A Valence Shell Electron Pair Repulsion Electron pairs

� A. Valence Shell Electron Pair Repulsion Electron pairs are repelling one another and this is why molecules have specific shapes that they form.

� Linear: when there are only two atoms or the center atom is surrounded by two atoms and has no lone pair. (180˚ bond angles) �Ex. CO 2 and O 2

� Trigonal Planar: when one atom is surrounded by three others and has no lone pair. (120˚ bond angles) �Ex. BH 3

� Trigonal Pyramidal: when the center atom is surrounded by three atoms and one lone pair. (107˚ bond angles) �Ex. NH 3

� Tetrahedral: when center atom is surrounded by four atoms and no lone pairs. (109. 5˚ bond angles) �Ex. CH 4

� Bent: when center atom is surrounded by two atoms and two lone pairs. (105˚ bond angles) �Ex. � (aka H 2 O Mickey Mouse Molecule, can you see why? )

� Electronegativity: Ability of an atom in molecule to attract electrons. � If the bond has one atom that is more electronegative than another, unequal sharing of electrons! consult electronegativity chart � subtract electronegativity values from chart � classify bond: �

Subtraction Value Bond Classification 0. 0 - 0. 4 Non-polar covalent (NPC) 0. 5 - 1. 7 Polar covalent (PC) 1. 8 - 4. 0 Ionic (I) � Non-polar: equal sharing of electrons � Polar: unequal sharing of electrons � Ionic: no sharing of electrons

� Polarity: results from having one positive and one negative part in a molecule (Polar Covalents). � More electronegative atom is partially negative, less electronegative atom is partially positive

� Polar bonds can be overall polar molecules if the molecule has a net direction of charge. � Assign vectors along the bond to assess the molecule. Molecule is � Examples: more (+) on top then on CCl 4 CHCl 3 bottom Molecule is NOT polar overall! All vectors cancel out! + -