Relative attraction of an atom for electrons, its own and those of other atoms. Pauling Scale. Same trends as ionization energy, increases from lower left corner to the upper right corner. fluorine: . = | Chapter 2 CHEMICAL BONDS AND MOLECULAR STRUCTURE Electronegativity Relative attraction of an atom for electrons, its own and those of other atoms. Pauling Scale. Same trends as ionization energy, increases from lower left corner to the upper right corner. fluorine: . = Electronegativities of the Elements Type of Chemical Bonding Non-polar bonds: diff. EN = 0 Polar bonds: diff. EN > 0 Ionic bonds: diff. EN > Ionic Compounds Ionic Compounds NaCl; copper(II) sulfate pentahydrate (CuSO4•5H2O, blue); nickel(II) chloride hexahydrate (NiCl2•6H2O, green); potassium dichromate K2Cr2O7, orange); and cobalt(II) chloride hexahydrate (CoCl2•6H2O) Covalent Bonding: Sharing of electrons A covalent bond is formed when two atoms share one or more pairs of electrons. Covalent bonding occurs when the lectronegativity difference between elements (atoms) is zero or relatively small. Compare O-O and O=O. Is O=O expected to be stronger, weaker, or the same strength? 1875-1946 American Chemist Lewis Symbol valence shell electrons = Group A # Shell Model of the Atom Lewis Structures Octet Rule In compound formation an atom gains or loses electrons, or shares pairs of electrons, until its valence shell has eight electrons. Lewis Structures CH4 methane C2H6 ethane Multiple Covalent Bonds Double bond: 2 pairs shared Triple bond: 3 pairs shared Normally occurs between: C atoms; N atoms; O atoms; a C atom and a N, O or S atom a N atom and a O or S atom a S atom and an O atom Multiple Covalent Bonds Shape: PCl3 Lewis Electron Dot Structure :Cl : P : Cl: :Cl: 3 bond pairs 1 lone pair => AB3E trigonal pyramidal shape Shape: IF5 Lewis Electron Dot Structure : F : : F : : I : F : : F : :F : 5 bonds pairs 1 lone pair => AB5E Square pyramidal shaped Shape: IF4-1 Lewis Electron Dot Structure -1 : F : : F : : I : F : : F : 4 bond pairs 2 lone pairs => AB4E2 square planar shape Shape: SO3 Lewis Electron Dot Structure : O : S : : O : : O : 3 bond pairs 0 lone pairs => AB3 trigonal planar shape What would be expected to be the shape of chloroform, CHCl3? “see-saw” square planar tetrahedral Carbon monoxide, CO and carbon dioxide, CO2, are linear molecules. Which one is the polar molecule: CO CO2 Sigma Bond σ Bond with the greatest electron density on a line connecting the atomic nuclei s-s type p-p type s-p type s-sp3 type s-sp2 type s-sp type p-sp3 type p-sp2 type p-sp type sp3 - sp3 type sp2-sp2 type sp-sp type etc., including all combinations of s, p, d, and hybrid orbitals Pi Bond π Bond with the greatest electron density above and below a line connecting the atomic nuclei p-p type Bonding in Ethylene Bonding in Acetylene Dipole-Dipole Forces London (Dispersion) Forces Hydrogen Bonds Hydrogen Bonds Water, H2O, and methane, CH4, have very similar molar masses yet the boiling point for water is approximately 200oC higher than that for methane. The higher boiling point is due to: hydrogen bonding in water polarity of water molecules both of the above none of the above
