chemical bonding

Question 1

electronegativity
(definition and factors affecting it)

Answer 1

• a measure of an atom’s ability to attract the electrons in a covalent bond to itself
• effective nuclear charge
  => explains why electronegativity increases across period
• number of quantum shells
  => explains why electronegativity decreases down grp

Question 2

lattice energy

Answer 2

• defined as heat evolved when
  1 mole of a pure ionic solid is formed
  from its constituent gaseous ions
• proportional to [(q+) x (q-)] / [(r+) + (r-)]
• note: larger magnitude of lattice energy / more exothermic lattice energy
  => stronger ionic bonding

Question 3

ionic bonding
(definition and factors affecting its strength)

Answer 3

• the electrostatic foa between oppositely charged ions
• affected by lattice energy

Question 4

factors affecting strength of covalent bonding

Answer 4

• bond energy: the average amount of energy
  required to break 1 mole of a covalent bond in the gaseous state
  to form gaseous atoms
• bond length (which indirectly depends on size of atoms)
  
  • smaller atoms
    -> more effective overlap between orbitals
    -> shorter and stronger bonds
  • bond order (i.e. no of bonds)
    
    • multiple bonds
      -> more electrons being shared
      -> attraction between 2 positively charged nuclei and shared electrons is stronger
• type of hybridisation
  
  • higher % p character
    -> bond being longer and weaker
    
    • sp3 = 75% p character
    • sp2 = 66.6% p character
    • sp = 50% p character

Question 5

definition of ionic bonding

Answer 5

the electrostatic foa between the metal cations and the sea of delocalised electrons

Question 6

factors affecting strength of ionic bonding

Answer 6

• number of valence electrons contributed per atom
  
  • larger number -> greater number of delocalised electrons
• charge density = (ionic charge) / (ionic radius)

Question 7

definition of dispersion forces

Answer 7

attraction between instantaneous and induced dipoles
- fluctuations in electron distribution causes instantaneous dipole in 1 molecule
- which induces a dipole in another molecule

Question 8

factors affecting strength of df

Answer 8

• number of electrons in the molecule
  (look at Mr / Ar of molecule / atom)
  
  • larger no of electrons / electron cloud
    -> more polarisable
    -> stronger df
• larger SA
  -> more easily induced dipoles formed
  -> stronger df
  
  • usually elongated vs circular shape
    -> elongated has larger SA

Question 9

definition of pd-pd attractions/interactions

Answer 9

attraction between oppositely-charged ends of 2 polar molecules

Question 10

definition of hydrogen bonding

Answer 10

• bonding electrons in H-A bond are pulled strongly towards highly electronegative A atom (N, O, F)
• H atom is now highly electron deficient
• lone pairs on B (N, O, F) attracts the electron deficient H atom strongly
  => H bond

Question 11

factors affecting hydrogen bonding

Answer 11

strength:
- electronegativity of atom H atom is bonded to
- more electronegative atom
-> more electron deficient H atom
-> lone pairs on B atom attracts electron deficient H atom more strongly
=> stronger H bond
- intramolecular H bonding
- occurs when electron deficient H atom is in close proximity to lone pairs on atoms (N, O, F) in the same molecule
- intramolecular H bonding -> weaker H bonding

extent:
- number of H atoms bonded to highly electronegative A atom and number of lone pairs available
- form more hydrogen bonds per molecule => more extensive H bonding
- note: to form x H bonds per molecule,
must have x e-deficient H atoms
AND x lone pairs available

Question 12

all shapes involving 2 bond pairs

Answer 12

2 bond pairs, 0 lone pairs => linear, 180º
2 bond pairs, 1 lone pair => bent, <120º
2 bond pairs, 2 lone pairs => bent, 104.5º
2 bond pairs, 3 lone pairs => linear, 180º

Question 13

all shapes involving 3 bond pairs

Answer 13

3 bond pairs, 0 lone pairs => trigonal planar, 120º
3 bond pairs, 1 lone pair => trigonal pyramidal, 107º
3 bond pairs, 2 lone pairs => T-shaped

Question 14

all shapes involving 4 bond pairs

Answer 14

4 bond pairs, 0 lone pairs => tetrahedral, 109.5º
4 bond pairs, 1 lone pair => see-saw
4 bond pairs, 2 lone pairs => square planar, 90º

Question 15

all shapes involving 5 bond pairs

Answer 15

5 bond pairs, 0 lone pairs => trigonal bipyramidal
5 bond pairs, 1 lone pair => square pyramidal

Question 16

all shapes involving 6 bond pairs

Answer 16

6 bond pairs, 0 lone pairs => octahedral, 90º