Exam

• isotope


  element with a different number of neutrons
• mass spectrometry


  mass of various isotopic elements to create a mass spectrum graph
• avogadros number


  6.022 E23
• ? L/mol


  22.4 L
• empirical formula


  simplest ratio of the molecules making up a compound
• molecular formula


  actual formula for a substance
• coulombs law


  the amount of energy that an electron has depends on its distance from the nucleus of an atom; e=k(q1*q20)/r
• ionization energy


  amount of energy necessary to remove electrons from an atom (electromagnetic energy exceeds binding energy)
• shielding electrons


  electrons between a valence electron and the nucleus that decreases the attraction between the nucleus and the valence electron
• periodic trend: left to right

  periodic trend: atomic radius decreases; protons are added to the nucleus so valence electrons are more strongly attracted

  
  

  ionization energy increases (protons are added to the nucleus)
• periodic trend: down a group


  periodic trend: atomic radius increases; shells of electrons are added which shield the more distant shells and valence e- get farther away

  
  

  ionization energy decreases (shells of e- added, each inner shell shields more and reduces the pull on valence e- so they are easier to remove)
• ionic bond


  bond between metal and nonmetal; electrons are NOT shared: the cation gives an e- up to the anion

  
• metallic bonding


  bond between two metals; sea of electrons that make metals such good conductors; delocalized structure allows for malleability and ductility
• interstitial alloy


  metal atoms with vastly different radii combine; ex. steel

  
• substitutional alloy


  metal atoms with similar radii combine; ex. brass

  
• covalent bonds


  bond in which two atoms share electrons; each atom counts the e- as a part of its valence shell

  
• single bonds


  one sigma bond, one e- pair; longest bond, least energy
• double bonds


  one sigma bond, one pi bond; two e- pairs
• triple bonds


  one sigma bond, two pi bonds; 3 e- pairs; shortest bond, most energy
• network covalent bonds


  lattice of covalent bonds; network solid (acts similar to one molecule); very hard, high melting/boiling points; poor conductors
• the common network solids

  SiO2,
• doping


  the addition of an impurity to an existing lattice
• p-doping


  create a hole (positively charged) that draws electrons through the substance (add a substance with one LESS valence e-) i.e. si + al
• n-doping


  add a substance with one MORE valence e- which leaves a free e- to travel freely

  i.e. si + p
• polarity


  exists when a molecule has a clustering of negative charge on one side due to unequal sharing of electrons (e- are pulled to the more electronegative side); creates dipoles in molecules
• dipole moment


  the measurement of the polarity of a molecule; the unit of measurement is a debye (D)

  
• more polar molecule....


  .... larger dipole moment
• intermolecular forces (IMFs)


  forces that exist between molecules in a covalently bonded substance; not bonds
• dipole-dipole forces


  the positive end of one polar molecule is attracted to the negative end of another molecule; relatively weak attraction force

  
• hydrogen bonding


  strong IMF between two moelcules; F, O, N; have higher melting and boiling points than molecules with other IMFs

  
• london dispersion forces


  IMFs that occur between all molecules; occur because of the random motions of electrons on atoms within molecules to create instantaneous polarities; molecules with more e- will have greater _________________ forces
• substances with only london dispersion forces usually...

  ... are gases at room temp, and boil/melt at extremely low temps
• melting & boiling points of a covalent substance is almost always _____________ than that of ionic substances

  lower
• vapor pressure


  the pressure exerted by a vapor over a liquid
• resonance structures


  structures that occur when it is possible to draw two or more valid lewis electron dot diagrams that have the same number of electron pairs for a molecule or ion
• formal charge


  used to find which structure is most likely to occur; valence - assigned
• linear geometry


  sp hybridization

  0 lone pairs

  ex. BeCl2 & CO2

  
• trigonal planar geometry


  sp2 hybridization

  bond angles 120

  0 lone pairs: trigonal planar (three bonds)

  1 lone pair: bent (two bonds)

  
• tetrahedral geometry


  4 e- pairs, sp3 hybridization

  angles 109.5

  0 lone pairs: tetrahedral (four bonds) [CH4, NH4+, ClO4-, SO4 2-, PO4 3-]

  1 lone pair: trigonal pyramidal (3 bonds) [NH3, PCl3, SO3 2-]

  2 lone pairs: bent (2 bonds) [H2O, OF2, NH2-]

  
• trigonal bipyramidal geometry


  5 e- pairs, sp4 hybridization

  0 lone pairs: trigonal bipyramidal (5 bonds) [PCl5, PF5]

  1 lone pair: seesaw (4 bonds) [SF4, IF4+]

  2 lone pairs: t-shaped (3 bonds) [ClF3, ICl3]

  3 lone pairs: linear (2 bonds) [XeF2, I3-]