Chemical Bonding Why do bonds form?to lower the potential energy between positive and negative charges positive charges protons cations negative charges electrons anions metals Periodic Table lose e - non-metals gain e -

metal + non-metal Ionic bonding Groups 1 and 2Groups 6 and 7 low Ionization Energy lose 1 or 2 valence e - high Electron Affinity gain e - electron transfer takes place electrostatic attraction between cation and anion formula= ratio of anions to cations e-e- + -

+ non-metalnon-metal Covalent bonding electrons shared between atoms high Ionization Energies high Electron Affinities electron density between the atoms distance between atoms = bond length formula = actual # atoms

metal+ metal Metallic Bonding metalsvalence e - well shielded low Ionization Energy low Electron Affinities share valence e - not localized between atoms delocalized move freely throughout metal Na e - “sea” (nucleus and core e - ) (valence e - )

metal + non-metal Ionic bonding Na (s) 2 + Cl 2 (g)  NaCl (s)2 exothermicheat given off Ionization Energy Na+ 496 kJ/mol Electron AffinityCl-349 kJ/mol Lattice Energy Na + Cl - E = d -504 kJ/mol Na + + Cl - NaCl negative Coulomb’s law kQ1Q1 Q2Q2

Lewis electron-dot symbols element symbol= nucleus + core e - one “dot” =valence e- metalsdot = e - it loses to form cation non-metal unpaired dot = e - paired through e - gain or sharing

metal + non-metal Ionic bonding Na (s) 2 + Cl 2 (g)  NaCl (s)2 [Ne] [Ar] Ca O ::.... [Ar]4s 2 [He]2s 2 2p 4 Ca 2+ O 2- [Ar][Ne] Ca(s) O 2 (g)  CaO (s) Sn, Pb, Bi and Tl exceptions Na. + Cl - :: : : + Cl : : :. Na + 3s13s1 3s23p53s23p5

Ionic sizes isoelectronic series 46 e ions get smaller same # electrons + - e-e-

+ non-metalnon-metal Covalent bonding H. + H. H.. H 1s11s1 1s11s1 [He]

F. : : : : F. : : +. :: F.: : F : : [He]2s 2 2p 5 [Ne] F : : : F : : : e - not used in bonding lone pairs Lewis structure shared equally between F HO. : :.. : O :.. H. H. oxygen 2 lone pairs bonding pair 1s11s1 [He]2s 2 2p 4 [He] shared e - bonding pair not shared equally [Ne]

Electronegativity ability of an atom in a molecule to attract e - to itself related to Ionization Energy Electron Affinity Pauling scale

non-polar covalent  0.4 polar covalent NaCl2.1ionic801 o C AlCl 3 1.5polar covalent178 o C PCl polar covalent 76 o C Cl 2 0.0covalent ionic> 1.8 C H C O -- ++ Li 2 O BeCl polar covalent405 o C -101 o C