chapter 10 p2 Flashcards
what does molecular orbital theory apply to?
Applies quantum mechanics to molecules, similar to
how it was applied to atoms
how does VB picture molecules?
VB pictures a molecule as a group of atoms bonded
through localized overlap of valence or hybrid
atomic orbitals
what does MO assume about orbitals?
MO assumes that orbitals are delocalized over the
whole molecule and occupied by electrons
how are MOS generated
You cannot solve Schroedinger’s equation exactly for
molecular orbitals
• Through a series of trial and errors we start with an
educated guess (trial function) and a computer program
tries to find the function that minimizes the energy of the
molecules orbitals
• MO’s can be mathematically approximated by the linear
combination of atomic orbitals (LCAO)
what are MOs similarities as AO?
Similar characteristics as AO
!Each can hold two electrons
!The square of the wavefunction gives the probability
density (shape)
what happens when two waves align and are in phase?
When two waves align and are in phase, the resulting wave is sum of the two waves !Constructive interference
what happens when two waves align out of phase?
• When two waves align out of phase, the resulting wave is the difference of the two wave !Destructive interference
how many phases do s orbitals have?
• s-orbitals only have
one phase
!Either (+) or (-)
how many phases do p oribtals have?
p-orbitals have two phases !(+) and (-) !Each lobe is a different phase
what do we use to approximate molecular orbitals?
We use a linear combination of atomic orbitals (LCAO) to
approximate molecular orbitals - combine atomic
orbitals of similar energy
when is a bonding oribtal formed? energy?
When the wave functions overlap constructively they
form a bonding orbital
• They are lower in energy than the original atomic orbitals
constructive interference
what happens when wave functions overlap destructively?
• When wave functions overlap destructively they form
anti-bonding orbitals
! A node is created between two atoms (no electrons)
! Energy of the orbital is higher than that of the original
atomic orbitals
look at mo diagram. what do the number of AOs equal?
The number of AOs combined always equals the
number of MOs formed
what is bond order?
Bond Order = difference between number of
electrons in bonding and antibonding orbitals
which electrons are considered for bond order? what does a higher bond order mean? bond order of 0?
- only need to consider valence electrons
- higher bond order = stronger and shorter bonds
- if bond order = 0, then bond is unstable compared to
individual atoms and no bond will form
formula for bond order
Bond Order = (# bonding electrons) - (# antibonding electrons) divided by
2
BO of He2? does it exist?
= 0
how many p orbitals can overlap end on end?
one, the other two cant
interactions of p orbitals: constructive end to end
The constructive end-to-end overlap of p-orbitals results
in the formation of a bonding σ2p MO
interactions of p orbitals: destructive end to end
The destructive end-to-end overlap of p-orbitals results in
the formation of an antibonding σ*
2p MO
interactions of p orbitals: constructive side by side
Constructive side-by-side
overlap of p-orbitals results in
the formation of π2p bonding
orbitals
interactions of p orbitals: destructive side by side
• Destructive side-by-side overlap
of p-orbitals results in the
formation of π*2p bonding
orbitals
energy of MOs
• MOs formed from 2s orbitals are lower in energy than MOs from from 2p orbitals !s orbitals are lower in energy than p orbitals
which orbitals overlap more extensively
Atomic p orbitals overlap
more extensively end to end
than side by side