PowerPoint PresentationSlide 2Slide 3Slide 4Slide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14Slide 15Slide 16Slide 17Slide 18Slide 19Slide 20Slide 21Slide 22Slide 23Slide 24Slide 25Slide 26Slide 27Slide 28Slide 29Slide 30Slide 31Chemical BondsFormation of Compounds from atomsPreparation for College ChemistryColumbia UniversityDepartment of ChemistryTrends in the Periodic Table Trends in the Periodic Table Lewis Structures VSEPR ModelDecreases going across a period from left to right, increases going down groupAtomic and Ionic RadiiIonization EnergyX(g)X+(g) + e-Minimum energy necessary to remove an electron from a neutral gaseous atom in its ground state (IE > 0, ground state stable system)∆E = IE1X+(g)X2+(g) + e-∆E = IE2First Ionization EnergiesElectron Affinity EAElectron attachment energy. Energy released when a gaseous atom in its ground state gains a single electron.EAX(g) + e-X-(g)> 0< 0Gilbert LewisFFFFF F FF 2s2p5P 2s2p3PLewis Structures of AtomsFOFF HThe Octect RuleIn H2O and HF, as in most molecules and polyatomic ions, nonmetal atoms except H are surrounded by 8 electrons (an octet). Each atom has a noble gas electronic configuration (ns2p6 ).O FF-2s2p6Na +2s2p6NaIonic Bond. Electron Transfer+-Na+F-ClOIonic Bond. Electron TransfergClg]2+Cl-Cl-Mgg]2+O2-OAlAl]3+O2-AlOOAl]3+O2-O2-Ionicity vs. CovalencyHHHHEnergyEnergyHHHH....HHHH....bond energybond energyPotential Energy DiagramElectrostatic forces in the HElectrostatic forces in the H22 molecule moleculenuclear repulsionnuclear repulsion(destabilization)(destabilization)electron repulsionelectron repulsion(destabilization)(destabilization)electron-nuclear attractionelectron-nuclear attraction(stabilization)(stabilization)H2 Electron Configuration:Bonding and Non-Bonding OrbitalsH H1s 1sTwo s atomic orbital = Twomolecular orbital (MO)One bonding, one antibonding. Covalent Bond. Sharing e-Only bonding MO shownFFFF F FTwo p AO = TwoMOOnly bonding MO shownCollinear orbitals form  bondOFour p AO = TwoMO, and two Only bonding MO shownCoplanar orbitals form  bondOOOO OHe2 Electron ConfigurationHe He1s21s2HElectronegativityClClHLinus PaulingFFNa+Cl-HClDipole03.3ClHLewis Structures of CompoundsCount valence electrons available.number of valence electrons contributed by nonmetal atom is equal to the last digit of its group number in the periodic table. (H = 1)Add electrons to take into account negative charge.Ex.OCl– ion: 6 (O) + 7 (Cl) + 1 (charge) = 14 valence e–CH3OH molecule: 4 (C) + 4(H) + 6 (O) = 14 valence e–Lewis Structures of CompoundsDraw skeleton structure using single bondsNote that carbon almost always forms four bonds.Central atom is written first in formula.Terminal atoms are most often H, O, or a halogen.Ex. O — Cl-H — C — O— HHHLewis Structures of CompoundsSubtract two electrons for each single bondO-Cl– ion: 14 – 2 = 12 valence e-– leftCH 3OH molecule: 14 – 10 = 4 valence e- leftDistribute remaining electrons to give each atom a noble gas structure (if possible).O — Cl H — C — O — HHHLewis Structures of CompoundsToo Few Electrons?Form multiple bondsEx. What is the structure of the NO3 – ion?Skeleton:N OOOvalence e– = 5(N) + 18 (3O) + 1(charge) = 24 e– Ovalence e– left = 24 - 6 (3 single bonds) = 18 e– Adding a double bond and rearranging:N OOOResonance StructuresONOON OOOIIIIIINitrate Ion (cont.)Molecular GeometryMolecular Geometry. VSEPR1. Electron pairs (lone and bonding pairs) around a central atom tend to be oriented so as to be as far apart as possible to minimize their repulsions2. The molecular geometry is hence determined by the relative locations of the electron pairs3. The SN (Steric Number) of the central atom is used to find the geometry that applies€ SN =# atoms bonded to central atom ⎛ ⎝ ⎜ ⎞ ⎠ ⎟+# lone pairs on central atom ⎛ ⎝ ⎜ ⎞ ⎠ ⎟Molecular GeometryIn XYn molecules in which there are no lone pairs, the SN is used to predict geometryBeF2 linear (SN = 2)BF3 trigonal planar (SN = 3) CF4 tetrahedral (SN = 4) PF5 triangular bipyramid (SN = 5) SF6 octahedral (SN = 6)Molecular GeometryMoleculeLewis Str.Pairs of e-electronarrangem.MolecularShapeH2S4tetrahedralbentH S HCCl4CClClClCl4tetrahedraltetrahedralVSEPR