Chem HL topic 4/14

• if the electron negativity difference is greater than 1.7 it is

  Ionic
• Ionic compounds are packed together in a ---(1) making them --(2)

  1 - crystal lattice 2- solid
• Ammonium is ---(1) and ammonia is --- (2)

  (1) NH4 (2) NH3
• what are exceptions to the octet rule?

  beryllium (4 electrons), boron (6 electrons) and period 3 non-metal ie. sulfur and phosphorous (more than 8 electrons).
• Pure covalent bonds

  When electrons are shared equally between 2 or more of the same non-metal (equal/same electronegativity) - HOBrFINCL
• polar covalent bonds

  electrons are shared unequally since one atom has higher electronegativity. The atom with higher electronegativity pulls the electron closer, thus is more negative than the other.
• Coordinate covalent/dative bonds

  when both electrons shared in a covalent bond come from the same atom
• examples of coordinate covalent

  Carbon monoxide and ammonium
• What are free radicals

  a molecule with an odd amount of electrons or a broken bond causing them to be super unstable, thus highly reactive as it tries to get electrons and stabilize.
• What are the polyatomic ions?

  NO3 (nitrate) OH- (hydroxide) NH4+ (ammonium) SO4 2- (sulfate) SO3 2- (sulphite) CO3 2- ( carbonate) HCO3 -1 ( hydrogen carbonate) PO4 3- (phosphate)
• Ozone AND oxygen: Oxygen

  Oxygen is stable and diatomic. Oxygen's bond is a relatively stable double bond + Oxygen's bond length is shorter than ozone and higher energy required to break bonds
• Ozone AND oxygen: Ozone

  unstable. its bonds are two resonance structure with 1 double bond and 1 single bond and lower energy required to break bonds. ozone mechanisms (MEMORIZE)
• Bond lengths info

  Longer bonds mean weaker nuclear pull, thus easier to break
• shorter bonds

  Shorter bonds mean stronger nuclear pull, thus harder to break.
• Shorter bonds are stronger and longer bonds are weaker.
• Larger noble gases are able to bond because 

   shielding reduces nuclear pull so electrons are more easily shared with other atoms.
• What does VSPER /Valence Shell Electron Pair/Domain Repulsion Theory state?

  BP and LP around an atom in a molecule are positioned to minimize mutual interaction because they repel each other.
• What is Resonance Structures?

  when bonding electrons are shared between more than one bonding site (delocalized) to stabilize the molecule.
• Formal Charge

  FC = (number of valence electrons) - (# of non-bonding valence electrons) - (# of electrons bonded to other atoms DIVIDED BY 2)
• What influences polarity?

  Shapes of molecules influences overall polarity.
• Symmetry means 

   charges cancel out so the molecule non-polar.
• BENT IS ALWAYS

  Polar
• Linear is always

  polar or non-polar (depending on diff attached atoms).
• Pyramidal is always

  Polar
• Trigonal Planar is 

  polar or non-polar (depending on diff attached atoms)
• tetrahedral is 

  polar or non polar. (always polar if attached atoms are diff)
• Why do polar molecules have a higher melting point?

   they have dipole-dipole force (plus London Dispersion and sometimes hydrogen bonding ie. H2​O) meaning stronger intermolecular forces which require more energy to overcome.
• what is a covalent bond strength determined by?

   the balance of overlapping atomic orbitals, by nuclear attraction to shared electrons, and repulsion between nuclei.
• Increased atomic overlap means there is better sharing of electrons but

  the closer the nuclei, the more repulsion between atoms.
• Diamond is formed by

  sp3 hybridization; each carbon is attached to 4 others (tetrahedral arrangement)
• then two atoms in a covalent bond have different electronegativities the covalent bond is


  polar and the electrons will be drawn towards the more electronegative atom
• When two atoms in a covalent bond have the same electronegativity 


  the covalent bond is nonpolar
• • The greater the difference in electronegativity the more --- the bond becomes

  polar
• What is the dipole moment


  a measure of how polar a bond is
• The “octet rule”


  refers to the tendency of atoms to gain a valence shell with a total of 8 electrons
• Example of resonance structures 


  Carbonate(CO3(-2)), Benzene (C6H6), Ozone O3, etc
• Two electron domains 


  0 lone pairs therefore only linear (bond angle 180 degrees)
• 3 electron domains


  0 lone pairs = trigonal planar & 1 lone pair = Bent (bond angle is 120 & <120 degrees)
• 4 electron domains


  0 lone pairs = tetrahedral & 1 lone pairs = trigonal pyramidal & 2 lone pairs = Bent (109.5 or <109.5)
• 5 electron domains

  0 lone pairs = trigonal bipyramidal (120 and 90 degrees) &1 lone pair = see-saw (<120 and <90) & 2 lone pairs = T-Shape (90 degree) & 3 lone pairs =linear (90 degrees)