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Covalent Bonds and Molecular Shapes
Chapter One of Brown/Foote O Chem Book, Purdue CHM 255
36
Organic Chemistry
Undergraduate 2
12/11/2012

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Cards

Term
Aufbau Principle
Definition
Orbitals fill in order of increasing energy, from lowest to highest.
Term
Pauli Exclusion Principle
Definition
Only two electrons can occupy an orbital. Their spins must be paired(i.e., they must be in the opposite direction).
Term
Hund's Rule
Definition

1. When orbitals of equal energy [degenerate] are available but there are not enough electrons to fill all of them completely, then one electron is added to each orbital before a second electron is added to any of them.

2. The spins of single electrons in the degenerate orbintals must be aligned

Term
electronegativity
Definition
the measure of an atom's attraction for electrons that is shares in a chemical bond with another atom
Increases to top and right of periodic table
Term
electron affinity
Definition
the energy released upon additino of an electron. Increases down and left.
Term
covalent bond
Definition
formed by sharing of one or more pairs of electrons between two atoms to give a noble gas configutration at each atom
Term
polar covalent bond
Definition
a covalent bond with a electronegativity difference of 0.5 to 1.9
Term
non-polar covalent bond
Definition
a covalent bond with an electronegativity difference of less than 0.5
Term
bond dipole moment
Definition
the product of the charge e on one of a molecules atoms times the distance d seperating the two atoms
μ=e*d
Term
Steps for determing lews structures for polyatomic ions
Definition

1. determine number of valence electrons (add valence electrons by each atom +/- ions)

2. Determine connectivity

3. Connect atoms with a single bond

4. If two atoms share only a single pair of electrons: single bond. If two: double. If three: triple.

Term
[image]
Definition
Ammonia, NH3
Term
[image]
Definition
Ethylene (ethene)
Term
[image]
Definition
Acetylene (ethyne)
Term
[image]
Definition
formaldehyde (Methyl aldehyde)
Term
[image]
Definition
Carbonic acid
Term
Formal Charge
Definition
FC=#valence in neutral atom - (unshared + (1/2)*shared)
Term
Alcohols
Definition
-OH (hydroxyl) group bonded to a tetrahedral carbon atom.
Term
Amines (amino group)
Definition

a molecule with a nitrogen bondeed to one, two, or three carbon atoms by single bonds
primary -> C+NH2
secondary-> C+NH1

tertiary -> C+N

Notice this classification system of 1, 2, 3rd order is different than other fxnl groups

 

Term
Aldehydes
Definition

A compound containing -CHO group

[alternatively written -CH=O]

Term
Ketone
Definition
a compound containing a carbonyl group (=O) bonded to two atoms
Term
Carboxylic Acid/Carboxyl Group
Definition
A compound containing a craboxyl (-COOH) group. Also writeen -CO2H
Term
Esters
Definition
carbonyl adjacent to an ether linkage
Term
Ether
Definition
 R–O–R'
Term
Aryl
Definition
any group containing an aromatic ring
Term
Amide
Definition
Also called carboxylic amide, derivative of carboxylic acid in which -OH is replaced by an amine
Term
Linear Geometry
Definition

2 electron groups

2 bonding

180 degress

Term
Trigonal Planar
Definition

3 electron groups

3 bonding

120 Degrees

Term
Tetrahedral
Definition

4 Electron groups

4 bonding

109.5 degrees

Term
Tetrahedral/Trigonal pyramidal
Definition

4 electrong groups

3 bonding

1 lone pair

107 degrees

Term
Tetrahedral Bent
Definition

4 Electrong groups

2 Bonding

2 Lone Pairs

104.5 Degrees

Term
Trigonal Bipyramidal
Definition

5 Electrong Groups

5 Bonding

90/120 degrees

Term
Octahedral
Definition

6 Electron Groups

6 Bonding

90/90 degrees

Term
∏ bonds
Definition

covalent bonds formed when two p orbitals overlap one another. Not as strong as sigma orbitals

 

Term
sigma bonds
Definition

strongest of all chemical covalent bonds

occurs in sp overlaps (single bonds)

Term
Rules for Writing Contributing Structures
Definition

1. Contributing Structures must have the same number of valence electrons

2. all contributing structures must obey the rules of covalent bonding (no more than 2 electrons in the valence shell of 2nd order, etc)

3. Positions of all nuclei must be the same in all contributing structures; contributing structures differ only in distribution of valence electrons

4. All structures have same # of pair/unpaired electrons

Term
Estimating the relative importance of Contributing stuctures
Definition

Preference 1. Filled Valence Shells

Preference 2. Maximum Number of Covalent Bonds

Preference 3. Least separation of Unlike Charges

Preference 4. Negative Charge on a More electronegative atom

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