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 TO THE MORE ELECTRONEGATIVE ATOM IN THE BOND. COLUMN # AND BONDING TYPE MOLECULAR SHAPE AND FORMULA TELLS IF A POLAR OR NONPOLAR MOLECULE IS FORMED SHOWS MOLECULAR SHAPE AND POLARITY OF BONDS MEANS PARTIALLY + OR – DUE TO ELECTRON SHIFTS IN THE BOND FRAME FORMAT
LINEAR - LiCl ELECTRONS TRANSFER TO Cl FROM Li & LiCl IS IONIC COLUMN I - S BONDING ELECTRONEGATIVITIES Li = 1.0 Cl = 3.0 EN = 2.0 ELECTRONS TRANSFER TO THE CHLORINE
3D IONIC CRYSTAL LATTICE
LINEAR - BeCl 2 -- ++ -- POLAR BONDS CANCEL & BeCl 2 IS A NONPOLAR MOLECULE COLUMN II - SP BONDING ELECTRONEGATIVITIES Be = 1.5 Cl = 3.0 EN = 1.5 ELECTRONS SHIFT TOWARD CHLORINE
TRIGONAL PLANAR - BCl 3 (FLAT TRIANGLE) -- ++ ELECTRONEGATIVITIES B= 2.0 Cl = 3.0 EN = 1.0 ELECTRONS SHIFT TOWARD CHLORINE -- -- POLAR BONDS CANCEL & BCl 3 IS A NONPOLAR MOLECULE COLUMN II - SP 2 BONDING
TETRAHEDRAL - CCl 4 -- ++ ELECTRONEGATIVITIES C = 2.5 Cl = 3.0 EN = 0.5 ELECTRONS SHIFT TOWARD CHLORINE -- -- -- POLAR BONDS CANCEL & CCl 4 IS A NONPOLAR MOLECULE COLUMN IV - SP 3 BONDING
PYRAMIDAL – NH 3 1 LONE e- PAIR -- ++ ++ ++ ELECTRONEGATIVITIES H = 2.1 N = 3.0 EN = 0.9 ELECTRONS SHIFT TOWARD NITROGEN POLAR BONDS DO NOT CANCEL & NH 3 IS A POLAR MOLECULE COLUMN V - SP 3 BONDING
ANGULAR (BENT) - H 2 O -- ++ ELECTRONEGATIVITIES H = 2.1 O = 3.5 EN = 1.4 ELECTRONS SHIFT TOWARD OXYGEN ++ POLAR BONDS DO NOT CANCEL & H 2 O IS A POLAR MOLECULE 2 LONE e- PAIRS COLUMN VI - SP 3 BONDING
LINEAR - Cl 2 ELECTRONEGATIVITIES Cl = 3.0 N = 3.0 EN = 0 NO ELECTRON SHIFT Cl 2 HAS NO POLAR BONDS & IS A NONPOLAR MOLECULE COLUMN VII - SP 3 BONDING
THE POLARITY OF A MOLECULE IS DETERMINED BY THE PRESENCE OF POLAR BONDS, MOLECULAR SHAPE AND MOLECULAR SYMMETRY GENERALLY, ASSYMETRIC MOLECULES ARE LIKELY TO BE POLAR WHILE SYMMETRICAL MOLECULES TEND TO BE NONPOLAR MOLECULES ARE POLAR WHEN ELECTRONS WITHIN THE MOLECULE SHIFT TOWARDS ONE END OF THE MOLECULE MAKING THAT END NEGATIVE AND LEAVING THE OTHER END POSITIVE
ASSYMETRIC TETRAHEDRAL - CH 3 Cl ++ ELECTRONEGATIVITIES H = 2.1 C = 2.5 Cl = 3.0 ELECTRONS SHIFT TOWARD CHLORINE ++ ++ -- ELECTRONS SHIFT TOWARDS THE MORE ELECTRONEGATIVE Cl & MOLECULE IS POLAR COLUMN IV - SP 3 BONDING
POLAR MOLECULES HAVE PROPERTIES DISTINCTLY DIFFERENT FROM NONPOLAR MOLECULES. POLAR MOLECULES ATTRACT EACHOTHER WELL AND 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 NONPOLAR SUBSTANCES DONOT DISSOLVE WELL
-- -- -- -- -- -- -- -- ++ ++ ++ ++ ++ ++ ++ ++ INTERACTION OF POLAR MOLECULES STRONG 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 He
AN EXCEPTIONALLY STRONG TYPE OF POLAR MOLECULE 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 PAIRS BETWEEN THESE ATOMS GIVES A VERY HIGH DEGREE OF BOND POLARITY AND GREATLY INCREASES THE DIPOLE NATURE OF THE MOLECULE.
HYDROGEN BONDING IN H 2 O = HYDROGEN BONDING STRONG COHESIVE FORCES -- ++ ++ -- ++ ++ -- ++ ++ -- ++ ++ -- ++ ++ -- ++ ++