Molecular Orbitals

What is hybridisation?

Occurs when different types of atomic orbitals are mixed to generate a new set of atomic orbitals

What type of hybridisation occurs in alkanes?

• sp$ hybridisation (tetrahedral, 109.5° bond angles).

sp?2 hybridisation (trigonal planar, 120° bond angles).

What type of hybridisation occurs in alkynes?

sp hybridisation (linear, 180° bond angles).

How are sigma (o) bonds formed?

By end-on overlap of atomic orbitals.

How are pi (it) bonds formed?

By side-on overlap of atomic orbitals orbitals.

What determines bond type?

The difference in electronegativity between atoms.

What are the three types of bonds based on electronegativity difference?

• Non-polar covalent (small or zero difference).

• Polar covalent (moderate difference).

• lonic (large difference).

Why are alkanes unreactive?

They have non-polar bonds.

How do alkanes react with halogens?

Through free radical substitution (requires UV light).

What is homolytic fission?

Bond breaks evenly, forming radicals.

What is heterolytic fission?

Bond breaks unevenly, forming ions.

Which fission type is better for synthesis?

Heterolytic fission (fewer side products).

What is a nucleophile?

Electron-rich species that donates a pair of electrons.

What is an electrophile?

Electron-deficient species that accepts a pair of electrons.

What does a double-headed curly arrow represent?

Movement of an electron pair.

What does a single-headed curly arrow represent?

Movement of a single electron.

How are molecular orbitals formed?

By overlap of atomic orbitals.

What is HOMO?

Highest Occupied Molecular Orbital.

What is LUMO?

Lowest Unoccupied Molecular Orbital.

Why are most organic molecules colourless?

Their HOMO-LUMO energy gap absorbs UV light (not visible light).

What is a chromophore?

• A group of atoms that absorbs visible lig ht * naking molecules appear coloured.

. How does conjugation affect colour?

More delocalised electrons → smaller energy gap → absorbs visible light.

What is a conjugated system?

Alternating single and double bonds allowing electron delocalisation.

Why is carbon double bond shorter in length? Than c single

The pi bond pulls the carbon atom closer together, making its length shorter than a single