Molecular Orbitals Flashcards
What can orbitals be used to explain?
The bonding between atoms
What are atomic orbitals?
The volume of space that the electron of an atom is likely to be found
What happens when atomic orbitals overlap?
They combine to form molecular orbitals
What are sigma bonds?
The end on overlapping of orbitals
What governs the type of intermolecular bonding?
The shape of the molecular orbital
How are non-polar bonds formed?
When two atoms of the same element bond
What can be said about the molecular orbitals formed in non-polar elements?
The molecular orbital formed from overlapping atomic orbitals is symmetrical around a mid-point where the bonding electrons are most likely to be found
What is a polar covalent bond?
When there is a large difference between the electronegativities of the two elements involved in the bond
What can be said about the molecular orbits in polar covalent bonds?
The bonding molecular orbitals will be asymmetrical
What happens when ionic bonds form?
There is extreme asymmetry
What does hybrid theory assume?
That the 2s and 2p orbitals of carbon atoms combine to form four degenerate orbitals
What are the hybrid orbitals formed from 1 s orbital and 3p orbitals called?
They are called sp³ orbitals
What happens in alkanes?
All four hybrid orbitals are used to form sigma bonds
What can be said about sigma bonds?
They allow free rotation around orbitals
How are C-C bonds in alkanes formed?
From the overlapping of sp³ orbitals forming sigma bonds
How many sigma bonds are in ethane?
7
What does an electron being promoted to higher energy levels result in?
The formation of 3 hybrid orbitals, with one remaining unhybridised 2p orbital
What is bonding in alkanes due to?
hybridisation
What are the hybrid orbitals from one s orbital and two p orbitals called?
sp² orbitals
What is the angle between sp² orbitals?
120 degrees
What is a pi bond?
The sideways overlap of two parallel atomic orbitals
What is the comparison between sigma and pi bonds?
Pi bonds are weaker than sigma bonds
What bonding orbitals are present in C-C bonds?
1 sigma bond
What bonding orbitals are present in C=C bonds?
1 sigma and 1 pi
What bonding orbitals are present in C≡C bonds?
1 sigma and 2 pi
What are isomers?
Molecules with the same chemical formula but different structural formula
What can be said about structural isomers?
They have different physical and chemical properties
What are the two types of stereoisomerism?
- geometric isomerism
* optical isomerism
What is geometric isomerism a result of?
A lack of rotation around a bond
What is a cis isomer?
cis means the functional group is on the same side of the C=C
What is a trans isomer?
When the functional group is on opposite sides of the C=C bond
Why do trans isomers have higher mpts?
As these molecules can pack more closely together thus maximising the intermolecular forces
Why do cis molecules have higher bpts?
Because of their PD-PD interactions
What are the types of geometric isomerism?
- cis isomerism
* trans isomerism
Why are cis isomers more readily dehydrated than trans isomers?
because of the close proximity of the OH groups
What are optical isomers?
They are mirror images of each other but are not superimposable
What does a tetrahedral molecule have the potential to be?
chiral
How does chirality occur?
when the middle atom is attached to four different groups
What does a polariser allow?
Light vibrating in only a single plane to pass through them
What are enantiomers?
Another term used to describe optical isomers
What is a racemic mixture?
One which contains equal amounts of each enantiomer
What type of hybridisation is present in alkynes?
sp hybridisation
What type of hybridisation is present in alkenes?
sp² hybridisation
What type of hybridisation is present in alkanes?
sp³ hybridisation
What does the combination of two atomic orbitals result in?
the formation of a bonding and an antibonding orbital
When electrons fill bonding molecular orbitals, what do they leave behind?
Higher energy antibonding orbitals unfilled
How many groups are changed in enantiomers ?
Only 2.
