week 6 CHEM Sections L and M 21 PRS Question What does B represent? B = in fig represents distance at which a two species are most energetically stable. At that energy, the attractive forces and the repulsive forces counteract each other. Correct Answer: 3 Week 6 CHEM Sections L and M 22 11

12 PRS Question Which of the following bonds has the lowest enthalpy? 1. C C 2. C=C 3. C= 4. C=N Week 6 CHEM Sections L and M 23 PRS Question Which of the following bonds has the lowest enthalpy? kj/mol 1. C C C=C C= C=N 615 Because single bonds generally have lower bond energies than double bonds Week 6 CHEM Sections L and M 24 12