PhySci

• Polar molecule


  Formed when electrons are shared unequally by two atoms in a compound, forming an electric dipole
• Nonpolar molecule


  Formed when both atoms equally share a pair of electrons between them
• Polarity of molecules


  • Depends on electronegativity difference
  • Depends on geometrical shapes of molecules
• Electronegativity (EN)


  Measures the relative tendency of an atom to attract electrons to itself when chemically combined with other atoms
• Electronegativity increases within a group (from left to right)
• Electronegativity increases within a period (from bottom to top)
• Ionic bond


  When a metal and nonmetal atoms bond, the metal ion loses a valence electron and the nonmetal ion accepts the lost electron
• Covalent bond


  Nonmetal ions share valence electrons when they combine
• Polar covalent bond


  Bonding electrons shared unequally between two atoms, resulting in partial charges on atoms
• Nonpolar covalent bond


  Bonding electrons shared equally between two atoms, resulting in no charges on atoms
• Electronegativity difference and type of bonds

  • Ionic bond: ≥ 1.7
  • Polar covalent: 0.5 - 1.6
  • Nonpolar covalent: ≤ 0.4
• Predict the type of bond present between the following pair of atoms by determining their electronegativity difference

  • Ca and Cl
  • Cl and Cl
  • H and Cl
• Collision theory


  Reacting substances must come into contact (collide) with enough activation energy, and in the correct orientation (facing the correct way), so that their electron shells can rearrange to form the products of the reaction
• How to predict molecular geometry through VSEPR

  1. Determine the central atom

  2. Draw the appropriate Lewis Dot Structure

  3. Count the number of bonding pairs of electrons and non-bonding (lone pairs) around the central atom

  4. Determine the electron pair orientation using total number of electron pair
• Chemical reaction


  1. Particles must come into contact with one another or collide

  2. Particles must be aligned correctly so that the right parts of the atoms or molecules are exposed

  3. Particles must collide with enough energy to break their chemical bonds
• Solubility


  The ability of a solid substance to be dissolved in a given amount of solvent
• Reaction rate


  Measurement of the increase in the concentration of a product or the decrease in the concentration of a reactant as the reaction proceeds over time
• Miscibility


  The ability of two liquids to combine or mix in all proportions, creating a homogenous mixture
• Not all reactions occur at the same speed
• The general rule about the solubility and miscibility of molecular compounds is "like dissolves like" or "like mixes with like"
• Rate of reaction depends on the type of molecules that are combining
• General properties of polar and nonpolar molecules

  • Polar molecules: IMFA type: H-bonding and dipole-dipole, exist as solids or liquids at room temperature, high boiling point, high melting point, high surface tension, low vapor pressure, low volatility, soluble in water
  • Nonpolar molecules: IMFA type: London dispersion, exist as gases at room temperature, low boiling point, low melting point, low surface tension, high vapor pressure, high volatility, insoluble in water
• Activation energy


  Minimum energy required for a reaction to take place
• Boiling point


  The temperature at which the vapor pressure and atmospheric pressure of a liquid substance are equal
• Collision provides energy equal to or greater than the activation energy


  Product can form
• Collision provides energy less than the activation energy


  Particles just bounce off each other unchanged
• Melting point


  The temperature at which solid becomes liquid. At this point, the solid and liquid phases exist in equilibrium
• Temperature


  How hot or cold a certain substance is
• Surface tension


  The energy needed to increase the surface area by a unit amount
• Rise in temperature of 10°C

  Doubles the reaction rate
• Viscosity


  The resistance of the liquid to flow
• As temperature increases


  Collision between atoms and molecules becomes faster, resulting in build-up of more energy
• Vapor pressure


  The pressure exerted by a substance in its gaseous state
• Increased kinetic energy equals to or exceeds the activation energy


  More collisions giving rise to a reaction
• Volatility


  The measure of the rate at which a substance vaporizes (changes from liquid to gas)
• Concentration


  Number of particles present in each volume of solution
• Higher concentration of reactant

  Increases the rate of reaction
• More particles of the reactant


  Greater chance for particles to collide
• Surface area


  Measure of how much exposed area a solid object has, expressed in square units
• More finely divided a solid is

  Faster the rate of reaction