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Flip to reveal answersDefine a hydrogen bond (in water).
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All 12 Flashcards — Hydrogen bonding between water molecules
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Question
Define a hydrogen bond (in water).
Answer
A **weak attraction** between a **δ+ hydrogen** of one water molecule and a **δ− oxygen** of another molecule.
Question
Does a hydrogen bond act within or between water molecules?
Answer
**Between** separate water molecules (a covalent bond acts **within** one molecule).
Question
Which two parts attract to form a hydrogen bond?
Answer
A **δ+ hydrogen** of one molecule and a **δ− oxygen** of a neighbouring molecule.
Question
Why can water molecules form hydrogen bonds at all?
Answer
Because each molecule is **polar** — it has a δ− oxygen and δ+ hydrogens.
Question
Is a hydrogen bond weak or strong compared with a covalent bond?
Answer
**Weak** — much weaker than a covalent bond.
Question
If each hydrogen bond is weak, why do they matter?
Answer
Because there are a **huge number** of them, so a **lot of energy** is needed to separate the water molecules.
Question
Define a covalent bond.
Answer
A **strong** bond **within** a molecule, where atoms **share a pair of electrons** (the O–H bonds in water).
Question
How is a hydrogen bond drawn in a diagram?
Answer
As a **dashed line** from a δ+ hydrogen of one molecule to the δ− oxygen of another, labelled **'hydrogen bond'**.
Question
Why is water liquid at room temperature when methane is a gas?
Answer
Water forms **many hydrogen bonds** that hold its molecules together; methane is **non-polar** and forms none.
Question
Name two of water's properties that come from hydrogen bonding.
Answer
High **boiling point**, **cohesion** (and a high **heat capacity**) — any two.
Question
Can one water molecule hydrogen-bond to more than one neighbour?
Answer
Yes — each molecule can hydrogen-bond to **several** neighbours at once.
Question
What does δ (delta) mean on an atom?
Answer
A **partial** (slight) charge — much smaller than a full ionic charge.
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