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Understanding Lewis Dot Structures
Sep 17, 2024
Lecture on Lewis Dot Structures
Introduction
Focus on drawing Lewis dot structures.
Ions form ionic compounds; covalent bonds form networks.
Representing Atoms
Use chemical symbols for atoms.
Valence electrons are represented as dots around the atom.
Carbon Example
Electron configuration: 1s², 2s², 2p² -> 4 valence electrons.
There are four coordination sites for atoms like carbon.
Fill each coordination site with one electron before pairing.
Similarity Across Groups
Elements in the same group have similar Lewis dot symbols due to similar valence electrons.
Drawing Lewis Dot Structures for Molecules
Draw each atom with its valence electrons.
Unpaired electrons from different atoms form covalent bonds (lines).
Electrons must be paired either in bonds or as lone pairs.
Bond Formation Tendencies
Carbon
: 4 bonds.
Nitrogen
: 3 bonds, 1 lone pair (5 valence electrons).
Oxygen
: 2 bonds, 2 lone pairs.
Fluorine
: 1 bond, 3 lone pairs.
Types of Bonds
Sigma Bond
: Single covalent bond.
Double/Triple Bonds
: Involve pi bonds.
Carbon Dioxide Example
: Unpaired electrons form additional bonds.
Pi Bond
: Second bond in a double bond and second/third in a triple bond.
Bond Lengths
Single bonds are the longest.
Double bonds are shorter.
Triple bonds are the shortest.
Formal Charge
Occurs when electron contribution differs from typical valence.
Ammonia (NH₃)
: Neutral nitrogen atom.
Ammonium Ion (NH₄⁺)
: Nitrogen with formal positive charge (contributes one less electron).
Octet Rule
Atoms seek 8 electrons (n=2 shell filled).
Hydrogen
: Needs 2 electrons (n=1 shell).
Larger Atoms (Phosphorus, Sulfur)
: Can form 5 or 6 bonds.
Conclusion
Combine unpaired valence electrons to form bonds.
For further questions, contact the lecturer.
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