14.1 Shapes of Molecules and Ions Remember that a negative charge centers refers to the number of pairs electrons around the central atom. This includes both the lone (non bonding pairs) pairs and bonded pairs of electrons in single, double or triple bonds. Each double and triple bond counts as one negative charge center. The shape according to VSEPR theory results in five basic shapes for 5 and 6 negative charge centered molecules and ions. The overall shape depends on the number of bonding and lone pairs of electrons around the central atom. The overall bond angle is the angle between the bonded atoms attached to the central atom. To determine the overall shape and bond angle using VSEPR theory the number of bonding and lone pairs of electrons around the central atom needs to first be determined. Number of negative charge centers Number bonding pairs of electrons Number of lone / nonbonding pairs of electrons Overall Shape (according to VSEPR) Bond Angle between attached atoms (according to VSEPR) Examples 6 6 0 Octahedral 90° SF6 5 5 0 Trigonal bipyramid 90° & 120° PF5 6 4 2 Square planar 90° XeF4 1 2D Structural formula drawn in shape with angles between attached atoms 5 3 2 T-shape ∼180° & ∼90° ICl3 6 5 1 Square pyramid ~88° BrF5 5 4 1 Saw horse 90° & ∼120° SF4 5 2 3 Linear 180° XeF2 As with other molecules and ion, according to VSEPR theory the lone pairs and bonding pairs of electrons are arranged around the central atom so as to minimize the repulsion between the lone and bonding pairs of electrons. The relative magnitude of the electron pair repulsions is: Lone pair - lone pair > bonded pair - lone pair > bonded pair - bonded pair repulsion 2 Formula Lewis dot and cross diagram Structural formula (drawn in the correct shape) Number negative charge centers # Bonding pairs earound central atom BrF3 PF5 SCl4 SF6 XeF4 BrF5 PCl6- SF4 3 # lone pairs of e- around central atom Bond Angle (according to VSPR) Overall Shape (according to VSPR) Polar or non polar covalent ANSWERS Formula Lewis dot and cross diagram Structural formula drawn in the correct shape Number negative charge centers Number of bonding pairs of electrons around central atom Number of lone pairs of electrons around central atom Bond Angle (according to VSPR) Overall Shape (according to VSPR) Polar or non polar Polar or non polar BrF3 Non Polar, Symmetrical PF5 SCl4 SF6 XeF4 BrF5 4 PCl6- SF4 5