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CHEMISTRY 161 Chapter 10 Chemical Bonding II www.chem.hawaii.edu/Bil301/welcome.html. PREDICTING THE GEOMETRY OF MOLECULES. H. O. H. 1. derive Lewis structure of the molecule. 2. discriminate between bonding and non-bonding electron pairs. 3. VALENCE SHELL ELECTRON PAIR REPULSION.
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CHEMISTRY 161 Chapter 10 Chemical Bonding II www.chem.hawaii.edu/Bil301/welcome.html
PREDICTING THE GEOMETRY OF MOLECULES H O H 1. derive Lewis structure of the molecule 2. discriminate between bonding and non-bonding electron pairs 3. VALENCE SHELL ELECTRON PAIR REPULSION
VALENCE SHELL ELECTRON PAIR REPULSION VSEPR 1. identify in a compound the central atom 2. electrons repel each other 3. valence electron pairs stay as far apart as possible 4. non-bonding electrons repel more than bonding electrons
central atom non-bonding pairs no non-bonding pairs
AB2 BeCl2 Be Cl Cl TWO ELECTRON PAIRS AROUND BERYLLIUM ATOM
Cl Be Cl 180° 270° Be Be 90° 180° LINEAR ARRANGEMENT BEST IT PUTS ELECTRON PAIRS FURTHEST APART
AB3 BF3 F F B F THREE ELECTRON PAIRS AROUND THE BORON ATOM
F F B F 120° 120° B 120° THREE ELECTRON PAIRS AROUND THE BORON ATOM TRIGONAL PLANAR ARRANGEMENT BEST
B MOLECULAR SHAPE F F F THE SHAPE OF BF3 IS TRIGONAL PLANAR.
AB4 H H C H H 90° 90° C 90° 90° CH4 four electron pairs expect square planar
C better arrangement for four electron pairs TETRAHEDRAL 109.5° bigger than 90 ° in square planar tetrahedral 4 electron pairs put on the H-atoms
C C TETRAHEDRAL H 109.5° H H H shape of CH4 is tetrahedral
AB5 F F F P F F P PF5 FIVE ELECTRON PAIRS AROUND PHOSPHORUS 5 electron pairs trigonal bipyramidal
Bond angle F 900 F P F P F 1200 F shape of PF5 is trigonal bipyramidal two of the F atoms different from the others
AXIAL Bond angle F 900 F F P F 1200 EQUATORIAL F
AB6 SF6 six electron pairs around the sulfur atom F F F S S F F F octahedral 6 electron pairs
900 F F F S S F F F shape of SF6 is octahedral
central atom non-bonding pairs no non-bonding pairs
AB2E AB3 SeO2 O Se O
O Se O Se VSEPR treats double bonds like a single bond THREE ELECTRON PAIRS AROUND SELENIUM ELECTRON PAIR GEOMETRY TRIGONAL PLANAR
Se Se O O ADD OXYGENS SeO2 IS V-SHAPED (OR BENT) THE MOLECULAR SHAPE IS THE POSITION OF THE ATOMS
AB3E AB4 H N H NH3 H electron pairs around the nitrogen atom
N H N H NH3 H PUT ON THE 3 H ATOMS N H H H NH3 is trigonal pyramidal
AB2E2 AB4 four electron pairs around the oxygen atom H O H PUT ON THE 2 H-ATOMS O O H H shape of H2O is V-shaped or bent
S AB4E AB5 SF4 F F F S F TRIGONAL BIPYRAMID
F F F S F S F F F F WHERE DOES LONE PAIR GO? OR lone pairs occupy the trigonal plane (the “equator”) to minimize the number of 90° repulsions
AB4E AB3E2 AB2E3 SF4 1 lone pair See-saw shaped ClF3 2 lone pairs T-shaped XeF2 3 lone pairs Linear F F F F Xe S Cl F F F F F F lone pairs occupy the trigonal plane (the “equator”) first to minimize the number of 90° repulsions
AB5E F F F Br F F Br AB6 BrF5 Square pyramidal
AB6 AB4E2 F F F Xe F F : F Xe Xe F : F F Xe F F F XeF4 lone pairs MUST BE AT 1800
Summary of Molecular Shapes Total valence electron pairs Electron Pair Geometry Lone electron pairs Shape of Molecule 2 Linear 0 Linear 0 Trigonal planar Trigonal planar 3 1 V-shaped 0 Tetrahedral 4 Tetrahedral 1 Trigonal pyramid 2 V-shaped
Total valence electron pairs Electron Pair Geometry Lone electron pairs Shape of Molecule 0 Trig. bipyramid. 1 See-saw Trigonal bipyramidal 5 2 T-shaped 3 Linear 0 Octahedral 6 Octahedral 1 Square pyramid 2 Square planar
POLYATOMICS molecules with no single central atom we apply our VSEPR rules to each atom in the chain Example: ETHANOL
H H H C C O H H H ETHANOL C2H5OH The atoms around the carbons form a. tetrahedral arrangement The atoms around the oxygen form a V-shaped structure.
H O H H C C H H H
EXAMPLES BF4- ICl4- Cl2O SO2Cl2 Cl2CO Cl2SO N2F2 NH4+ NH2OH
Homework Chapter 10 pages 367-377, problem sets