Chemistry revision sheets

56 printable sheets for general chemistry revision. Three volumes in US Letter and A4. $9.99 before applicable tax.

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Lone Pair vs Bonding Pair: What's the Difference?

You've drawn the Lewis structure. Every atom has its octet, the dots are all placed — and then the question asks for the shape, and suddenly it matters which pairs are which. Getting lone pairs and bonding pairs straight is the single step between a correct dot diagram and a correct molecular shape.

The short answer: a bonding pair is a pair of electrons shared between two atoms, holding them together — it's what a line in a structural formula represents. A lone pair is a pair of electrons sitting on one atom only, bonded to nothing, and because it's held by a single nucleus it spreads out more and pushes harder on everything around it.

Quick comparison at a glance

FeatureBonding pairLone pair
Also calledShared pair, bond pairNon-bonding pair, unshared pair
How many nuclei attract itTwoOne
Shown in a structure asA line (or two dots between atoms)Two dots on a single atom
Shape in spacePulled tight between two nucleiFatter and closer to its own atom
Repulsion strengthWeakestStrongest
Effect on bond angleSets the ideal angleSqueezes the angle smaller
Counts as an electron domain?Yes (a double or triple bond still counts once)Yes
Visible in the molecular shape?Yes — the atoms you can seeNo — invisible, but it still bends the molecule
Chemical roleHolds the molecule togetherSite of basicity, hydrogen bonding, nucleophilic attack

What a bonding pair is

A bonding pair is two electrons shared between two atoms. Both nuclei pull on the same pair, and that shared attraction is what a covalent bond actually is. When you draw H–O–H, each of those lines stands for one bonding pair.

Because two nuclei are pulling from opposite sides, a bonding pair gets stretched into a narrow region between the atoms. It's pinned down. That matters for the next section: a pinned-down pair doesn't have much room to shove its neighbours around.

One thing that trips people up: a double bond contains two bonding pairs and a triple bond contains three, but when you're working out shape, all of them together count as one region of electron density — one "domain" — because they all sit between the same two atoms. In CO₂, each C=O is two bonding pairs, but carbon has only two domains, so the molecule is linear.

What a lone pair is

A lone pair is two valence electrons that belong to one atom and are not shared with anything. Oxygen in water has two of them. Nitrogen in ammonia has one. Chlorine in HCl has three.

Only one nucleus is attracting a lone pair, so nothing is stretching it out sideways. It stays bunched close to its own atom and spreads out more in angular terms — it takes up a wider slice of the space around the central atom than a bonding pair does. That's the whole reason lone pairs matter for shape:

lone pair–lone pair > lone pair–bonding pair > bonding pair–bonding pair

That repulsion order is the one line worth memorising. It explains a run of bond angles you'll be asked about again and again:

  • CH₄ — 4 bonding pairs, no lone pairs → perfect tetrahedron, 109.5°
  • NH₃ — 3 bonding pairs, 1 lone pair → the lone pair presses the N–H bonds together, 107°
  • H₂O — 2 bonding pairs, 2 lone pairs → two lone pairs press harder still, 104.5°

Same tetrahedral arrangement of four domains all three times. The angle shrinks by roughly 2–2.5° for each lone pair you add.

How to count them from a Lewis structure

  1. Total the valence electrons for every atom (add one per negative charge, subtract one per positive charge).
  2. Draw a single bond from the central atom to each outer atom — that's 2 electrons used per bond.
  3. Complete the octets of the outer atoms with lone pairs.
  4. Anything left over goes on the central atom as lone pairs. If the central atom is short of an octet, pull an outer lone pair in to make a double bond.
  5. Count domains on the central atom: number of attached atoms + number of lone pairs on it.

Try H₂O. Valence electrons: 6 (O) + 2 × 1 (H) = 8. Two O–H bonds use 4, leaving 4 — two lone pairs on oxygen. Oxygen therefore has 2 bonding domains and 2 lone pairs, four domains total.

Worked examples

Predict the number of bonding pairs and lone pairs on the central atom before you read the answer.

  • NH₃ → 3 bonding pairs, 1 lone pair. Four domains, trigonal pyramidal, 107°.
  • CO₂ → 2 bonding domains (4 bonding pairs in total), 0 lone pairs on carbon. Linear, 180°.
  • SO₂ → 2 bonding domains, 1 lone pair on sulfur. Three domains, bent, about 119°.
  • BF₃ → 3 bonding pairs, 0 lone pairs. Trigonal planar, 120° — boron is happy with six electrons here.
  • H₃O⁺ → 3 bonding pairs, 1 lone pair. Note the positive charge removed one of water's lone pairs, so it's pyramidal like ammonia, not bent like water.
  • NH₄⁺ → 4 bonding pairs, 0 lone pairs. Nitrogen's lone pair became a bond to the extra proton, so the ion is a perfect tetrahedron at 109.5°.

Those last two are the clearest demonstration that lone pairs, not just atoms, decide shape: NH₃ and NH₄⁺ have the same central atom and the shape changes completely when the lone pair is used up.

What lone pairs actually do chemically

Shape isn't their only job. A lone pair is a pair of electrons available to be donated, which makes it the reactive heart of an enormous amount of chemistry:

  • It's what makes ammonia a base — the lone pair grabs an H⁺.
  • It's what makes water a hydrogen-bond acceptor, and therefore why water boils at 100 °C instead of −80 °C.
  • It's what makes a nucleophile nucleophilic — the lone pair attacks an electron-poor carbon.

So when you spot a lone pair, you've found both the reason the molecule is bent and the place it's most likely to react.

Common mistakes to avoid

  • Forgetting lone pairs when naming the shape. Water is bent, not linear, because two invisible lone pairs are in the way. You name the shape from the atoms you can see, but you count all the domains to find it.
  • Counting a double bond as two domains. Two bonding pairs, yes — but one domain. CO₂ has four bonding pairs on carbon and is still linear.
  • Treating outer-atom lone pairs as if they set the shape. Only the lone pairs on the central atom bend the molecule. The two lone pairs on each oxygen in CO₂ change nothing about its linearity.

FAQ

What is the difference between a lone pair and a bonding pair?
A bonding pair is shared between two atoms and holds them together; a lone pair belongs to one atom and is not shared. Because only one nucleus holds it, a lone pair spreads out more and repels neighbouring pairs more strongly.

Why do lone pairs repel more than bonding pairs?
A bonding pair is pulled tight into the narrow space between two nuclei. A lone pair is attracted by only one nucleus, so it stays closer to that atom and occupies a wider angle around it — pushing bonding pairs away and closing bond angles.

Do lone pairs count in VSEPR?
Yes. Lone pairs count as electron domains and determine the electron geometry, even though they don't appear in the molecular shape you name.

How do I know how many lone pairs an atom has?
Draw the Lewis structure and count the leftover electrons. As a quick check for neutral atoms: carbon usually has 0, nitrogen 1, oxygen 2, and a halogen 3.

The takeaway

Bonding pairs are shared and pinned between two nuclei; lone pairs belong to one atom and take up more room. Both count when you're working out shape, but only the bonding pairs show up in the name — which is exactly why water is bent and ammonia is pyramidal.

Start here → What Is a Lewis Structure? Dots, Bonds, and Octets and What Is a Valence Electron? Shells and Bonding. Next → [What Is VSEPR Theory?] (sibling), which turns this count into an actual shape, and [Electron vs Molecular Geometry] (sibling).

⏰ 5 Minutes in Chemistry — the study series from Chemistery

You just learned one topic the five-minute way. The series does it for your entire course — one printable page per topic: understand it, memorize it, test yourself. Five minutes. Next topic.

  • Vol 1 · Semester 1 — atoms, moles, stoichiometry, bonding & gases (22 sheets)
  • Vol 2 · Semester 2 — kinetics, equilibrium, acids & bases, electrochem (19 sheets)
  • Vol 3 · The Hard Stuff — cram charts & decision trees for the units worth the most points (15 sheets)

Built for advanced-level high school and first-year college chem. 56 sheets, printable, Letter + A4.

$19.99 $9.99 for all three — Use code BACK2SCHOOL — back-to-school price ends Sep 15.

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