Understandings:
- Lewis (electron dot) structures show all the valence electrons in a covalently bonded species.
- The “octet rule” refers to the tendency of atoms to gain a valence shell with a total of 8 electrons.
- Some atoms, like Be and B, might form stable compounds with incomplete octets of electrons.
- Resonance structures occur when there is more than one possible position for a double bond in a molecule.
- Shapes of species are determined by the repulsion of electron pairs according to VSEPR theory.
- Carbon and silicon form giant covalent/network covalent structures.
Applications and skills:
- Deduction of Lewis (electron dot) structure of molecules and ions showing all valence electrons for up to four electron pairs on each atom.
- The use of VSEPR theory to predict the electron domain geometry and the molecular geometry for species with two, three and four electron domains.
- Prediction of bond angles from molecular geometry and presence of non- bonding pairs of electrons.
- Prediction of molecular polarity from bond polarity and molecular geometry.
- Deduction of resonance structures, examples include but are not limited to C6 H6,CO32- and O3.
- Explanation of the properties of giant covalent compounds in terms of their structures
|
Theory of knowledge:
- Does the need for resonance structures decrease the value or validity of Lewis (electron dot) theory? What criteria do we use in assessing the validity of a scientific theory?
Utilization:
- Syllabus and cross-curricular links:
- Option A.7—biodegradability of plastics
- Biology topic 2.3—3-D structure of molecules and relating structure to function
Aims:
- Aim 7: Computer simulations could be used to model VSEPR structures.
|
Guidance:
- The term “electron domain” should be used in place of “negative charge centre”.
- Electron pairs in a Lewis (electron dot) structure can be shown as dots, crosses, a dash or any combination.
- Allotropes of carbon (diamond, graphite, graphene, C60 buckminsterfullerene) and SiO2 should be covered.
- Coordinate covalent bonds should be covered.
|
|