vsepr 2

• VSEPR Theory


  Analyze a structure's electron domains to predict the shape around the central atom
• Impact of lone pairs on bond angles

  Each additional lone pair of electrons decreases the bond angles due to increased repulsion with bonding electrons
• Lewis structures

  Show how valence electrons are organized around the atoms within a molecule, around the central atom
• Electron domains in a molecule

  • Double bond, lone pair of electrons, single bond
• Covalent bonds

  Form when non-metals share electrons to achieve a stable electron configuration, compounds formed are called molecules
• Molecules with four electron domains


  • Methane, Ammonia, Water
• Tetrahedral shape

  Representing the shape created by all four electron domains in three-dimensional space
• Electron geometry

  Describes the shape of all electron domains in three-dimensional space
• Bent shape

  Molecular geometry when two electron domains are lone pairs of electrons
• Chemical behavior of molecules

  Determined by their shape and polarity
• Electron domains arrangement

  Constantly repelling each other, pushing to arrange themselves in three-dimensional space to minimize repulsion and maximize bond angles
• Trigonal pyramidal shape

  Shape of the atoms in the molecule when one electron domain is replaced with a lone pair of electrons
• Molecular geometry

  Describes the shape formed by just the atoms in the molecule
• Molecular geometry plays a large role in a molecule's overall polarity and its interactions with other compounds
• Each additional lone pair of electrons occupies more space than electrons stored in bonds

  Increased repulsion with bonding electrons pushes bonds inward, decreasing bond angles
• The presence and orientation of polar bonds, determined by the molecule's geometry, can cause bond dipoles to either cancel out or add together
• Carbon dioxide (CO2) has a linear molecular geometry with a bond angle of 180° due to two electron domains around its central carbon atom
• Replacing one chlorine atom in carbon tetrachloride with a hydrogen atom creates chloroform (Trichloromethane), a polar molecule
• Molecular geometries with three electron domains

  1. Methanal: Central carbon with three electron domains, creating bond angles of 120° in a flat triangle shape, trigonal planar electron and molecular geometries

  2. Ozone: Three electron domains resulting in a trigonal planar electron geometry, with a slightly bent molecular geometry and a bond angle of about 117°
• Water has the smallest bond angle due to the most non-bonded pairs of electrons, while methane has the largest bond angles
• Polar bonds create partial positive and negative charges called bond dipoles
• Bond angles in structures

  • Methane
  • Ammonia
  • Water
• Molecular geometries chart

  • Three electron domains: Trigonal planar
  • Four electron domains: Tetrahedral
  • Two electron domains: Linear
• Carbon tetrachloride and carbon dioxide, despite having polar bonds, are considered non-polar molecules due to the cancellation of bond dipoles
• In a covalent compound, bonds are classified as polar or non-polar based on their differences in electronegativity
• Diamond

  • Tetrahedral geometry, hardest substance known, high melting point
• Learning about the geometry and polarity of carbon compounds is vital to understanding their chemical behavior and intermolecular forces
• Carbon-chlorine bond in Tri chloromethane

  Considered to be polar due to the lack of a fourth dipole moment
• Ammonia

  Polar hydrogen-nitrogen bonds, lone pair of electrons on central nitrogen atom gives it a trigonal pyramidal molecular geometry
• Methanol

  Carbon-hydrogen bonds are non-polar, carbon-oxygen bond is polar
• Carbon-hydrogen bond

  Generally considered to be non-polar due to the small difference in electronegativity between carbon and hydrogen
• Creating Tri chloromethane

  Replacing one chlorine atom in carbon tetrachloride with a hydrogen atom
• Fullerene

  • Trigonal geometry, forms a sphere of 60 carbon atoms, semiconductors, light and strong with a low melting point
• Tri chloromethane

  Considered to be a polar molecule
• Repulsion between bonded and non-bonded valence electrons in carbon structures


  Causes molecules to take shapes known as their electron and molecular geometry
• Graphite

  • Trigonal planar geometry, good conductor of electricity, used in pencils and as a lubricant
• Carbon allotropes

  Graphite, Diamond, Fullerene