The big idea: A water molecule has one slightly negative end and two slightly positive ends.
We call a molecule like this polar.
Nearly all of water's special properties — why it sticks together, dissolves substances and stores heat — come from this one fact.
A water molecule: oxygen (δ−) bonded to two hydrogens (δ+) in a bent shape.
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What the symbols mean: δ− (delta-minus) = a slight negative charge.
δ+ (delta-plus) = a slight positive charge.
These are partial charges — much smaller than the full charge on an ion.
Oxygen and each hydrogen are joined by a covalent bond — they share a pair of electrons.
But the sharing is not equal. Oxygen is more electronegative, which means it pulls the shared electrons closer to itself.
- Covalent bond
- A bond where two atoms share a pair of electrons.
- Electronegativity
- How strongly an atom pulls shared electrons toward itself.
- Polar covalent bond
- A covalent bond where the electrons are shared unequally, giving each atom a partial charge.
- Polar molecule
- A molecule with an uneven spread of charge — a positive end and a negative end.
The bent shape is the key: Because oxygen hogs the electrons, the oxygen becomes δ− and the two hydrogens become δ+.
The molecule is bent (the H–O–H angle is about 104.5°), so the two positive ends sit on the same side. The charges do not cancel out — so the whole molecule is polar.
One oxygen + two hydrogens, joined by polar covalent bonds.
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How this is tested: On Paper 1A (multiple choice) you are often asked to identify the bonding inside a water molecule (covalent) or which atom carries the δ− charge (oxygen).
On Paper 2 a 2-mark Draw question can ask you to draw and label a single water molecule.
IB-style question — draw and annotate a water molecule
Draw a labelled diagram of a single water molecule. Show the bonds between the atoms and the partial charges. [2]
How to score both marks
- Draw the three atoms. One oxygen (O) in the middle joined to two hydrogens (H), with the molecule shown bent (not in a straight line).
- Label the bonds. Each O–H line is a (polar) covalent bond — a shared pair of electrons.
- Add the partial charges. Mark δ− on the oxygen and δ+ on each hydrogen. (Mark 1: correct atoms and bent shape. Mark 2: correct partial charges.)
Final answer
A bent H–O–H molecule with δ− on O, δ+ on each H, and the O–H bonds labelled as polar covalent bonds.
✓ The diagram you should draw: Check yours has all four features: the bent shape, O bonded to two H, δ− on the oxygen and δ+ on each hydrogen.
A water molecule: oxygen (δ−) bonded to two hydrogens (δ+) in a bent shape.
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