Genchem2

• Lewis Structure


  Bonding between atoms of a molecule and the lone pairs of electrons that may exist in the molecule
• Lewis Structure Examples

  • Hydrogen Gas
  • Methane
  • Neon
  • Carbon Dioxide
• Intermolecular Forces


  Forces of attraction between molecules
• Types of Intermolecular Forces

  • London Dispersion Forces
  • Dipole-dipole Forces
  • Hydrogen Bonds
  • Ion-Dipole Forces
• Electronegativity


  Measures the ability of the element to attract two electrons when bonded to another atom. The higher the value, the more the atom can attract pair of electrons
• Electronegativity trend: Increasing from left to right of periodic table, Decreasing from top to bottom of periodic table
• London Dispersion Forces


  Named after Fritz Wolfgang London. Weakest type of intermolecular force of attraction and only exist when atoms are in very close range. The only forces existing among atoms in a noble gases and nonpolar molecular compounds
• Dipole-dipole Force


  Interaction between polar molecules. A dipole is two charges separated by a distance. Result of molecules with positive end in one side and negative end on the other side
• The larger the dipole moment, the stronger the dipole-dipole attraction
• Hydrogen Bond


  An attractive force in polar molecules containing hydrogen (H) atom bonded to a strongly electronegative atom such as Fluorine (F), Oxygen (O) and Nitrogen (N). Molecules linked by hydrogen bonds have high boiling points
• Ion-dipole Force


  An attractive force between ionic molecules and polar molecules. The cation attracts the negative end of a neutral polar molecule
• Kinetic Molecular Theory of Liquids

  • The intermolecular attractive forces are strong enough to hold particles together
  • Liquids are more dense and less compressible than gases
  • Liquids have definite volume, independent of the size and shape of their container
  • The attractive forces are not strong enough to keep neighboring molecules in a fixed position and molecules are free to move past or slide over one another or have the capacity to flow
• Kinetic Molecular Theory of Solids

  • The intermolecular forces between neighboring particles are strong enough to keep them locked in position
  • Solids (like liquids) are not very compressible due to the lack of space between particles
  • If the particles in a solid adopt a highly ordered packing arrangement, the structures are said to be crystalline
• Factors affecting the state of a substance

  • Temperature
  • Pressure
• Cooling a gas may change the phase to a liquid. Cooling a liquid may change the phase to a solid
• Increasing the pressure on a gas may change the state to a liquid. Increasing the pressure on a liquid may change the state to a solid
• Postulates of Kinetic Molecular Theory

  • Matter is made of particles that are constantly in motion. This energy in motion is called the kinetic energy
  • The amount of kinetic energy in a substance is directly proportional to its temperature
  • There is a space between particles. The amount of space in between particles is related to the substance's state of matter
  • Phase changes happen when the temperature of the substance changes sufficiently
  • There are attractive forces in between particles called intermolecular forces. The strength of these forces increased as particles get closer together
• Properties of Liquids


  • They are fluid and they can flow. The liquid particles having relatively more energy than solid particles is what allows liquids to flow
  • Liquids have definite volume, but not a definite shape
  • Liquids have low compressibility
  • The types of intermolecular forces in a liquid depend on the chemical make-up of the liquid itself
  • The higher the kinetic energy, the weaker the intermolecular forces of a substance
• Properties of Liquids


  • Surface Tension
  • Viscosity
  • Capillarity
  • Vapor Pressure and Boiling Point
  • Molar Heat of Vaporization
• Surface Tension


  The property of the surface of a liquid that allows it to resist an external force, due to the cohesive nature of the water molecules. The cohesive forces between molecules in a liquid are shared with all neighboring molecules
• Viscosity


  The quantity that describes a fluid resistance to flow. Fluid resist the relative motion of immersed objects through them as well as to the motion of layers with differing velocities within them. Kinematic viscosity is the ratio of the viscosity of a fluid to its density. It is the measure of the resistive flow of a fluid under the influence of gravity
• Viscosity is normally dependent of pressure, but liquids under extreme pressure often experience an increase in viscosity
• Capillarity


  The rise or depression of a liquid in a small passage such as tube of small cross-sectional area, the spaces between the fibers of a towel or the openings in a porous material. Capillarity is not limited to the vertical direction
• Cohesive Properties


  Cohesion is the ability of like molecules to stick together. Water is strongly cohesive (it will form hydrogen bonds)
• Adhesive Properties


  Adhesion is the ability of dissimilar molecules to stick together. Water will form intermolecular associations with polar and charged molecules
• Vapor Pressure


  The pressure exerted by a vapor in thermodynamic equilibrium with its condensed phases (solid or liquid) at a given temperature. The equilibrium vapor pressure is an indication of a liquid's evaporation rate
• As the temperature of a liquid increases, the kinetic energy of its molecules also increases, thus the energy of the molecules also increases. The number of molecules transformed into a vapor pressure increases, thereby increasing the vapor pressure
• Normal Boiling Point


  The temperature at which the vapor pressure equals the surrounding atmospheric pressure
• Molar Heat of Vaporization


  The energy required to transform a given quantity (a mol, kg, pound, etc.) of a substance from a liquid into a gas at a given pressure (often atmospheric pressure). Liquids may change to a vapor at temperatures below their boiling points through the process of evaporation. Boiling point is a process in which molecules anywhere in the liquid escape, resulting in the formation of vapor bubbles within the liquid
• Kinetic Molecular Theory of Solids

  • Solids substances have definite shapes and volumes
  • Solid particles do move, but not very far
  • Solid particles have relatively kinetic energy and vibrate in place
  • Most solids are arranged in a tightly packed crystalline structure
• Properties of Solids


  • Electrical and Thermal Conductivity
  • Malleability and Ductility
  • Melting Point
  • Solubility
  • Density
• Electrical and Thermal Conductivity


  • Electricity is a flow of electrons from one place to another
  • Materials that do not conduct electricity are called electrical insulators
  • Solids that have low heat conductivity are known as heat insulators
• Malleability and Ductility


  • Malleability describes the ability to hammer a solid into a sheet without breaking it
  • Ductility refers to whether a solid can be stretched to form a wire
  • Metallic malleability and ductility are a crucial reason that metals are so useful
• Melting Point


  A solid's melting point depends on the strength of the interactions between its components: the stronger the attraction, a higher melting point
• Solubility


  • The extent to which a solid dissolves in particular solvent
  • Dissolving a solid requires breaking different types of bonds for different types of solids
• Density


  • The amount of mass per unit volume that depends on the solid's structure and composition
  • Metallic solids do not all share a similar arrangement of atoms
• Some Essential Properties of Solids

  • A solid has definite volume and definite shape
  • A solid is rigid and cannot be compressed easily
  • A solid does not diffuse into another solid easily
  • A solid does not flow and can be stored in a container
  • A solid on heating usually changes into its liquid state
• Crystalline Solids


  • In crystalline solids, the atoms, ions, or molecules are arranged in an ordered and symmetrical pattern that is repeated over the entire crystal
  • The smallest repeating structure is called a unit cell
• Crystalline Solids


  • Generally incompressible
  • Have a distinct melting point
  • Exhibit anisotropy (refractive index, conductivity and tensile strength)
• Types of Crystalline Solids

  • Ionic Solids
  • Molecular Solids
  • Network Covalent Solids
  • Metallic Solids