L6 - Hybridisation of carbon

What is a covalent bond?

A pair of electrons shared between 2 atoms → strong, directional attractive force

How many covalent bonds does carbon typically form?

4 covalent bonds by sharing its 4 outer-shell electrons

What are sigma (σ) bonds?

End-to-end overlap of atomic orbitals; first bond formed between 2 atoms; max 1 σ bond between 2 atoms

What are pi (π) bonds?

Side-to-side overlap of p orbitals; occur in addition to a σ bond in double/triple bonds

How many π bonds can form between two atoms, and which orbitals form them?

Only p orbitals form π bonds; adjacent atoms can form π bonds in addition to the σ bond

What is carbon's ground-state electronic configuration?

1s²2s²2p²

Why does carbon form 4 covalent bonds?

Its 2nd shell has 4 electrons but is energetically favourable with 8 → shares its 4 outer electrons

What types of multiple bonds can carbon form?

Double and triple bonds; e.g. alkenes, carbonyls and alkynes

What hybridisation occurs when carbon forms 4 σ bonds?

sp³ hybridisation

What is the orbital composition of sp³ hybridisation?

1 s + 3 p orbitals → 4 sp³ hybrid orbitals

What are the geometry and ideal bond angle of sp³ carbon?

Tetrahedral; 109.5°

What hybridisation occurs when carbon forms 3 σ and 1 π bond?

sp² hybridisation → 3 sp² orbitals + 1 unhybridised p orbital

How do sp² orbitals and the remaining p orbital form bonds?

sp² orbitals form σ bonds; remaining p orbital overlaps with another p orbital to form a π bond

What are the geometry and ideal bond angle of sp² carbon?

Planar arrangement; 120°

What is the effect of a π bond on rotation around a double bond?

It prevents rotation around the double bond

What hybridisation occurs when carbon forms 2 σ and 2 π bonds?

sp hybridisation → 2 sp orbitals + 2 unhybridised p orbitals

How does sp hybridisation allow a carbon to form a triple bond?

2 sp orbitals form σ bonds; 2 remaining p orbitals form 2 π bonds

What are the geometry and ideal bond angle of sp carbon?

Linear; 180°

How does s-character differ between sp, sp² and sp³ orbitals?

sp = 50% s; sp² ≈ 33% s; sp³ = 25% s

Why are sp-hybridised bonds shorter than sp²/sp³ bonds?

Greater s-character → orbitals are smaller and closer to the nucleus

What effect does sp hybridisation have on acidity?

Greater s-character makes compounds more acidic; e.g. alkyne C–H vs alkane C–H

What determines carbon's hybridisation state?

The number of σ and π bonds it forms → orbitals hybridise to maximise bonding energy/orbital overlap

What happens to the number of orbitals/electrons during carbon hybridisation?

Number of orbitals/electrons stays constant; shape and energy of hybridised orbitals change

What is the relationship between carbon hybridisation and bond rotation?

sp³ single bonds allow rotation; sp² π bonds restrict rotation around double bonds

How does carbon bonding differ in sp³, sp² and sp hybridisation?

sp³: 4σ; sp²: 3σ+1π; sp: 2σ+2π