chem bonding

• strength of ionic bond (lattice energy): (q+ x q-)/(r+ + r-)
• factors affecting strength of metallic bond:

  1. no. valence e-: increase, mb increase
  2. charge: increase, mb increase
  3. size of cation (for the same charge): decrease, charge density increase, eFOA between sea of delocalised e- and positive metallic cation, mb increase
• dative bond: shared pair of e- provided from only one of the bonding atoms
• only period 3 and above can have more than 8 electrons: vacant low-lying 3d orbitals to expand its octet structure to form more than one covalent bond
• instantaneous dipole induced dipole interaction: electrons are constantly moving at any given moment, electron density of X molecule can be unsym, resulting in an instantaneous dipole, which induces a short lived dipole in neighbouring X mol, hence idid arises
• factors affecting idid:

  1. no. e- increase: size & ease of polarizability of e- cloud, idid increase
  2. SA increase, idid increase (more branched, SA decrease, idid decrease lower bp)
• H bonds:

  1. polarity of H bonds (F > O > N)
  2. extensiveness of H bonds (avg no. of H bonds per mol, limiting no. of lp & no. of H)
• why ice denser than water?

  each o atom is tetrahedrally bonded to 4 H atoms, 2 by cov bond, 2 by H bonds, enabling H2O mols in ice to form an open 3D network, leading to same no. of H2O mols in ice occupying a larger unit volume
• dimerisation of CA in vapour (or n-p solvents)

  • molar mass of CA in vapour is 2x its calculated molar mass
  • dimer made of 2 CA bonded to eo by H bonds, forming an 8-member ring
  • in aq, CA forms H bonds w H2O instead
• 2-nitrophenol vs 4-nitrophenol

  2 has lower bp and sol

  bp:

  • due to formation of INTRAmolecular H bonds in 2, less sites avail for H bonds with other 2 mols, less extensive INTERmolecular H bonds.
  • lower bp as bp involves overcoming INTERmolecular interactions instead of intra

  sol:

  • when added to H2O, 2 forms less H bonds with H2O due to INTRAmolecular H bonds
• triple bond: 2 pi bond + 1 sigma bond
• labelling: head on head overlap of 3p and 2p orbital of Cl and F respectively
• sigma bond stronger than pi bond as head on head orbital overlap has greater degree of overlap than side on side orbital overlap
• factors of ionic bonds with covalent character:

  1. higher charge density, stronger polarizing power of cation
  2. e- cloud of large anion easier to distort than small anion
• as s-character of hybrid orbital increases, more tightly the shared e- is held by nuclei, greater degree of orbital overlap
• resonance: when there is continuous side on side overlap of p orbitals over at least 3 adjacent atoms, allowing delocalisation of pi electron
• resonance

  same placement of: atoms & sigma bonds

  diff placement of: pi bonds, non-bonding electrons
• resonance explanation


  theory: mol would be unsym, X bond longer than Y bond

  experimental obs:

  • eg. O-O and O=O same bond length, bond length is an intermediate btwn bond length of O-O and O=O
  • reso struct is not an accurate rep, actual structure is a hybrid of them. in reso hybrid, pi electrons delo over ___ via continuous side on side orbital overlap of p-orbitals which are perpendicular to plane of molecule
• benzene: 3 single bonds, 3 double bonds
• resonance hybrid is more stable: delo of e- over a larger volume
• benzene: 6 unhyb p orb overlap side on side, forming a plane of delo pi e- cloud above and below benzene ring
• diamond

  extremely strong and rigid: arise from tetrahedral arrangement repeated throughout the whole molecule with interlocking hexagonal units
• why diamond mp higher than SiO2?

  • valence orbital of Si larger and more diffused than C, less effective orbital overlap, Si-Si bond weaker than C-C bond
• graphite

  layer structure made up of interconnected hexagonal rings of C atoms.
• graphite

  each C has 1 unhyb p orbital which overlaps continuously with p orbital of immediate neighbouring C atom, forming extended pi e- cloud above and below plane containing C atoms
• graphite is an electricity conductor

  pi e- delocalise over whole layer ( can only conduct e- in direction parallel to layers)
• graphite is soft

  idid allows layers to glide over eo