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Explain résonance structures
When a molecule has multiple valid VSEPR structures, those are resonance structures
the actual structure is intermediate between the pair.
It’s called a resonance hybrid
Bond length/order and bond density is an average of the two structures
There must be at least a PI bond present, as that the delocalised electron which goes from one bond to the other.
Occurs when there are adjacent atoms of equivalent electro negativity
Evidence for resonance structure of benzene
all bond angles and lengths are the same
Enthalpy of hydrogenation is lower than expected ( only 210 instead of 360). More stable bc of pi bonds
Saturation tests; it didn’t react as alkene would react; didn’t turn bromide water colourless as. Doesn’t undergo addition reaction with bromide p, but substitution
Expanded octets
only smaller atoms, period 3 or above
The energy level of 3p and 3d is very similar
Higher VSEPR
Fuck VSEPR - use drawn flash cards or kognity
Formal charge formula
Number of valence electrons - number of lone electrons - nr of electrons in bonding pairs
The closer to 0 the more stable
Can happen with coordination bond
For an ion net formal charge has to be same as overall chance and for a molecule it has to be 0
Sigma bond
Head on overlap of orbitals; ie s-s, p-p, s-p.
Single bonds are Always sigma
Stronger than pi, as there is only one electron dense region on the inter nuclear axis
Pi bond
sideways overlap of p orbitals
Different Axial plane than sigma bonds as the electrons repel each other
These are all the extra bonds after a single bond
They are weaker than sigma bonds and are first to break, as they are located further away from the positive charge of the nucleus
If there are multiple Pi orbitals close to each other, the electrons are delocalised and can move through there
Excitation of electron
Moving from ground state to excited state by energy absorption
Hybridisation
mix of atomic orbitals to produce hybrid orbitals of intermediate energy; ie between S and between P
total energy hasn’t changed -, but has been equally redistributed
carbon SP3 hybridisation
one electron from S orbital and 3 from P blend together
only single bonds as no P orbitals left
carbon SP2 hybridisation
one electron from S orbital and 2 from P blend together
double bonds can be formed as a P is left
carbon SP hybridisation
one electron from S orbital and one from P blend together
triple bonds can be formed as there still are 2 P orbitals left