AP Chemistry Ms. Ye Name Date Block 1. Draw a Lewis structure for each of these molecules. Identify the molecular shape, hybridization, and bond angles. Determine the total number of valence electrons that need to be represented in the structure Set up your Lewis Structure by placing the atom that desires the most bonds in the middle Satisfy the HONC Rule and Octet Rule first If there are valence electrons that are not accounted for, put them on the central atom. a. SiCl4 Total Val e - = d. HOBr Total Val e -= b. PF3 Total Val e - = e. BrF5 Total Val e - = c. CS2 Total Val e - =
Resonance- Resonance structures are around the structure. Resonance occurs when electrons can flow through neighboring pi systems. In these structures, covalent bonding cannot be represented by one Lewis structure. The Examples: 1. Draw the possible resonance structures for the following covalent compounds: a. O3 b. 2. Draw all resonance forms for 3. Draw all the possible resonance structures (indicated in parentheses) for each of these molecules. a. NO3 1- (3) b. SO2 (2)
Formal Charge Assigned integer charges to each atom in a molecule Allows for the comparison of electrons "owned" by an atom in a Lewis structure versus the number of electrons possessed by the same atom in its unbound, free atomic state. h = # # ½ # OR Evaluation of Lewis structure Atoms in molecules must equal to the The best Lewis structure or resonance contributing structure has the It is preferred to have a Example: 1. Consider the Lewis structures for SO4 2-. Determine the formal charges for all atoms in each structure. Which SO4 2- structure is the most accurate? 2. Identify the formal charges on each element in these structures 3. Use formal charges to determine which resonance structure is the one that most closely resembles the real structure of the molecule indicated
Polarity of MOLECULES (the entire compound) Comparing between 2 atoms in a bond, for in the compound If there is an electronegativity difference between bonded atoms, and the molecule is then the compound is If there is an electronegativity difference between bonded atoms, and the molecule is then the compound is If there is no electronegativity difference between bonded atoms, and the molecule is then the compound is Polarity Practice: Look back at some of the Lewis Structures you drew for the molecules at the beginning of class Molecule Shape SiCl4 Is the COMPOUND completely symmetrical? Is the entire COMPOUND polar or nonpolar? PF3 CS2 HOBr BrF5 *Whether a compound is polar or nonpolar determines its molecular behavior Like dissolves like Polar substances in polar substances Nonpolar substances in nonpolar substances Polar substances in nonpolar substances
*Whether a compound is polar or nonpolar determines the types of attractive forces between its molecules Intermolecular Forces (sometimes referred to as Van der Waals forces ) These are NOT BONDS, which are an attraction 3 Main Types of Intermolecular Forces: London Dispersion Forces o The intermolecular force o Is the main attractive force between o In general, the the molecule, the the dispersion forces Dipole-Dipole Forces o Stronger than dispersion forces o The main attractive force between Hydrogen Bonding: is a type of intermolecular force; it is NOT actually a bond! o The intermolecular force o Only occur in molecules containing AND one of the following:,, or (NOF) Let s go back to the compounds we looked at on the previous page Molecule SiCl4 Is the entire compound polar or nonpolar (look at symmetry)? Does the compound contain H and either N, O, or F? Main type of intermolecular forces between molecules of this compound PF3 CS2 HOBr BrF5
Putting it all together Draw all resonance structures if it applies! Indicate shapes for multiple central atoms if it applies! H2CO POCl3 SiF4 Essential Information: 3D Lewis Structure(s). Label Bond Angles! Essential Questions: Additional Information: : N2O # sigma bonds: Geometry/Shape: Major intermolecular
Essential Information: 3D Lewis Structure(s). Label Bond Angles! Essential Questions: Additional Information: SO3 SF4 ClF3 : XeF4 # sigma bonds: Geometry/Shape: Major intermolecular