lewis structures and the “real” 3d-shape of molecules · a. molecular shape or geometry - the...
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Lewis Structures and the “Real” 3D-Shape of Molecules
Sulfanilamide
A. Molecular Shape or Geometry - The way in which atoms of a molecule are arranged in space. It refers to the actual position of the nuclei.
B. What influences molecular shape ? The major factor is the tendency of valence electrons whether they are involved in bonding or not to repel each other.
C. The theory which describes molecular shape is called
VALENCE SHELL ELECTRON PAIR REPULSION
Because of their negative charge valence electrons will arrange themselves about a central atom in a way that minimizes repulsion between electrons.
D. Why is molecular shape important?
1. Molecular shape influences molecular polarity (the degree of separation of plus and minus charges in a molecule)
2. Molecular polarity influences such physical properties as melting point, boiling point, and solubility.
Shapes and Polarities of Molecules
Common molecular shapes include:
1. Linear 2. Bent (angular) 3. Triangular
4. Tetrahedral 5. Pyramidal
H Cl
Hydrogen Chloride, HCl, a Linear Molecule
HOH
Water, H2O, a Bent or Angular Molecule
Ammonia, NH3, a Pyramidal Molecule
HNHH
Methane, CH4, a Tetrahedral Molecule
CH
HH
H
VSEPR Arrangements of Groups Around an Atom
Electron Groups are Single Bonds, Multiple Bonds, or Unshared Pairs of Electrons
H O H O O O
VSPER Molecular Shape Table
HC O
H
Formaldehyde, CH2O, a Planar, Triangular Molecule
H BH
H
Borane, BH3, a Planar, Triangular Molecule
O C O
Carbon Dioxide, CO2, a Linear Molecule
H C C H
H C N
Acetylene and Hydrogen Cyanide, Linear Molecules
Covalent Bonds Exist in a Continuum
When describing the polarity of a molecule, we must consider bond polarities as
VECTOR QUANTITIESquantities with magnitude and direction.
Some molecules are inherently polar because of the atoms which they contain and the arrangement of these atoms in space.
H2O NH3 CH2O HCl
δ− δ+ A crude representation of a polar molecule
Other molecules are considered nonpolar
CH4 BH3 C2H2 CO2
Nonpolarizedelectronclouds
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