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Copyright Sautter 2003
MOLECULAR GEOMETRY (SHAPES)
• SHAPES OF VARIOUS MOLECULES DEPEND ON THE BONDING TYPE, ORBITAL HYBRIDIZATIONS AND THE NUMBER OF BONDS THAT OCCUR IN THE BONDING ATOMS OF THE MOLECULE.
• THREE FUNDAMENTAL RULES RELATE TO THE POSITIONING OF ATOMS IN MOLECULES.
• (1) BONDED ATOMS TEND TO MOVE AS CLOSE AS POSSIBLE TO THE CENTRAL ATOM OF A MOLECULE
• (2) ATOMS WHICH ARE BONDED TO THE CENTRAL ATOM TEND TO STAY AS FAR FROM EACHOTHER AS POSSIBLE.
• (3) LONE ELECTRON PAIRS IN A MOLECULE TEND TO REPEL OTHER LONE PAIRS AND OTHER BONDING ELECTRON PAIRS.
ELECTRONEGATIVITY VALUES OF ATOMS IN THE MOLECULE.
EN = DIFFERENCE IN ELECTRONEGATIVITY.
AS EN INCREASES, BOND POLARITY INCREASES.
ELECTRONS MOVE CLOSER TOTHE MORE ELECTRONEGATIVE
ATOM IN THE BOND.
COLUMN # AND BONDING TYPE
MOLECULAR SHAPE AND FORMULA
TELLS IF A POLAROR NONPOLARMOLECULE IS
FORMED
SHOWS MOLECULAR SHAPEAND POLARITY OF BONDS
MEANS PARTIALLY+ OR – DUE TO ELECTRON
SHIFTS IN THE BOND
FRAME FORMAT
LINEAR - LiCl
ELECTRONSTRANSFER TOCl FROM Li & LiCl IS IONIC
COLUMN I - S BONDING
ELECTRONEGATIVITIESLi = 1.0Cl = 3.0
EN = 2.0ELECTRONS TRANSFER
TO THE CHLORINE
3D IONIC CRYSTAL LATTICE
LINEAR - BeCl2
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+
-
POLAR BONDSCANCEL & BeCl2
IS A NONPOLARMOLECULE
COLUMN II - SP BONDING
ELECTRONEGATIVITIESBe = 1.5Cl = 3.0
EN = 1.5ELECTRONS SHIFT
TOWARD CHLORINE
TRIGONAL PLANAR - BCl3
(FLAT TRIANGLE)
-
+
ELECTRONEGATIVITIESB= 2.0
Cl = 3.0EN = 1.0
ELECTRONS SHIFTTOWARD CHLORINE
-
-
POLAR BONDSCANCEL & BCl3
IS A NONPOLARMOLECULE
COLUMN II - SP2 BONDING
TETRAHEDRAL - CCl4
-
+
ELECTRONEGATIVITIESC = 2.5Cl = 3.0
EN = 0.5ELECTRONS SHIFT
TOWARD CHLORINE
-
-
-
POLAR BONDSCANCEL & CCl4
IS A NONPOLARMOLECULE
COLUMN IV - SP3 BONDING
PYRAMIDAL – NH3
1 LONE e-PAIR
-
+ +
+
ELECTRONEGATIVITIESH = 2.1N = 3.0
EN = 0.9ELECTRONS SHIFT
TOWARD NITROGENPOLAR BONDS
DO NOT CANCEL & NH3 IS A POLAR
MOLECULE
COLUMN V - SP3 BONDING
ANGULAR (BENT) - H2O
-
+
ELECTRONEGATIVITIESH = 2.1O = 3.5
EN = 1.4ELECTRONS SHIFTTOWARD OXYGEN
+
POLAR BONDSDO NOT
CANCEL & H2OIS A POLARMOLECULE
2 LONE e-PAIRS
COLUMN VI - SP3 BONDING
LINEAR - Cl2
ELECTRONEGATIVITIESCl = 3.0N = 3.0EN = 0
NO ELECTRON SHIFT
Cl2 HAS NO POLAR BONDS &IS A NONPOLAR
MOLECULE
COLUMN VII - SP3 BONDING
THE POLARITY OF A MOLECULE IS DETERMINEDBY THE PRESENCE OF POLAR BONDS,
MOLECULAR SHAPE AND MOLECULAR SYMMETRY
GENERALLY, ASSYMETRIC MOLECULES ARELIKELY TO BE POLAR WHILE SYMMETRICAL
MOLECULES TEND TO BE NONPOLAR
MOLECULES ARE POLAR WHEN ELECTRONSWITHIN THE MOLECULE SHIFT TOWARDS ONE
END OF THE MOLECULE MAKING THAT END NEGATIVE AND LEAVING THE OTHER
END POSITIVE
ASSYMETRIC TETRAHEDRAL - CH3Cl
+
ELECTRONEGATIVITIESH = 2.1C = 2.5Cl = 3.0
ELECTRONS SHIFTTOWARD CHLORINE
+
+
- ELECTRONS
SHIFT TOWARDSTHE MORE
ELECTRONEGATIVECl & MOLECULE
IS POLAR
COLUMN IV - SP3 BONDING
POLAR MOLECULES HAVE PROPERTIESDISTINCTLY DIFFERENT FROM NONPOLAR
MOLECULES.
POLAR MOLECULES ATTRACT EACHOTHER WELLAND HAVE HIGHER MELTING POINTS AND BOILING
POINTS AS WELL AS LOWER VAPOR PRESSURES
POLAR SOLVENTS DISSOLVE OTHER POLAR COMPOUNDS AND IONIC SUBSTANCES WELL.
NONPOLAR SOLVENTS DISSOLVE OTHER NONPOLAR COMPOUNDS WELL.
COMBINATIONS OF POLAR AND NONPOLARSUBSTANCES DONOT DISSOLVE WELL
-
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INTERACTION OF POLAR MOLECULESSTRONG INTERMOLECULAR ATTRACTION
NONPOLAR MOLECULES LITTLE INTERACTION BETWEEN MOLECULES
LONDON FORCES – NONPOLAR MOLECULES
PROTONS OF ONE ATOM WEAKLY ATTRACT THE ELECTRONS OF ADJACENT ATOMS AND VISE VERSA
HeHe
He
AN EXCEPTIONALLY STRONG TYPE OF POLARMOLECULE INTERACTION IS CALLED
HYDROGEN BONDING.
HYDROGEN BONDING INVOLVES POLAR MOLECULES THAT CONTAIN F-H, O-H OR N-H BONDS.
THE STRONG SHIFT IN BONDING ELECTRON PAIRSBETWEEN THESE ATOMS GIVES A VERY HIGH DEGREE OF BOND POLARITY AND GREATLY
INCREASES THE DIPOLE NATURE OF THE MOLECULE.
HYDROGEN BONDING IN H2O= HYDROGEN BONDING
STRONG COHESIVE FORCES
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