Structure and Bonding in Organic molecules Flashcards
Describe the shape of a 1s orbital
The 1s orbital is spherically symmetrical with no nodes
What is a node
Is a region where the probability of finding an electron is zero
What is the maximum occupancy of an orbital
2 electrons
Do 2s orbtials have nodes
Yes they possess a spherical node and is higher in energy than the 1s node
What is a change in phase
Moving from inside the node to outside the node
Describe the 2p orbitals
They are formed of two lobes with a nodal plane between the two lobes
This type of orbital is not spherical and possesses a planar node at the nucleus
There are three 2p orbitals occupying different axes of cartesian coordinates
How do we make molecular orbitals
We combine atomic orbitals to give molecular orbitals
Atomic orbitals (like waves) can be combined in a out of phase
What happens if you combine two atomic orbitals in phase
For example like two waves that are in phase combine, the resultant wave is larger
Constructure
Forming a bonding molecular orbital
What happens if you combine two atomic orbitals out of phase
For example, when two waves that are out of phase combine, the waves cancel each other out
Destructive
Forming an antibonding molecular orbital
How would you draw the molecular diagrams for the combining of atomic orbitals to form molecular orbitals?
The valence electrons for the atom go on the outside
The molecular orbitals formed from combing atomic orbitals go on the inside
Energy of the bonding orbital is lower than the energy of the two antibonding orbitals
Both electrons from the hydrogen atom in this case move into the lower energy bonding orbital and the antibonding orbital is empty
How would we break a bond (e.g. between H2) in terms of it’s orbitals
We must promote one electron to the antibonding orbital
This process regenerates the two separate hydrogen atoms, which can then diffuse apart
(However in practice it is difficult for hydrogen as the energy gap between bonding and antibonding orbitals is large)
A sigma bond is formed how
what two things is it made up from
End-on overlap between two s orbitals, end-on overlap between an s and a p orbital, end-on overlap between two p orbitals
made up of sigma bonding and sigma * (antibonding) orbitals
Orbitals and *Orbitals are symmetrical by rotation around the bond axis
describe the appearance of s orbitals combining in and out of phase (end on)
This interaction forms a sigma bond (end on)
Describe the appearance of p orbitals combining in and out of phase (edge-on)
This forms a Pi bond
there is no cylindrical symmetry
What are some conditions which must be met in order for atomic orbitals to combine to form molecular orbitals
- AOs of similar energy
- AOs of similar size
- AOs of appropriate symmetry
Why must atomic orbitals combine with a similar size
Why must atomic orbitals combine with appropriate symmetry
