Chem 1211 1st Edition Lecture 22 Outline of Last Lecture I Lewis Dot Structures Outline of Current Lecture I Octet Rule II Geometry III Electronegativity Current Lecture I II Octet Rule a ConcepTest How many lone pair electrons on the central atom single bonds double bonds and triple bonds respectively appear in the Lewis structure of PF6 i 0 3 3 0 ii 0 6 0 0 iii 1 3 3 0 iv 1 6 0 0 v 2 6 0 0 1 ANSWER 0 6 0 0 2 REASONING Phosphorus forms a single bond with each of the 6 fluorines Geometry a What is the geometry for AlCl3 i Octahedral ii Trigonal bipyramidal iii Tetrahedral iv Trigonal planar v Linear 1 ANSWER Trigonal planar These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute III b Electron pair geometry and molecular geometry c VSEPR valence shell electron pair repulsion i Pairs of e occupy space 1 Bonding and nonbonding ii Molecular Geometry Shapes 1 Linear one main element and 2 others 180 degrees 2 Trigonal planar one main element and 3 others flat 120 degrees 3 Tetrahedral one main element and 4 others 4 Trigonal bipyramidal one main element and 5 others 120 degrees and 90 degrees 5 Octahedral one main element and 6 others 60 degrees iii ConcepTest What are the electron pair and molecular geometries for PCl3 1 Answer tetrahedron trigonal pyramid 2 Reasoning Start with the Lewis structure of PCl3 Phosphorus has 5 electrons and each of the chorines has 7 so phosphorus will make 3 single bonds with each of the chlorines iv Electron Pair Geometry 1 4 pairs of electrons a Tetrahedral 4 bond pairs no lone pairs ex CH4 b Trigonal pyramidal 3 bond pairs 1 lone pair ex NH3 c Bent 2 bond pairs 2 lone pairs H2O 2 5 pairs of electrons a Trigonal bipyramidal 5 bond pairs no lone pairs b Seesaw 4 bond pairs 1 lone pair c T shaped 3 bond pairs 2 lone pairs d Linear 2 bond pairs 3 lone pairs 3 6 electron pairs a Octahedral 6 bond pairs 0 lone pairs b Square pyramidal 5 bond pairs 1 lone pair c Square planar 4 bond pairs 2 lone pairs d Share e between atom making molecules i Simplest model Lewis ii Shapes geometries iii Bond moleclular properties Electronegativity a Electronegativity increases as you move from left to right and as you move from bottom to top across the periodic table b ConcepTest Which pair has the higher electronegativity listed FIRST i B C ii C N iii N O iv Cl S 1 ANSWER Cl S 2 Reasoning Follow periodic table trends c The electronegativity of A and B i If it is less than 5 it is a covalent bond equal sharing ii If it is between 7 and 1 8 it is a polar covalent iii If it is greater than 2 0 it is an ionic bond
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