Intramolecular vs Intermolecular Forces: The Difference

The names look almost identical, and that one syllable — intra vs inter — trips up thousands of students every exam season. Get it straight once and a whole chunk of chemistry (boiling points, states of matter, why ice floats) clicks into place.

The short answer: intramolecular forces are the bonds inside a molecule that hold its atoms together (ionic, covalent, metallic) — they're strong. Intermolecular forces are the weaker attractions between separate molecules. The prefixes are the whole trick: intra means "within," inter means "between."

Quick comparison at a glance


Feature Intramolecular forces Intermolecular forces
Where they act Within one molecule (atom to atom) Between separate molecules
What they are Ionic, covalent, metallic bonds Dispersion, dipole–dipole, hydrogen bonds
Relative strength Strong (~100–1000 kJ/mol) Weak (~1–40 kJ/mol)
What breaking them means A chemical reaction A change of state (melt/boil)
Example The O–H bonds in H₂O The attraction pulling H₂O molecules together

Notice the strength gap in that table — it's the key to the most common exam question of all.

What intramolecular forces are

Intramolecular forces are just the chemical bonds you already know, seen from a "what holds this molecule together" angle:

  • Covalent bonds — shared electrons (the O–H bonds in water).
  • Ionic bonds — transferred electrons and the attraction between the resulting ions (Na⁺ and Cl⁻ in salt).
  • Metallic bonds — a lattice of metal ions in a sea of electrons.

These are strong. Breaking them means changing the actual chemical identity of the substance — that's a chemical reaction, not just warming something up.

What intermolecular forces are

Intermolecular forces (IMFs) are the gentler attractions between whole molecules. In rising order of strength they are:

  • London dispersion forces — tiny, fleeting attractions present in every molecule.
  • Dipole–dipole forces — between polar molecules, δ+ of one lining up with δ− of the next.
  • Hydrogen bonds — an especially strong dipole–dipole attraction when H is bonded to N, O, or F.

Even the strongest IMF is far weaker than a covalent bond. But IMFs are what decide whether a substance is a gas, liquid, or solid at room temperature, and how high its boiling point is.

The question that matters: what breaks when water boils?

This is the classic trap. When you boil water, the molecules fly apart into steam — but the water molecules themselves survive. Steam is still H₂O.

So boiling breaks the intermolecular forces (the attractions between molecules), not the intramolecular O–H bonds inside them. To break those covalent bonds you'd need far more energy — enough to split water into hydrogen and oxygen, a genuine chemical reaction. Melting and boiling only ever overcome the weaker intermolecular forces.

Worked examples

Decide which type of force each describes:

  • The bond between H and O in a water molecule → intramolecular (covalent).
  • The attraction that makes water droplets bead up → intermolecular.
  • The force broken when ice melts → intermolecular.
  • The force broken when you electrolyse water into H₂ and O₂ → intramolecular (a chemical change).
  • The attraction between two neighbouring CO₂ molecules in dry ice → intermolecular.

Common mistakes to avoid

  • Thinking boiling breaks bonds. Boiling overcomes intermolecular forces only. The covalent bonds inside each molecule stay intact.
  • Mixing up the prefixes. Intra = within (like an intranet, inside one organisation). Inter = between (like the internet, between many). Anchor it to a word you know.
  • Assuming intermolecular forces are just "weak bonds." They're not chemical bonds at all — they're attractions between separate particles, in a completely different strength league.

FAQ

What is the main difference between intramolecular and intermolecular forces?
Intramolecular forces hold atoms together within a molecule and are strong; intermolecular forces attract separate molecules to each other and are much weaker.

Which is stronger, intramolecular or intermolecular forces?
Intramolecular forces (the bonds) are far stronger — often 10 to 100 times stronger than the intermolecular attractions between molecules.

What forces are broken when a substance boils?
Only the intermolecular forces. The molecules separate but stay whole, which is why steam is still water.

Are intermolecular forces types of bonds?
No. They're attractions between molecules, not chemical bonds. Only intramolecular forces (ionic, covalent, metallic) count as bonds.

The takeaway

Intra is inside, inter is between. Intramolecular forces are the strong bonds holding a molecule's atoms together; intermolecular forces are the weaker attractions pulling whole molecules toward one another. Melting and boiling break the weak ones; only a chemical reaction breaks the strong ones.

Next up → [Hydrogen Bonds vs Van der Waals Forces] — a closer look at the intermolecular family. See also [What Is a Polar Molecule?] and [Ionic vs Covalent Bonds].

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