IB Chemistry Topic 4.3 Covalent structures

IB Chemistry Topic 4.3 Covalent structures
The EASIEST AND BEST WAY to draw any Lewis structure. How VSEPR theory determines the shape of the molecule. How to use Lewis structures to determine if resonance occurs. A look at some specific examples of covalent lattice structures and allotropes.

0:14 Lewis structures
5:13 VSEPR theory
8:26 Resonance structures
11:13 Covalent lattice structures and allotropes

4.3 Covalent structures SL
• 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.
• 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 C6H6, CO32- and O3 .
• Explanation of the properties of giant covalent compounds in terms of their structures.

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