08-Jun-2012

Knowledge Statements

1. Most of the atoms in the Universe were created in the “Big Bang”.  More complex atoms were created by fusion of lighter atoms in the centers of stars.
2. When atom of hydrogen get close to each other their interactions (bonding) are governed by the forces of attraction and repulsion that are described by Coulomb’s Law.  The most stable distance is where the force of attraction between the nuclei and electrons of each atom are maximized and the repulsions are minimized.
3. The macroscopic properties of matter arise through the properties of, and interactions between large numbers of atoms or molecules.
4. Molecules display emergent properties that are more than, and different from, the sum of their component atoms.
5. Ensembles of molecules also influence properties.
6. Atoms within molecules or networks are held together by interactions that we call chemical bonds; these can be described by a number of different bonding models. For example metals are usually described by models that explain why they conduct electricity, while the bonding models for diamond explain the strength of the material and other properties of diamond, for example the fact that they do not conduct electricity.
7. Energy is released to the surroundings when a bond forms, and external energy (from the surroundings) is required to break a bond.
8. When a bond forms, atomic orbitals are transformed into bonding orbitals; these "come into existence" only as bonds are formed. Geometric considerations are involved in their relative stabilities and so influence molecular shape.

Performance expectations:

• Describe the chain of events that produced the iron atoms in your blood; create a model and indicate when various elements arose. (1)
• Explain why atoms are (generally), stable and do not undergo fusion (the merging of atoms) outside of extreme environments.(1)
• Construct a model (draw a representation) to illustrate the differences between nuclear and chemical reactions. (1)
• Explain why atoms don’t have macroscopic properties like melting point, boiling point, and color, while macroscopic materials do (and can be identified by them). (2,3)
• Explain how physical properties like melting or boiling point are related to, and predicted from, molecular structure and intermolecular interactions (3)
• Draw a molecular level picture of what happens when a discrete molecular substance freezes or is vaporized. Indicate the kinds of interactions/bonds that are broken or formed. (3)
• Explain (and illustrate) the energy changes that occur when two atoms approach each other and form a bond. Describe what happens to the energy released upon bond formation and what happens if the bond energy is not "removed". (2-4)
• Explain why only an atom's valence electrons are involved in bonding. (7)
• Explain why oxygen, nitrogen, and carbon form 2, 3, and 4 bonds, respectively (and not more or less). (7)
• Use molecular orbital models of bonding to explain why certain atoms do not form bonds and describe how this influences their macroscopic properties. (7)
• Use appropriate bonding models to explain the properties of metals, diamond, graphite, a pure carbon nanotubes, and other diatomic elemental molecules (like Fl2). (7,8)
• Compare the molecular orbital bond model, the valence bond model, and the hybrid orbital valence bond model, and identify situations where each is uniquely useful (2,5,7,8).