3: intermol forces / valence bond theory / molec orbital theory

Question 1

when weak temporary dipoles are caused by changes in e- density

Answer 1

dispersion forces

Question 2

how to H bond

Answer 2

when H bonded to a <EN atom ( N O F) and lone pairs on another molec

strongest

Question 3

boiling point vs melting point: definition and increasing factor

Answer 3

temp at which vapour P = atmospheric P and break intermol forces vs (s) and (l) forces at equi

<SA vs <symmetry

Question 4

if a molecule can H bond or ionic bond, its boiling and melting point can increase T OR F

Answer 4

T

Question 5

state valence bond theory

Answer 5

1. cov bonds are formed by orbital overlap
2. these e- are localized in 1 area
3. orbitals hybridize before bond formation

Question 6

how to create hybrid orbitals?

Answer 6

atomic orbitals mix to form hybrid orbitals

s p p p => 4 sp3 hybrid orbitals (apply VSPER theory)

Question 7

what is cis/trans isomerism?

Answer 7

from TT bonds unable to rotate

= formual, = atom connectivity bt diff spatial arrangement

Question 8

how to create sp2 hybridization?

Answer 8

combine the wavefunction of one 2s orbital and two 2p orbitals to form sp2 hybrid orbitals
trigonal planar
leftover p orbitals for TT orbitals

Question 9

how to create sp hybridization

Answer 9

combine the wavefunciton of one 2s orbital and one 2p orbital to form two sp hybrid orbitals
leftover p orbital to form TT orbitals
linear

Question 10

wha’s in a double bond

Answer 10

1 sigma + 1 TT bond
sigma bond are formed from direct overlap of hybrid orbitals
TT bonds are formed by sideway overlap or leftover p orbitals => unable to rotate

Question 11

why was Molecular Orbital theory develop?

Answer 11

from the failures of VB theory
1. VB theory takes a localized approad to bonding and fails to explore reasonance which has delocalized e-)

2. offer no info on relative enrg of e- in molec
3. fail to predict paramagnetic / diamagnetic

Question 12

so what is MO theory?

Answer 12

electrons are delocalized
bonding based on wave behaviour of e-
at anu given moment, wave in 1 phase (above or below)

Question 13

how to find bond order for MO theory

Answer 13

= (# of bonding e- —- # of antibonding e-)/2

Question 14

paramagnetic vs diamagnetic

Answer 14

para: attacted to magnet, have atg least 1 unpaired e-
dia: not attracted to magnet, filled

Question 15

principles of MO theory

hint: obey 3 rules and related to atomic orbitals

Answer 15

1. # of MO = # of AO
2. MO is lower in energy than atomic orbitals, antibonding orbitals are higher
3. must obey Aufbau Principle / Pauli Exclusion Principle / Hund’s Rule
4. Mo formed best when atomic orbitals are similar in energy

Question 16

when wavefunction combine constructively vs destructively

Answer 16

1st: both wavefunctions are in phase
no new node created
contribute to bond construction
creates sigma bonding orbital

2st: wavefunction are in opp phase (up and below)
new node create
contributes to bond destruction
creates sigma star antibonding orbital