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A1.1.2—Hydrogen bonds in water

Water molecules are polar, so partial charges attract between neighbouring molecules to form hydrogen bonds that explain water’s distinctive physical properties.

Syllabus
First assessment 2025
Objective
A1.1.2
Level
HL

Exam analysis

Chance of appearing8%of analysed past papers
Latest appearanceMay 2025
Most common paper—
Typical marks1–3

Common command terms

  • Identify
  • Describe
  • Explain
  • Outline
  • Draw

Scoring notes

Common mistake
Drawing a hydrogen bond between atoms within the same water molecule.

Recent exam appearances

May 2025Paper1A HL · TZ11[ 1 ]A1.1.2—Hydrogen bonds in water
May 2024Paper2 HL · TZ16(a)[ 3 ]A1.1.2—Hydrogen bonds in water
May 2023Paper2 HL · TZ25(a)[ 2 ]A1.1.2—Hydrogen bonds in water
May 2023Paper2 HL · TZ14(b)(i)[ 2 ]A1.1.2—Hydrogen bonds in water
May 2023Paper2 HL · TZ14(a)(ii)[ 1 ]A1.1.2—Hydrogen bonds in water
Practice this objective

Coverage 2013–2025 · Updated 14 Jul 2026

Polarity Leads to Hydrogen Bonds Between Water Molecules

Each O-H bond in water is polar covalent because oxygen attracts the shared electrons more strongly than hydrogen. Oxygen is partially negative (delta-) and each hydrogen is partially positive (delta+).

Because a water molecule is V-shaped, its bond dipoles do not cancel. The delta+ hydrogen of one molecule is attracted to the delta- oxygen of another, forming an intermolecular hydrogen bond.

To represent two water molecules: draw solid O-H covalent bonds within each V-shaped molecule, label O as delta- and H as delta+, then draw a dotted line from H(delta+) on one molecule to O(delta-) on the other and label it hydrogen bond.

Many individually weak hydrogen bonds act together. This collective attraction helps explain cohesion and the relatively high energy needed to separate water molecules.

Do not draw a hydrogen bond between O and H within the same water molecule: that connection is a polar covalent bond.

Hydrogen bonds in water

Assessment in practice

1–2 marks
How it is assessed

This objective is assessed through structured response, multiple choice, commonly using Identify / Describe / Explain.

Command terms

Identify / Describe / Explain / Outline / Draw

What earns marks

Build the answer around this relationship: Unequal electron sharing makes each O–H bond polar.

Watch for

Drawing a hydrogen bond between atoms within the same water molecule.

Representative question

Question 1

[Maximum number: 3]

Outline how hydrogen bonds form in water.

Turn a water molecule until attraction appears

Water summary

  • Water is life's medium because substances can dissolve, move and react in it.
  • Unequal electron sharing and bent geometry make water polar; hydrogen bonds form between molecules.
  • Many hydrogen bonds produce cohesion, maintaining xylem columns and creating surface tension.
  • Adhesion is water-to-surface attraction and contributes to movement through narrow soil spaces and cellulose walls.
  • Polarity lets water hydrate ions and interact with polar solutes; dissolved particles can be transported and react, while non-polar substances are hydrophobic.
  • Compared with air, water provides more buoyancy and drag, transfers heat faster and changes temperature more slowly. Aquatic adaptations respond to these consequences.

Concept essentials

  • Unequal electron sharing makes each O–H bond polar.
  • Oxygen is partially negative and hydrogen is partially positive.
  • Hydrogen bonds form between different water molecules.
  • Disrupting hydrogen bonds requires energy.
  • Hydrogen bonding explains important thermal properties of water.