PHYSICAL SCIENCE

• Molecule


  A neutral group of two or more atoms held together by chemical bonds
• Important Terms


  • Lone Pair
  • Electronegativity
  • Polar Bond
  • Non-Polar Bond
  • Molecular Geometry
• Polarity


  The distribution of electric charge around atoms, chemical groups, or molecules
• Polar molecule


  Unequal or asymmetrical distribution of electrons among the atoms of a molecule
• Nonpolar molecule


  Equal or symmetrical distribution of electrons among the atoms in a molecule
• Factors that determine polarity of molecules


  • Polarity of the bonds between atoms based on electronegativity
  • Geometrical shape of the molecule predicted via VSEPR theory
• All compounds can be classified as "covalent" or "ionic"
• The polarity of molecules does not depend solely on the type of bond present but also on the shape of the molecules
• Molecular Geometry


  The three-dimensional arrangement of atoms in a molecule
• Molecular Geometry


  • Affects the physical and chemical properties of molecules and their reactivity towards other molecules
  • Can be determined by experiment such as x-ray diffraction
  • Predicted using the Valence Shell Electron Pair Repulsion Theory (VSEPR)
• Lewis Electron Dot Structure (LEDS)


  Used to describe and visualize molecules, showing bonds between atoms and electrons surrounding atoms
• Valence Shell Electron Pair Repulsion (VSEPR) Theory


  Used to predict molecular geometry
• Lewis Structures


  Used to describe and visualize molecules, showing bonds between atoms and electrons surrounding atoms
• Valence Electrons


  The "outermost electrons" of an atom involved in chemical bonding
• Octet Rule


  Atoms tend to form compounds in ways that give them eight valence electrons and thus the electron configuration of a noble gas
• Gilbert Newton Lewis proposed the idea of covalent bonding and the importance of electron pairs in bonding
• Lewis Symbol


  An element's chemical symbol surrounded by dots representing its valence electrons
• VSEPR Theory


  • Electron pairs stay as far apart from each other as possible to minimize repulsions
  • Molecular shape is determined by the number of bond pairs and lone pairs around the atom
  • Treat multiple bonds as if they were single bonds
  • Lone pairs occupy more volume than bond pairs
• Nonpolar Molecule


  The shape of the molecule is symmetrical, with equal sharing of electrons and no dipole moment
• Polar Molecule


  The shape of the molecule is asymmetrical, with unequal sharing of electrons and a dipole moment
• Miscibility


  The ability of a liquid solute to dissolve in a liquid solvent
• Solubility


  The ability of a solid solute to dissolve in a liquid solvent
• Intramolecular Forces


  Forces within molecules or the forces holding a molecule together
• Intermolecular Forces


  Attractive forces present between molecules
• Types of Intermolecular Forces


  • London Dispersion Forces
  • Dipole-Dipole Forces
  • Hydrogen Bonding
• London Dispersion Forces


  Formed due to the attraction between the positively charged nucleus of an atom with the negatively charged electron cloud of a nearby atom
• Dipole-Dipole Forces


  Occur between polar molecules due to the partial positive and negative poles
• Ion-Dipole Force


  Result from the electrostatic attraction of a molecule containing a dipole and an ion
• Hydrogen Bond


  A very strong dipole-dipole interaction that occurs in polar molecules containing H and highly electronegative elements like F, O, N
• Stronger intermolecular forces


  Molecules are packed closer together, often existing as condensed phase (solid or liquid) at room temperature
• Weaker intermolecular forces


  Molecules are farther apart, often existing as gas at room temperature
• Stronger intermolecular forces


  Substances have higher melting and boiling points, higher surface tension, and higher viscosity
• Stronger intermolecular forces


  Substances have lower vapor pressure
• Strategies for comparing intermolecular force strengths


  • Check for hydrogen bonding, polarity, and molecular weight
• Intermolecular forces


  Attractive forces that act between molecules or atoms of pure substances. Also called van der Waals forces
• Types of intermolecular forces


  • Ion-ion interaction
  • Dipole-dipole interaction
  • Ion-dipole interaction
  • Hydrogen bonding
  • London dispersion force
• Ion-ion interaction


  Forces that act between ion molecules
• Dipole-dipole interaction


  Forces that act between polar molecules
• Ion-dipole interaction


  Forces that act between ion and polar molecules
• Hydrogen bonding


  A special kind of dipole-dipole force and one of the strongest type of intermolecular forces