08-Jun-2012

Knowledge Statements

1. Molecules have well defined and predictable three dimensional structures; these can be represented using a number of 2-dimensional conventions. 
2. Isomers are molecules with the same atomic formulae, but different three dimensional structures and different properties.
3. Atoms that are connected by a single (a sigma bond) can rotate relative to each other. Atoms connected by a double bond (a sigma and a pi bond) cannot rotate.
4. The electron distribution in a bond depends on the relative electronegativies of the atoms in the bond. 
5. The polarity of a molecule can be determined from the shape of the molecule and the direction of polarity of the bonds.
6. Intermolecular interactions are influenced by molecular shape and polarity.   These forces influence macroscopic properties such as melting and boiling points, and solubility.
7. Ionic bonds are one end of a spectrum of polarity of bonds. The strength of an ionic interaction can be determined from Coulombic factors such as charge and distance.
8. The relative physical properties of ionic compounds can be predicted from the factors that effect the strength of Coulombic interactions (size and charge).

Performance expectations:

• Explain why different models/representation are used to represent molecules and what information each representation can give. (1)
• Given a 3 dimensional molecular structure, generate the full range of 2-dimensional representations (e.g., electrostatic potential maps, space filling models, ball and stick models, perspective formulae, and Lewis structures ).
• Draw Lewis structures of various molecules given a molecular formula; draw the structural isomers, if any, implied by a particular molecular formula.
• When given two (or more) representations of a compound, identify which are the same and which are different.
• Explain why rotation is possible around single (sigma) bonds, but not around pi bonds and how this affects molecular properties. Identify bonds in molecules that can rotate and those that can’t..
• Use Lewis structures to deduce electron pair geometry, molecular shape and the hybridization state of an atom in a molecule.
• Predict polarity of molecules using bond polarity and molecular shape.
  Identify molecules that can participate in hydrogen bonding, explain what structural features are involved.
• Use intermolecular forces to explain physical properties of molecular compounds. Predict/rank relative melting and boiling points of given compounds
• Explain the difference between covalent and ionic bonding
• Predict the type of bond found between various atoms.
• Describe the structure of ionic compounds and use it to explain their properties, such as high mp and bp, hard, brittle.
• Explain why metals tend to form positive ions and non-metals tend to form negative ions. Predict the charge for common ions.