Bonding Molecular orbital theory - molecular orbital theory

Question 1

constructive waves definition

Answer 1

waves which overlap in the same phase which produce a greater amplitude.

Question 2

destructive waves definition

Answer 2

waves which overlap in different phases which produce no amplitude.

Question 3

how are antibonding molecular orbitals formed

Answer 3

The electrons in atomic orbitals will act as deconstructive waves and overlap out of phase, producing a higher energy orbital where electrons will fill after the bonding orbital.

Question 4

how are bonding molecular orbitals formed

Answer 4

The electrons in atomic orbitals will act as constructive waves and overlap in phase, producing a lower energy orbital where electrons will fill before the antibonding orbital.

Question 5

wave function of bonding molecular orbital

Answer 5

ψ = CaXa + CbXb

Question 6

wave function of molecular orbitals

Answer 6

ψ* = CaXa - CaXb

ψ = CaXa + CaXb
c stands for weighting co efficient.
x stands for atomic orbital wave function.
ψ stands for molecular orbital wave function.

Question 7

how do you show that an orbital is an antibonding molecular orbital

Answer 7

you use a *

Question 8

antibonding molecular orbitals features

Answer 8

antibonding molecular orbitals will always contain an extra nodal plane than bonding molecular orbitals due to destructive waves overlapping to produce a part of the wave function which will pass through 0.

Question 9

σ bond linear combination of atomic orbitals

Answer 9

same sign s orbitals form σg
opposite sign s orbitals will form σu*

Question 10

g meaning

Answer 10

g stands for even - if the orbital has y axis symmetry it will be even

Question 11

u meaning

Answer 11

u stands for odd - if the orbital has half turn rotational symmetry it is odd.

Question 12

u orbitals

Answer 12

σ and π*
antibonding sigma and bonding pi

Question 13

g orbitals

Answer 13

σ* and π
bonding sigma and antibonding pi

Question 14

numerical proof for u and g

Answer 14

if when +orbital = (x,y,z), -orbital = -(x,y,z) it is u
if when + orbital = (x,y,z), - orbital = (x,y,z) then it is g.

Question 15

when would you use u and g

Answer 15

when you have homonuclear atoms bonding with the same type of orbital.

Question 16

bond order formula

Answer 16

(number of electrons in bonding orbitals - number of electrons in antibonding orbitals) / 2

Question 17

which molecular orbitals fill first

Answer 17

bonding molecular orbitals fill first since they are lower energy.

Question 18

what does a bond order of 0 show

Answer 18

the molecular structure will not be possible.

Question 19

bond order rules

Answer 19

as the bond order increases the bond strength increases and bond length will decrease.

Question 20

oxidation of molecules effect on bond order

Answer 20

oxidation is a loss of electrons, which will mean that electrons will be lost from the HOMO, this will alter the bond order.

Question 21

reduction of molecules effect on bond order

Answer 21

reduction is a gain of electrons, so electrons will fill the LUMO.

Question 22

LUMO

Answer 22

the lowest unoccupied molecular orbital

Question 23

HOMO

Answer 23

the Highest occupied molecular orbital.

Question 24

SOMO

Answer 24

A singularly occupied molecular orbital

Question 25

what does a SOMO mean

Answer 25

It means that the HOMO and the LUMO are the same orbital, meaning electrons will be lost and gained from the same orbital.

Question 26

rule for orbitals considered in bond order and molecular orbital diagrams

Answer 26

always just use valence orbitals
eg: if we use fluorine we only consider 2s and 2p orbitals.

Question 27

what does a squiggly line mean in molecular orbital diagrams

Answer 27

the squiggly line will represent the core orbitals which don’t matter in the final calculation.

Question 28

linear combinations of atomic orbitals for p orbitals

Answer 28

same sign pz atomic orbitals will form σg
opposite sign pz atomic orbitals will form σu*
same sign pxy atomic orbitals will form πu
different sign pxy orbitals will form πg*

Question 29

molecular orbital diagrams using p orbitals steps

Answer 29

1. write out electronic configuration of atoms.
2. identify the number of valence electrons.
3. set out molecular orbital energy chart.
   fill in electrons using Aufbau and hunds rule.
   calculate bond order.

Question 30

labelling orbitals in MO diagrams

Answer 30

give every molecular orbital a number starting with 1 being the lowest energy π and σ orbitals.

Question 31

bond strength formula

Answer 31

v = 1/2π x sqrt(k/μ)
v is vibrational frequency
k is the force constant
μ is the reduced mass

Question 32

linear combinations of atomic orbitals for s and p overlap

Answer 32

same sign pz and s will result in a σ bonding orbital.
opposite sign pz and s will result in a σ antibonding orbital.
px or py with an s orbital will result in no orbital being formed due to the difference in symmetry between the orbitals meaning that the constructive and destructive overlap of the waves will cancel each other out.

Question 33

orbital energy rule

Answer 33

As you go along a period the positive charge of the nucleus, which will result in a greater difference between the σ and π orbitals

Question 34

elements where σ and π orbitals will mix

Answer 34

boron, carbon and nitrogen due to low energy differences between 5σg and 1πu

Question 35

elements where σ and π will not mix

Answer 35

fluorine, oxygen and neon due to higher energy gap between the 5σg and 1πu orbitals.

Question 36

rule for extra contribution of bonding to molecular orbital diagrams

Answer 36

pz and s orbitals will contribute towards all σ orbitals.
px and py will contribute towards all π bonds.

Question 37

rule for π orbitals energy

Answer 37

π orbitals energy wont change only the σ orbitals energy changes.

Question 38

electronegativity on heteronuclear diatomic Molecular orbitals

Answer 38

the more electronegative atom will have lower energy orbitals and therefore contribute more towards the bonding molecular orbital.

the electropositive atom will have greater energy orbitals and contribute more towards the antibonding ,molecular orbital.