09/04/2026
Why do some compounds melt or boil at super high temperatures while others don’t? 🤔
It all comes down to bonding and inter molecular forces!
🔬 Silicon dioxide (SiO₂) has a giant covalent structure, a strong 3D network where many covalent bonds must be broken. That’s why it has extremely high melting and boiling points.
💨 Sulfur dioxide (SO₂), on the other hand, is a simple molecule. Only weak intermolecular forces (like van der Waals and dipole-dipole) need to be overcome, so it melts and boils at much lower temperatures.
💧 Ammonia (NH₃) forms strong hydrogen bonds because nitrogen is highly electronegative, giving it higher boiling points than expected.
🌫️ Phosphine (PH₃) is much less polar, so it only has weak dipole forces between molecules, meaning lower boiling points.
👉 Strong bonds = more energy needed
👉 Weak forces = less energy needed
Chemistry is all about how atoms stick together! 🧪✨
Now, here’s how to turn it into a powerful revision tool 👇
🧠 Step 1: Start with the central idea
Put in the middle of your mind map:
👉 Intermolecular Forces & Structure
🔗 Step 2: First branches (big categories)
Split into two main paths:
Giant Covalent Structures
Simple Molecular Substances
🧱 Step 3: Add your examples
1️⃣ Giant Covalent
Example: SiO₂
Strong covalent bonds throughout lattice
No intermolecular forces (it’s one big structure)
✅ Very high melting/boiling point
👉 Key idea: You break bonds, not forces
2️⃣ Simple Molecular
Split this further 👇
💨 Weak intermolecular forces
Example: SO₂
Has dipole-dipole + van der Waals
❗ Still much weaker than covalent bonds
✅ Low melting/boiling point
💧 Hydrogen bonding
Example: NH₃ (ammonia)
Nitrogen is highly electronegative
Forms hydrogen bonds
✅ Higher boiling point than expected
🌫️ Very weak forces
Example: PH₃ (phosphine)
Low polarity
Only van der Waals forces and dipole attractins
✅ Very low boiling point
⚡ Step 4: Add a comparison rule (this is the exam gold)
Make a small box in your mind map:
👉 Strength order:
Covalent bonds >> Hydrogen bonds > Dipole-dipole > van der Waals
🎯 Step 5: Turn it into a quick recall trick
From this one question, you train your brain to automatically think:
What is the structure?
What forces/bonds are present?
How strong are they?
→ Predict melting/boiling point
🔥 Why this works so well
Instead of memorizing facts like:
“NH₃ has higher boiling point”
“SiO₂ is high melting”
You understand the reason behind everything!!
