CHE-2201 Lecture Notes - Lecture 1: Valence Bond Theory, Valence Electron, Atomic Orbital

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School
Department
Course
Professor
Organic Chemistry I
FALL SEMESTER 2016
Dr. Keith Learn
learnks@appstate.edu
Chapter 1
1.1 Organic Chemistry
Organic chemistry: the study of carbon-containing molecules and their reactions
What happens to a molecule during a reaction?
A collision
Electrons reorganize
Bonds break/form
The BIG question: WHY do reactions occur?
FOCUS ON THE ELECTRONS
What Makes Carbon So Special?
Atoms to the left of carbon GIVE UP electrons
Atoms to the right of carbon ACCEPT electrons
Carbon SHARES electrons - generally forms four bonds
1.2 Structural Theory
In the mid 1800s, it was first suggested that substances are defined by a specific arrangement of
atoms (structure determines function); despite having the same molecular formula some
molecules are not the same
Isomer: different substances with the same formula
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Atoms that are most commonly bonded to carbon include N, O, H, and halides (F, Cl, Br, I)
1.3 Covalent Bonding
A covalent bond is a PAIR of electrons shared between two atoms
Bonds won’t form unless attractive forces overcome repulsive forces - point where attractive >
repulsive, then after that repulsive > attractive
1.4 Formal Charge
A formal charge is associated with any atoms that does not exhibit the appropriate number of
valence electrons
To calculate formal charge for an atom, compare the number of valence electrons that SHOULD
be associated with the atom to the number of valence electrons that are ACTUALLY associated
with an atom
More electrons - negative charge
Less electrons - positive charge
1.5 Polar Covalent Bonds
Covalent bonds are electron pairs that exist in an orbital shared between two atoms
Just like an atomic orbital, the electrons could be anywhere within that orbital region
Covalent bonds are either polar or nonpolar
Nonpolar covalent: bonded atoms share electrons equally
Difference between electronegativity < 0.5
Polar covalent: one of the atoms attracts electrons more than the other
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Document Summary

Organic chemistry: the study of carbon-containing molecules and their reactions. Atoms to the left of carbon give up electrons. Atoms to the right of carbon accept electrons. Carbon shares electrons - generally forms four bonds. In the mid 1800s, it was first suggested that substances are defined by a specific arrangement of atoms (structure determines function); despite having the same molecular formula some molecules are not the same. Isomer: different substances with the same formula. Atoms that are most commonly bonded to carbon include n, o, h, and halides (f, cl, br, i) A covalent bond is a pair of electrons shared between two atoms. Bonds won"t form unless attractive forces overcome repulsive forces - point where attractive > repulsive, then after that repulsive > attractive. A formal charge is associated with any atoms that does not exhibit the appropriate number of valence electrons.

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