CHEM1011 Lecture Notes - Lecture 15: Hydrogen Bond, Valence Bond Theory, Valence Electron
CHEM1011 – Chemistry 1A – Part 10
LEC 15: Valence Bond Theory
Theory
• Limitations of Lewis structures and VSEPR:
o Do’t desrie shape of oleular oritals
o Do’t show how eletros are shared etwee ods
• Valence Bond Theory: shows how orbitals behave in a molecular shape. It is an
extension of VSEPR and AO theories.
o Valence electrons on atoms can be considered to hybridise where all
electrons are of equal energy.
• Hybridised orbitals have a hybrid orbital shape of the two standard orbitals it is
composed of.
LEC 15: Intermolecular Forces
Theory
• States of matter depend upon the strength and nature of forces between atoms
and molecules in the substance.
• A substance will remain in its condensed state (solid or liquid) if its molecules
have too little energy to overcome the intermolecular forces of attraction.
• Dipole-dipole forces: when two molecules with permanent dipoles attract each
other to their oppositely charged sides.
• Dispersion forces: molecules without a permanent dipole can become
temporarily polarised when colliding with other molecules that cause its electron
cloud to distort. Occur between all molecules.
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