Molecular Orbitals Flashcards
What does covalent bonding between atoms involve?
the overlap of atomic orbitals (s,p orbtials) to form molecular orbitals (π σ)
How are molecular orbitals formed?
By the linear combination of atomic orbitals
What maximum number of electrons can each molecular orbital hold?
2
What are the two types of molecular orbitals?
bonding and antibonding
What are molecular orbitals formed by the overlap of s orbitals denoted with?
sigma (σ)
Why is it called a bonding molecular orbital?
the electrons in this orbital spend most of their time in the region directly between the two nuclei
Why is it called a σ molecular orbital?
it looks like an s orbital when viewed along the bond axis
How is a bonding molecular orbital made?
by adding the mathematical functions for the atomic orbitals that come together to form the molecule
How is an antibonding molecular orbital made?
by subtracting one functiokn from the other
Why is it called an antibonding molecular orbital?
the electrons spend most of their time away from the region between the two nuceli.
What is an antibinding molecular orbital denoted with?
σ*
How are electrons added to molecular orbitals?
one at a time, starting with the lowest energy molecular orbital
In terms of a H2 molecule and its molecular orbital diagram, talk about its stability.
The diagram suggests that the energy of a H2 molecule is lower than that of the H atoms. As a result, the H2 molecule is more stable than a pair of isolated H atoms.
Give the 3 possible orbital combinations that form σ bonds.
- s orbital + s orbital
- s orbital + p orbital
- p-orbital + p orbital (‘head-on’ overlap)
How are π bonds formed?
by the lateral overlap of p orbitals
Why are they called π molecular orbitals?
They look like p orbitals when viewed along the line of the bond
When carbon forms bonds, what happens to one of the 2s electrons?
it is promoted to a higher energy 2p orbital
When carbon forms bonds, what happens to the 2s and three 2p orbitals?
they combine to make 4 equivalent orbitals called sp3 hybrid orbitals
How many electrons does each sp3 hybrid orbital hold?
1
What arrangement do the 4 sp3 hybrid orbitals take up?
tetrahedral
For methane, what does each sp3 hybrid orbital on carbon do?
overlap with a 1s orbital of H to give 4 equivelant sigma (σ) bonds
What are all 7 of the bonds in ethane?
σ bonds
What are σ bonds found in?
all saturated molecules
What is sp3 hybridisation found in?
all saturated molecules
For bonding in alkenes, what kind of hybridisation occurs?
sp2 hybridisation
Describe sp2 hybridisation.
It is the combination of the 2s orbital with 2 2p orbitals giving three equivelent sp2 hybrid orbitals
What arrangement do the 3 sp2 hybrid orbitals adopt?
trigonal planar
How does the unhybridised p-orbital sit?
sits at 90’ to the planar structure
Describe what happens to 2 sp2 hybrid orbitals in ethene?
they overlap to form a σ bond
Describe what happens to the p orbitals on adjacent C atoms in ethene?
they overlap to form a π bond
In ethene, what does the double bond consist of?
a σ and a π bond
What do all double bonded C atoms show?
sp2 hybridisation
Why are π bonds weaker than σ bonds?
the electrons in the bond are not localised between the nuclei
What will the shape of the molecular orbital formed from overlapping atomic orbitals govern?
the type of intermolecular bonding that is observed
Non-polar/ pure covalent bonds are formed between two atoms of the same element, or two atomd with a very low difference in electronegativities. Describe what effect this has on the molecular orbitals.
The molecular orbital formed from overlapping atomic orbitals is symmetrical around a mid-point where the bonding electrons are most likely to be found
For when there is a large difference in electronegativities, describe the shape of the bonding molecular orbital.
asymmetrical
