133A inorganic - covalent bonding Flashcards
What would the result of this anti bonding be
Which one has highest and lowest electron density
Why are there no circles around the hydrogens?
their e- density is very hard to see as there is just one e- orbiting around the H nucleus/ 2e- shared between C-H
Why do all C-H bonds have the same enthalpy even though we would predict them to be different
hybridisation- makes 4 sp3 orbitals when the s of the hydrogens and p of the carbons overlap
What does an sp3 hybridised orbital look like
What does CH4 look like with the 4 sp3 hybridised orbitals (tetrahedral)
What does the CH3+ cation look like the 3 sp3 hybridised orbitals (trigonal planar)
Any carbon that is sp2 hybridised will aim for what bond angle
120°
need all the MO diagrams from my notes ‘atoms and molecules in bonding’/ got up to lecture notes 11
What are equations for the first second and third ionisation energies
What are the only electrons used for bonding
valenece electrons. In the case of CH4, the ‘core electrons’ (2s) are promoted to valence status
Why would the top bond be favoured
pi bonds are weaker than sigma bonds, which have better overlap
What would each of these look like once interacting to form a π bond
A shorter bond is stronger/weaker
stronger
What would these sp hybridised orbitals look like
What would two sp hybridised orbitals together look like
tetrahedral molecules have what hybridisation
sp3
trigonal planar molecules have what hybridisation
sp2
What do the bonds in a C2H4 molecule look like; what hybridisation does it have
-hybridised orbitals make σ bonds
-unhybridised orbitals make π bonds
Linear molecules have what hybridisation
sp
BeH2 is linear so it is sp hybridised. Show how the Be electrons become hybridised and then bond with the H orbitals
nitrogen in N2 looks like this. Show how an N2 molecule has a triple bond
Phosphorus can form PF5, so can make 5 bonds. Show how its electrons are excited to make 5 bonds with F of equal strength
sp3d (1 s , 3 p orbitals and 1 d)
What hybridisation/combination of orbitals would give octahedral geometry (6 bonds)
s+p+p+p+d+d= 6 orbitals of equal strength
Sulphur can form SF6 (form 6 bonds); how would its electrons be promoted to form 6 equal bonds
nitrogen here is sp2 hybridised. Show the new layout of nitrogens electrons to show it now has sp2 hybridisation
What would these two orbitals look like together when combined in phase
What are the 4 rules of molecular orbital theory
What do 2 s orbitals look like combining when out of phase
Which would be gerade and which ungerade
top- gerade (same when inverted)
bottom-ungerade (different when inverted)
Why is there a much bigger energy change when going to the anti bonding orbital compared to the bonding one
-σ goes down in energy to create more stable system
-bigger energy because the pairing of electrons takes some energy (get them in different spins)
-when σ* orbital is filled the bond will break, and energy needs to be put in to do this
Which is the atomic orbital diagram for 2 separate hydrogen, and which for bonded hydrogens in phase
What is the equation for bond order
What does it mean when something is diamagnetic
-not attracted to a magnetic field rather slightly repelled
all electrons in something are paired/ total spin in each orbital is therefore 0.
What does it mean when something is paramagnetic
one unpaired e- in an antibonding orbital/ orbital will have a net spin
-is attracted to a magnetic field
electrons that are alone in an orbital are called paramagnetic electrons
What does it mean if something has a bond order of 0<
the molecule can exist
What is the bond order of H2
2-0/2 = 1
-which means H2 has only 1 bond
How to prove wether Li2 exists
bond order= (4-2)/2= 1 so yes it can
Can [He2]+ exist
yes
Can [He2]+ exist
yes
Why do the interaction diagrams look different for H2 and Li2
H2 is overlapping of 1s orbitals, whereas lithium is 2s orbitals. The 2s orbitals are bigger and so there will be a less strong interaction between them than the 1s orbital/ Li-Li distance is much greater than H-H
Does Be2 exist
bond order= (2-2)/2= 0 so no
What would these make
What would these make
What would this make
Which orbital would be π-grade and which would be π-ungerade
gerade- same on inversion
ungerade- different on inversion
Even though all p orbitals are degenerate, why would the overlap of two Px orbitals be lower in energy that two Pz orbitals
σ bonds are stronger than π bonds
Draw a MO diagram for the mixing of all p orbitals
σ bonding orbital is lower in energy as it has better end-on overlap
draw a MO for F2
No mixing of AO’s of the same symmetry from a single F atom because there is a sufficient difference in energy between the 2s and 2p orbitals in F.
Draw MO for O2
the 2s and 2p orbitals are far enough apart that there is no mixing
Is O2 diamagnetic or paramagnetic
paramagnetic
If a bond length becomes longer, what will happen to the bond order
longer bond- lower bond order because bond is weaker
Why do we not get s and p orbital mixing in the diagrams for F2 and O2
F and O are very electronegative, so the energy difference between the 2s and 2p is large. The brown line is the s orbitals of the elements and the yellow is the p orbitals. We can see that the energy difference is large between the s and p orbitals
What changes about this standard diagram with the elements B,C and N
the σ and the π orbitals swap in energy
What is the MO diagram for B2
The 2s orbitals will mix with the σ bond from the two p orbitals, and the 2p orbitals will mix with the σ bond from the 2s shell
Draw the boundary surface diagrams for the 2σg orbital and the 2σ*u
Draw the boundary surface diagrams for the 3σg , 1πu, 1πg and the 3σu orbital
What is the MO diagram for C2
Only held together by a π bond, has no σ bond as it is cancelled out by the σ*
What is the MO diagram for N2
Held together by a 2 π bonds and a σ, the π bonds are stronger than the σ as they are lower in energy
If you mix 1s and 3p orbitals, how many orbitals do you end up with
3+1=4
in hybridisation p orbitals can mix, but in sp mixing (MO theory) they cannot. Why?
-hybridisation is where one orbital gains a little of another orbital (changing its shape) (e.g s and p making sp3 orbitals)
-In MO, orbitals need the right symmetry to mix
in hybridisation p orbitals can mix, but in sp mixing (MO theory) they cannot. Why?
-hybridisation is where one orbital gains a little of another orbital (changing its shape) (e.g s and p making sp3 orbitals)
-In MO, orbitals need the right symmetry to mix
What is the bond order of N2
3
Explain why across the table, bond distance gets shorter, then gets longer
bond distance gets shorter with bond order increasing/ when filling bonding orbitals BO= bonding-anti bonding
-therefore when filling anti-bonding orbitals BO will get lower and distance will get longer
how does the energy difference between s and p orbitals change as you move across the periodic table
energy difference gets bigger (why O and F do not have sp mixing but C,B,N do)
For diatomic molecules, which will be for C, B, N, O and F
first one B, C, N and last one O and F. O and F have no sp mixing because their s and p orbitals are far away in energy
Are s or p orbitals more distance sensitive
p- if you move the s orbitals away from each other they still have pretty good overlap, but a p overlap isn’t as strong and the bond may break
How is sp mixing effected by going down the periodic table
the highest s and p orbitals are not as separated so s-p mixing occurs in Cl2, Br2 and I2
homonucleur diatomic molecule- diatomic with same element
heteronucleur- different elements
isoelectric-same number of electrons
[C2]2- bond order= 3
C2 bond order= 2, so [C2]2- would be shorter
-if you added another electron to carbon
isoelectric- N2 (homonucleur)
What is a homonucleur molecule
are molecules composed of only one element (XX)
What is a heteronucleur molecule
molecule composed of atoms of more than one chemical element (XY)
What is the trend in bond order from
What is the equation for photon energy
PES- photoelectron spectroscopy
h= 6.6×10−34
hv= 6.6x10-34 x 5.13x10^15 = 3.39x10^-18
ans= I + 8.97x10^-19
so I = 2.5 x 10^-18 (need to put into KJ)
h= 6.6×10−34
hv = Ionization E + KE
In heteronucleur diatomic molecules (XY) the two atoms can have different electronegativities. What does this mean for MO diagrams if one is more electronegative than the other
more electronegative elements, valence orbital is lower in energy than for the more electropositive atom
This is the function for a bonding orbital. If Y is more electronegative than X, then would the value of CX or CY be bigger
CY would be larger than CX
This is the function for an antibonding orbital for a molecule XY. If Y is more electronegative than X, then would the value of C’X or C’Y be bigger
C’X is bigger
MO diagram for Li-H (XY diagram where on is more electronegative than the other)
H 1s orbital sits at lower energy than Li’s 2s because it is more electronegative
-LI-H bonding electron cloud (bottom) is distorted around H because its orbital energy is closer to H’s 1s orbital; this orbital has more contribution
-LI-H anti bonding electron cloud (top) is distorted around Li more because its orbital energy is much closer to Li’s 2s energy; this orbital has more contribution
What does the λ symbol mean in the wave function
The function with the λ infront of it is a much smaller contribution than a whole interner
(for the bonding orbital the electrons are more around H so Li will have λ)
(for anti bonding the electrons are more around Li so H will have λ)
MO diagram for HF (XY where one is more electronegative than the other)
Only the right p orbital interacts with the s orbital if they have the right symmetry.
Difference between the 2; same MO diagram, radical just has one less electron. OH- on left, OH* on right.
bond order of both is 1 so would have the same length
MO diagram for CO (XY) (very close to each other In periodic table)
s and p orbitals are close In energy so have mixing (π and σ orbitals swap places)
-HOMO is basically lone pair of electrons on the carbon
extra- can be a ligand and the HOMO on carbon are the donators
MO diagram for NO (XY) oxygen more electronegative
-paramagnetic and a radical
For some reason it is debated as to wether there is sp mixing although they are next to each other on the periodic table. But go with no mixing its less complicated
MO diagram for CN- (XY)
How to count valence electrons in an MO diagram
the number of electrons in the middle= 4
Say in exam questions with MO diagrams - “I have assumed sp mixing or I haven’t”
wether there is sp mixing doesn’t actually effect the bond order of something so it doesn’t really matter
how to draw NO+ lewis structure
valence electrons= 5+6 (-1 because its a +) = 10 valence electrons
1. put 2 electrons between them, then fill up oxygens shell and put 2 on N so you have 10 electrons
2. O has 8 valence, but N only has 4
3. move more electrons into the middle from oxygen until you have both octets
-10 valence electrons
- isoelectric with N2 or CO
Can NeO exist
yes (very rough diagram) This diagram assumes sp mixing but you could not assume that and swap the π2p and σ2p around
MO diagram for H3+ linear / think of this as H-H interacting with H+
Thinking about this as the H+ is going into the middle of one of these orbital phases.
-H3+ will have 2 electrons and it is assumed they come from H-H
The top H-H doesn’t interact because it has a nodal plane and the H+ doesn’t.
In phase and out of phase combinations
MO diagram for H3+ bent
This H3+ is a 3 centre 2 electron bond. How does this effect the bond order (a conventional bond is only over 2 atoms but this is one bond over 3)
bond order decreases. This bond order is 0.5
MO diagram for H3+ triangular
Does the u orbital symmetry have anything to do with the bonding between the atoms
no but you have to draw it out. That orbital only comes from the outside H-H atoms/ has nothing to do with holding the H3+ molecule together
MO for BeH2 linear/ think of the two H atoms as ligands that bond to Be in the middle
-1s orbital is too low in energy to interact but it would be on bottom of diagram
-Be has empty p orbitals that can still interact
-u and 2s are of same symmetry
-ALSO g and p are of same symmetry
-idk how there are electrons when the p didn’t have any but just look at interactions first then fill in with electrons
What is the bond order of BeH2
They are both 3 centre 2 electron bonds
still BO= 4/2= 2
Walsh diagram. On the right we have the full bonding (bottom), full antibonding (top), and the 2 outer H-H orbitals. As we go from 180° to bent, the orbitals change their energy. Why do they do this
to make the molecule more stable
Be able to draw a Walsh diagram for H3+ linear to bent
-Why is the triangle shape more stable/ goes down in energy from linear
-Why does the antibonding go down in energy
-Why does the H-H bonds go up in energy
-in linear bonding orbital there are 2 H-H bonds, but in the bent there are 3 H-H bonds which make it more stable,
-In antibonding, the H’s are in phase and as you bend them they get closer and form a bonding interaction which brings the energy down
-H-H bonds are out of phase and closer together in a triangle which makes an antibonding interaction which is high in energy
Walsh diagram for H3+ linear and bent. Why are the two top orbitals in the bent configuration degenerate
degenerate because amount of bonding interactions is the same in them
1. H-H has one antibonding interaction say =-1
2. H-Be-H has 2 antibonding interactions and 1 bonding interaction which also makes =(1-2) =-1
Why when moving across the periodic table do molecules the element can make get lower in energy
Shape gets more bent which shape is lower in energy
What is the equation for electronic state (singlet/ triplet)
This is CH2 in its triplet state
electronic sate= no. unpaired electrons + 1
if you have no unpaired e it is a singlet
MO diagram for H20
1) do all orbitals as you would expect
2)But the upright p orbital does not like this as it is close to the H and repels the electrons there
3) HOMO and LUMO will have sp mixing so in final diagram HOMO will go down in E and LUMO will go up
What is this as an MO diagram
How many valence electrons in BH3
B= 3 + 1x3 = 6
MO diagram for BH3/ with multimolecular diagrams consider the orbitals in 2 parts
Boron= 5 electrons total
The two interactions with the p orbitals and the H’s will be degenerate in energy
-The Pz orbital doesn’t have the right symmetry to interact so will stay an empty p orbital- this is why BH3 is very reactive
MO for NH3 (nitrogen more electronegative)
nitrogen is lower down as it is more electronegative
-HOMO and LUMO interact so HOMO goes down in E and LUMO goes up (to make the lone pair above nitrogen same in H20)
CH4 MO diagram c=2p2
bond order= 1
think its 8/2 = 4 but each bond is over 4 atoms so its 4/4=1
SiH4 MO diagram
Why do HOMO LUMO gaps get smaller as you go down a group (say bonding H to Be, Mg, Ca etc)
As go down group atoms become bigger so overlap with H will get poorer. The bonds get weaker, more reactive
CO2 MO diagram
C= 2s2, 2p1
O= 2p4
1) N2+, an electron is removed, so the bond order decreases to 2.5/ bond is weaker and longer.
2) N2–, an electron is added to the 1πg* antibonding orbital, so the bond order also decreases to 2.5/ bond is weaker and longer.
3) N22–, a second electron is added to the 1πg* antibonding orbital; bond order is 2/ bond is weaker and longer
Increased electron-electron repulsions contribute to this being longer than expected.
