Chemistry Final exam

• Valence Bond Theory


  • A covalent bond forms when the orbitals on two atoms overlap
  • The shared region of space between the orbitals is called the orbital overlap
  • As two nuclei approach each other their atomic orbitals overlap
  • A covalent bond results when (1) an orbital on one atom overlaps an orbital on a second atom and (2) the single electrons in each orbital combine to form an electron pair
• Hybridization


  • The mixing of different types of atomic orbitals to produce a set of equivalent hybrid orbitals
  • Hybrid orbitals do not exist in isolated atoms, they are formed only in covalently bonded atoms
  • Hybrid orbitals have shapes and orientations that are very different from those of the atomic orbitals in isolated atoms
  • The number of hybrid orbitals in a set is equal to the number of atomic orbitals that were combined to produce the set
  • All orbitals in a set of hybrid orbitals are equivalent in shape and energy
  • The type of hybrid orbitals formed in a bonded atom depends on its electron-pair geometry as predicted by the VSEPR theory
  • Hybrid orbitals overlap to form σ bonds, unhybridized orbitals overlap to form π bonds
• sp Hybrid Orbitals


  • The mixing of one s orbital and one p orbital forms two equivalent sp hybrid orbitals
  • According to the valence-bond model, a linear arrangement of electron domains implies sp hybridization
• sp2 and sp3 Hybrid Orbitals


  • Three sp2 hybrid orbitals are formed from hybridization of one s and two p orbitals, with one unhybridized p orbital remaining
  • Four sp3 hybrid orbitals are formed from hybridization of one s and three p orbitals, with each of the four large lobes pointing towards the vertex of a tetrahedron
• sp3d and sp3d2 Hybrid Orbitals


  • Five sp3d hybrid orbitals are formed from hybridization of one s, three p orbitals and 1 d orbital, arranging in a trigonal bipyramidal shape
  • Six sp3d2 hybrid orbitals are formed from hybridization of one s, three p orbitals and 2 d orbitals, arranging in an octahedral shape
• To Assign Hybridization


  1. Draw a Lewis structure

  2. Assign the electron-domain geometry using VSEPR theory

  3. Specify the hybridization required to accommodate the electron domains based on their geometric arrangement

  4. Name the geometry by the positions of the atoms
• σ and π bonding

  • Every pair of bonded atoms shares one or more pairs of electrons
  • Two electrons shared between atoms on the same axis as the nuclei are σ bonds, σ bonds are always localized in the region between two bonded atoms
  • If two atoms share more than one pair of electrons, the additional pairs form π-bonds
  • When resonance structures are possible, delocalization is also possible
• Molecular Orbital Theory


  • Molecular orbitals are associated with an entire molecule, each contains a maximum of two electrons with opposite spins, each has a definite energy, electron density distribution can be visualized with contour diagrams
  • When two atomic orbitals (AO) overlap, two molecular orbitals (MO) form - a bonding MO and an antibonding MO
  • Sigma (σ) MOs have electron density in both molecular orbitals centered about the internuclear axis, the σ bonding MO is lower in energy than the σ* antibonding MO
  • Bond order = ½ (bonding electrons - antibonding electrons), BO = 1 for single bond, 2 for double bond, 3 for triple bond
  • The number of MOs = number of AOs, AOs of similar energy combine, as overlap increases, the energy of the bonding MO decreases and the energy of the antibonding MO increases
  • Pauli: each MO has at most two electrons, with opposite spins, Hund: for degenerate orbitals, each MO is first occupied singly before spin pairing occurs
  • Two ways p orbitals can overlap: end on (σ MO) or sideways (π MO)
• Dissolution Process


  1. Intermolecular forces between solute and solvent particles

  2. Solute-solute interactions

  3. Solvent-solvent interactions

  4. Solvent-solute interactions

  5. Enthalpy change in solution process
• gas constant R


  0.08206 L•atm/mol•K
• Gas Pressure (9.1)


  Pressure is the force acting on an object per unit area: P = F/A

  
• The formation of a solution is an example of a spontaneous process
• Criteria that favor the spontaneous formation of a solution: decrease in internal energy, increased dispersal of matter
• Units of pressure


  • pascal (Pa)
  • bar
  • atmospheres (atm)
  • millimeter of mercury (mm Hg) or torr
• Dissolution and crystallization


  1. Solute + solvent → solution

  2. Solution → solute + solvent
• Atmospheric pressure at sea level is about 100 kPa, or 1 bar, or 14.7 psi
• Saturated solution


  Solution with a concentration of dissolved solute that is equal to the solubility
• Standard atmospheric pressure is the pressure required to support 760 mm of Hg in a column

  
• Bronsted-Lowry acid


  Species that donates H+
• Manometer


  A device used to measure the pressure of a gas trapped in a container
• Unsaturated solution


  Solution with a concentration of dissolved solute that is less than the solubility
• Intermolecular forces


  The forces holding solids and liquids together
• Bronsted-Lowry base


  Species that accepts H+
• The first law of thermodynamics: energy is conserved
• Supersaturated solution


  Solution with more solute dissolved than in a saturated solution
• Conjugate acid-base pair


  Acid and its conjugate base, or base and its conjugate acid
• Relating Pressure, Volume, Amount, and Temperature: The Ideal Gas Law (9.2)


  Four variables are needed to define the physical condition or state of a gas: T (temperature), P (pressure), V (volume), and n (number of moles of gas)
• Intermolecular forces are much weaker than ionic or covalent bonds
• ΔE


  Change in internal energy
• Electrolyte


  Substance that undergoes a physical or chemical change to yield ions in solution
• Strong acids completely transfer their protons to water
• Amonton's or Gay-Lussac's Law


  The pressure of a given amount of gas is directly proportional to its temperature on the kelvin scale when the volume is held constant

  
• Strong electrolyte


  Substance where the ion-producing process is essentially 100% efficient
• q


  Heat absorbed by the system from the surroundings
• Charles's law


  The volume of a fixed quantity of gas at constant pressure is directly proportional to its absolute temperature

  
• Weak acids only partially dissociate in aqueous solution
• w


  Work done
• Boyle's law


  The volume of a fixed quantity of gas, at constant temperature, is inversely proportional to its pressure

  
• Weak electrolyte


  Substance where only a relatively small fraction of the dissolved substance undergoes the ion-producing process
• Melting points and boiling points


  Reflect the strength of attractive forces