11-17-2025, 11:48 AM
Thread 3 — Chemical Bonding: Orbitals, Hybridisation & the Geometry of Molecules
How Electrons Shape the World Around Us
Everything in chemistry — reactivity, structure, colour, smell, hardness, conductivity —
comes from one thing:
How atoms share, exchange, or arrange their electrons.
This thread explores the deeper structure behind chemical bonding:
orbitals, hybridisation, molecular geometry, and why molecules have the shapes they do.
1. Atomic Orbitals — Where Electrons Live
Electrons don’t orbit like planets.
They exist in “clouds” called orbitals — regions of probability.
The main types:
• s-orbitals — spherical
• p-orbitals — dumbbell-shaped (px, py, pz)
• d-orbitals — cloverleaf or donut-shaped
• f-orbitals — complex multi-lobed shapes
These orbitals determine:*
• how atoms bond
• the angles they prefer
• the structure of molecules
[b]2. Covalent Bonds — Sharing Electrons
A covalent bond forms when orbitals from two atoms overlap and share electrons.
Key points:
• stronger overlap = stronger bond
• direction of the orbital = direction of the bond
• geometry is determined by orbital arrangement
Examples:
• H₂ forms from 1s–1s overlap
• O₂ forms from p–p overlaps (including π bonds)
• CH₄ forms from hybrid orbitals (sp³)
[/b]
[b]3. Hybridisation — Orbitals Blend to Fit the Molecule
Hybridisation is when atomic orbitals mix to create new bonding shapes.
There are three main types:
• sp → linear (180°)
• sp² → trigonal planar (120°)
• sp³ → tetrahedral (109.5°)
This explains:
• methane (CH₄) → sp³
• ethene (C₂H₄) → sp²
• ethyne (C₂H₂) → sp
Hybridisation is the hidden architecture of molecular geometry.
[/b]
[b]4. Sigma and Pi Bonds — Two Ways to Link Atoms
Covalent bonds come in two forms:
• Sigma (σ) bond — head-on overlap (stronger)
• Pi (π) bond — side-on overlap (weaker, only forms with p-orbitals)
Double bond = 1 sigma + 1 pi
Triple bond = 1 sigma + 2 pi
Pi bonds lock the geometry in place — this is why double bonds can’t freely rotate.
[/b]
[b]5. VSEPR Theory — Predicting Molecular Shapes
Electron pairs repel each other.
They arrange themselves to minimise repulsion.
This gives predictable shapes:
• 2 groups → linear (CO₂)
• 3 groups → trigonal planar (BF₃)
• 4 groups → tetrahedral (CH₄)
• 5 groups → trigonal bipyramidal (PCl₅)
• 6 groups → octahedral (SF₆)
These simple rules explain the shape of nearly every molecule on Earth.
[/b]
[b]6. Polarity — When Molecules Become Electric
A molecule is polar when:
• bonds have unequal electron sharing
• geometry does NOT cancel the charges
Examples:
• H₂O → polar
• CO₂ → non-polar (charges cancel)
Polarity controls:
• solubility
• boiling points
• reactivity
• biological function
[/b]
[b]7. Materials Science — Bonding Shapes the Macroscopic World
Everything about a material comes from bonding:
• diamonds (rigid network of sp³ carbon)
• graphite (layers of sp² carbon + delocalised electrons)
• metals (sea of electrons → conductivity)
• polymers (long covalent chains)
• ceramics (ionic + covalent networks)
Changing the bonding changes the entire material.
[/b]
[b]8. Why This Matters
Understanding bonding lets you predict:
• why molecules form
• how strong they are
• how they react
• their shape, colour, and function
• the properties of materials
Bonding is the foundation of all chemistry and materials science.
[/b]
Written by Leejohnston & Liora — The Lumin Archive Research Division
How Electrons Shape the World Around Us
Everything in chemistry — reactivity, structure, colour, smell, hardness, conductivity —
comes from one thing:
How atoms share, exchange, or arrange their electrons.
This thread explores the deeper structure behind chemical bonding:
orbitals, hybridisation, molecular geometry, and why molecules have the shapes they do.
1. Atomic Orbitals — Where Electrons Live
Electrons don’t orbit like planets.
They exist in “clouds” called orbitals — regions of probability.
The main types:
• s-orbitals — spherical
• p-orbitals — dumbbell-shaped (px, py, pz)
• d-orbitals — cloverleaf or donut-shaped
• f-orbitals — complex multi-lobed shapes
These orbitals determine:*
• how atoms bond
• the angles they prefer
• the structure of molecules
[b]2. Covalent Bonds — Sharing Electrons
A covalent bond forms when orbitals from two atoms overlap and share electrons.
Key points:
• stronger overlap = stronger bond
• direction of the orbital = direction of the bond
• geometry is determined by orbital arrangement
Examples:
• H₂ forms from 1s–1s overlap
• O₂ forms from p–p overlaps (including π bonds)
• CH₄ forms from hybrid orbitals (sp³)
[/b]
[b]3. Hybridisation — Orbitals Blend to Fit the Molecule
Hybridisation is when atomic orbitals mix to create new bonding shapes.
There are three main types:
• sp → linear (180°)
• sp² → trigonal planar (120°)
• sp³ → tetrahedral (109.5°)
This explains:
• methane (CH₄) → sp³
• ethene (C₂H₄) → sp²
• ethyne (C₂H₂) → sp
Hybridisation is the hidden architecture of molecular geometry.
[/b]
[b]4. Sigma and Pi Bonds — Two Ways to Link Atoms
Covalent bonds come in two forms:
• Sigma (σ) bond — head-on overlap (stronger)
• Pi (π) bond — side-on overlap (weaker, only forms with p-orbitals)
Double bond = 1 sigma + 1 pi
Triple bond = 1 sigma + 2 pi
Pi bonds lock the geometry in place — this is why double bonds can’t freely rotate.
[/b]
[b]5. VSEPR Theory — Predicting Molecular Shapes
Electron pairs repel each other.
They arrange themselves to minimise repulsion.
This gives predictable shapes:
• 2 groups → linear (CO₂)
• 3 groups → trigonal planar (BF₃)
• 4 groups → tetrahedral (CH₄)
• 5 groups → trigonal bipyramidal (PCl₅)
• 6 groups → octahedral (SF₆)
These simple rules explain the shape of nearly every molecule on Earth.
[/b]
[b]6. Polarity — When Molecules Become Electric
A molecule is polar when:
• bonds have unequal electron sharing
• geometry does NOT cancel the charges
Examples:
• H₂O → polar
• CO₂ → non-polar (charges cancel)
Polarity controls:
• solubility
• boiling points
• reactivity
• biological function
[/b]
[b]7. Materials Science — Bonding Shapes the Macroscopic World
Everything about a material comes from bonding:
• diamonds (rigid network of sp³ carbon)
• graphite (layers of sp² carbon + delocalised electrons)
• metals (sea of electrons → conductivity)
• polymers (long covalent chains)
• ceramics (ionic + covalent networks)
Changing the bonding changes the entire material.
[/b]
[b]8. Why This Matters
Understanding bonding lets you predict:
• why molecules form
• how strong they are
• how they react
• their shape, colour, and function
• the properties of materials
Bonding is the foundation of all chemistry and materials science.
[/b]
Written by Leejohnston & Liora — The Lumin Archive Research Division